Solid State Ionics

The following sections are included:

• PREFACE

• SPONSORS AND SUPPORTERS

• CONTENTS

The technology of ionics is based on the generation and application of electrical fields at interfaces between mixed ionic and electronic conductors. Ions and electrons equilibrate both at these “ionic junctions”. In contrast to semiconductor junctions, the space charge region is more than three orders of magnitude narrower and has the dimension of a few atomic layer. Several contradictions have to be overcome in order to develop successfully practical devices. Most conflicts are related to chemical stability, fast kinetics, nonstoichiometries and electronic properties. Selection criteria for suitable materials will be presented and the possibilities of materials combinations to form junctions are being discussed.

The conventional Nernst-Einstein equation inherently presupposes that the charge carriers of different types migrate independently of each other. It is, thus, readily expected that the equation is to fail if the charge carriers interfere with each other upon their transfer. We have recently found that in mixed ionic electronic conductor compounds, mobile ions are interfering with electrons upon their migration and that that electron/ion interference leads to the breakdown of the conventional Nernst-Einstein equation. We will present the experimental evidences for the breakdown of the conventional equation.

If we would observe the persistent hole due to locally structural change, we can determine the potential energy for a locally structural change using a technique of the measurement of the thermal decay profile of hole, which is obtain from the so-called temperature cycling experiment. This energy will correspond to the potential barrier for the ionic motion through the conduction path in superionic conductors.

In this paper, usefulness of hole burning for study on ion dynamics in superionic conductors is discussed; one is about β″-alumina and the other about perovskite-type proton conductors. In β″-alumina, there are two different potential barriers through ionic conduction path. One of the potential barriers is higher than the activation energy for ionic conduction. It is considered from this result that an ionic interaction between the conduction ions will be important role for ionic migration in β″-alumina. In perovskite-type proton conductors, rotational motion of proton around oxygen ion was observed. Using these results, we can discuss an elementary migration of ions, and then ion dynamics in superionic conductors.

We prepared RSn₂F₅ (R=K and Rb) and examined the relation between structure and electric conductivity and the conduction mechanism by observing DTA, NMR, powder X-ray diffraction, and electric conductivity. The conductivity around 400 K was 10⁻³ S/cm for the K salt and 10⁻¹ S/cm for the Rb salt. The half width of ¹⁹F NMR is 40-50 kHz for all salts at a low temperature and 0.2 kHz around 400 K. The line width of ¹¹⁹Sn NMR decreased with increasing temperature and a sharp line was observed above 450 K. The spin-lattice relaxation times of ¹¹⁹Sn NMR showed a minimum near 400 K and the activation energy obtained was 41.0 kJ/mol for the K salt and 36.7 kJ/mol for the Rb salt. These findings indicate that the chemical shift and dipole interactions are averaged at the high temperature and the environment around Sn atom becomes octahedral since the F⁻ diffusion is increased. Therefore, ¹¹⁹Sn NMR spectrum shows a sharp line without anisotropic chemical shift.

Although Neutron Radiography (NR) is not so familiar to Solid State Ionics, it is possible to visualize the movement of ionic species using the NR technique, particularly in lithium ion or proton conductors, because the interaction of ⁶Li and ¹H with neutron is much larger than the other common elements and their isotopes (⁷Li and ²D). In this paper, the principle and the feature of this NR method will be mentioned. Furthermore, it will be demonstrated using our actual experimental results that the NR technique is useful in the field of Solid State Ionics to clarify the lithium distribution and lithium ion movement.

The interatomic distance dependence of the highest bonding orbital energy in AgI, CuI and CuBr are calculated. From such dependence, the superionic transition temperature is estimated by making connection with a theory of melting. The result of the calculation indicates that the above materials transform to the superionic phase when the energy variation reaches ≅0.1 eV.

The Li-ion conductivity is a sensitive function of the composition and the microstructure for the perovskite-type Li-ion conductor. In this study, the effect of sintering temperature and thus microstructure and Li loss on the electrical conductivity of Li-conducting La_0.57Li_xTiO₃ (x=0.3 and 0.35) were studied. The grain and the grain boundary conductivity were obtained from the impedance patterns.

As the sintering temperature increased from 1100°C to 1350°C, the Li content decreased due to the evaporation of Li during sintering. The samples were nearly fully dense after sintering at 1200°C or above While the grain conductivity increased with increasing lattice parameter, the grain boundary conductivity increased rapidly with sintering temperature due to the increasing grain size. The grain conductivity with sintering temperature was influenced by both the charge carrier concentration and the structural change due to Li evaporation. On the other hand, the grain boundary conductivity change was mostly explained by the microstructural change.

Refined natural kaolinite has been used as a starting material for preparing new lithium fast ion conductors Li_1+2x+yAl_xY_yTi_2-x-ySi_xP_3-XO₁₂ system by high temperature (∼1100°C) solid phase reaction for about 20h. The syntheses temperatures lower with increasing the value of x and y for the above system. X-ray powder diffraction showed that a Lisicon phase with space group exists in the composition range of x=0.1, y ⩽ 0.8; x = 0.2, y⩽0.6 and x = 0.3, y ⩽ 0.5, a second phase always exists in the above composition range. The composition with x = 0.2, y = 0.2 possesses maximum ionic conductivity of 7.64 × 10⁻⁵S/cm at room temperature, while at 673K the composition with x = 0.1, y = 0.4 possesses the best ionic conductivity of 8.21 × 10⁻³S/cm.

New lithium fast ion conductors Li_1+2x+yAl_xZn_yTi_2-x-ySi_xP_3-XO₁₂ system based on LiTi₂(PO₄)₃were prepared by high temperature (900∼1150°C) solid phase reaction for about 20h using refined natural kaolinite as a starting material. The syntheses temperatures lower with increasing the value of x and y for the above system. XRD analysis indicates that a Lisicon phase with space group can be found in the composition range of x = 0.1, y⩽0.7 and y = 0.3, x⩽0.3, while only when x=0.1, y⩽0.2 can a single Lisicon phase exist. A.C. impedance measurements show that the sample TZP has the best ionic conductivity of 1.61×10⁻⁴S/cm at room temperature and 4.83 × 10⁻²S/cm at 673K, its activation energy is 49.4KJ/mol in the temperature range of 473-673K.

Lithium fast ion conductors of Li_14-xZn_1-xYb_x(GeO₄)₄ system (hereafter referred to as LZYG)based on Li₁₄Zn(Ge0₄)₄ were prepared by solid state reaction at high temperature(~1100°C). A.C impedance measurements indicate that the best ionic conductivity is the initial composition with x=0.4 which reach up to 1.09×10⁻²S.cm⁻¹ at 400°C and its activation energy is 62.5kJ.mol⁻¹ in the temperature range of 200~400°C for the LZYG system. X-ray powder patterns showed that the LZYG system is a solid solution. The reaction of the hydrolysis of LZYG indicate the hydrolyzation gently increase with increasing the value of x.

Dawsonite type compounds NaAl(OH)₂CO₃and NH₄Al(OH)₂CO₃ have been synthesized by hydrothermal process and were chosen as the precursor for beta-alumina powder. The influences of acidity, temperature and composition of reaction systems on the phase component and particle morphology of products were investigated systematically. Experimental results showed that nanosized NaAl(OH)₂CO₃ and NH₄Al(OH)₂CO₃ hydrothermally coprecipitated from aqueous solutions under appropriate conditions instead of forming solid solutions.

A Superionic system Agl-Pbl₂-Ag₂O-B₂O₃ with two compositions have been prepared. The pellatised form of the samples have been subjected to Conductivity, Modulus and Dielectric analysis for various temperatures and frequencies. The activation energy calculated for the present samples are found to be varying between 0.09 to 0.10 eV. The effect of polarization at the electrode has been observed from conductivity spectra. From the impedance and modulus analysis, it has been found that the system is non-ideal and there exists distribution of relaxation times which is independent of temperature.

A Superionic system Agl-MCl₂-Ag₂O-V₂O₅ where (M=Cu, Zn, Ca & Hg) have been prepared. The pellatised form of the samples have been subjected to Conductivity, Dielectric analysis for various temperatures The activation energy calculated for the present samples are found to be varying between 0.10 to 0.19 eV. The effect of substitution of metal chlorides on conductivity and dielectric constant are studied.

AgI nanoparticles were prepared in large-scales by quenching the AgI melt in liquid nitrogen. XRD patterns showed that all of the nanocrystals were almost Y-AgI, and the size of the nanocrystals was about 9~15nm. UV-vis spectrum indicated that the band gap of the nanoparticle was 0.11eV less than that of bulk AgI. Alternating complex impedance analysis showed that the conductivity at room temperature of nanoparticles was 4.2×10⁻⁵Ω⁻¹cm⁻¹, and the responding conductivity activation energy was less than that of bulk AgI(0.25eV compared to 0.60eV). Furthermore, an anomalistic phenomenon was observed that the phase transition of common phase to superionic phase of AgI nanocrystals was a gradual process between 140°C and 235°C instead of a break at 146°C for bulk AgI.

Analysis of experimental data obtained for nanocomposites AgI-Al₂O₃, RbNO₃-Al₂O₃ and CsHSO₄-SiO₂ shows that unusual physical properties of ionic salts in the nanocomposite are caused by the presence of amorphous interface phases. Thermodynamic reasons of the formation of nanocomposite are considered and the criterion of spontaneous spreading the ionic salt along the oxide surface is proposed. Possible reasons of the stabilisation of the amorphous phase in composite are discussed. Concentration and thickness of the interface layer are estimated.

There is an intimate connection between crystal structure induced disorder, phonons and physical properties such heat capacity and thermal expansion that bear on the ion conducting properties of superionic conductors such as AgI. We consider in this paper the genesis of these contributing factors with particular reference to silver iodide. Attempts are made to account for the unusual experimental results observed in silver iodide.

Bulk AgI is a well known superionic conductor. A new method—electrochemical dual liquor deposition (EDLD) has been developed to produce AgI nano-wires. The AgI was formed within the nano-channels of Al₂O₃ template through electrochemical wet processing. Due to regularity of the template, the nano-wires of AgI were formed uniformly and parallel each other. Since AgI nano-wires were formed within the nano-sized channels of Al₂O₃ template, the diffusion of Ag+ ions can only occur in one dimension. The aspect ratio of the nano-wires ranged from 30 to 100.

The diffusion phenomena of thallous ions (Tl⁺ ions) through solid-liquid interface of liquid Tl⁺ ions diffusion source and sodium chloride (NaCl) or potassium chloride (KCl) single crystals are studied by optical method. The characteristic absorption peaks of Tl⁺ center in NaCl or KCl single crystals were used as the tracer for measurements.

NaCl or KCl single crystals and the powder of TlCl are placed in a crucible together and heated at a given temperature above the melting point (430°C) of TlCl. The optical density of the Tl⁺ center was measured at various distances from the diffusion surface.

The temperature dependence of diffusion constant could be evaluated.

The diffusion constants are evaluated at various temperatures.

The results show that the diffusion constant of solid-liquid interface is about 10³ times larger than that of solid-solid interface of KCl and TlCl, in KCl (Tl).

The superionic conductivity and dielectric response of heavily doped fluorite-structured Ba_1-xR_xF_2+x (R = La, Pr, Nd, Gd, Tb, Y, Sc; x = 0.005 – 0.45) crystals are reported. The highest ionic conductivity is found for R = Sc, x = 0.1. Upon ScF₃ doping, small Sc³⁺ ions rearrange their surroundings, create excessive fluoride interstitials and bring about a high ionic conductivity. For all dopants, the concentration dependence of the ionic conductivity is non-linear. A monotonous dependence is found for La³⁺ doping only. Upon doping with Nd³⁺, Gd³⁺,Tb³⁺, Y³⁺ and Sc³⁺ ions, a maximum of the conductivity is observed at x = 0.1 - 0.2. Upon Pr³⁺ doping, this maximum is splitted. The influence of defect clustering on the concentration dependence of the conductivity is discussed.

The ionic conductivities of orthorhombic rare earth trifluorides, and of tysonite-structured ones are investigated The temperature dependences of the conductivities of various orthorhombic rare earth trifluorides are close one to another The conductivities are significantly lower than those of tysonite-structured crystals. The highest conductivity is found for LaF₃: 5 m/o SrF₂ solid solutions (σ₅₀₀ = 2.4.10⁻² S/cm, ΔH = 0.35(1) eV). In all rare earth trifluorides, the ionic conductivity is almost isotropic. The anisotropy of the permittivity is significant In both structures, the most probable fast conduction paths are calculated and compared. The cause of large difference of the conductivities of both structures is discussed.

A series of RSbF₄ were synthesized and investigated their dynamic structures using DTA, impedance measurement, XRD and NMR. Only K salt transformed into a fluorite structure at 455 K. The conductivity reached to 10⁻²Scm⁻¹ at 500 K. This high temperature modification was stable in the cooling process and the mechanism of the anionic diffusion was examined by ¹⁹F NMR.

Oxygen nonstoichiometry (δ) YBa₂Cu₂CoO_6+δ was determined by double iodometric titration technique. It is found that the value of δ is strongly affected by the temperature and oxygen partial pressure. An appreaciable oxygen permeation flux through a 1.2 mm thick dense sample were observed at elevated temperatures under a relatively small oxygen partial pressure gradient (Po₂(h)=0.209 and Po₂(l)=10⁻³ atm). The oxygen permeation is a thermally activated process, the apperant activation energy being 64.5±0.4kJ/mol. From the measured oxygen nonstoichiometry and permeation flux, the oxygen chemical diffusion coefficient is derived.

A natisite-type single crystals Li₂TiGeO₅ and Na₂TiGeO₅ were grown by flux crystallization and pulling (Czochralski) methods respectively. These materials possess layered structure and electrical conductivity of the crystals has been studied over a wide temperature range along different crystallographic axes. Giant anisotropy of conductivity was observed: σ(II a-axis)/σ (II c-axis) are 10²-10³ for sodium-containing crystals and 10³-10⁴ for lithium-containing crystals.

This paper reviews recent nuclear magnetic resonance (NMR) studies we performed in the superionic glass xLiF·(1 − x)LiPO₃ in an attempt to better understand various microscopic aspects of this compound. Magic–angle spinning, spin-echo double resonance (SEDOR), and spin-lattice relaxation experiments are presented which yield structural and dynamic information.

The thermal, electrical, and electrochemical properties of the Li₂S-SiS₂-Li_xMO_y(Li_xMO_y: lithium ortho-oxosalt, M=Si, P, Ge, B, Al, Ga and In) oxysulfide glasses were reviewed. The Li₂S-SiS₂ sulfide glasses with small amounts of Li_xMO_y exhibited high glass stability against crystallization and high conductivity of about 10⁻³ S cm⁻¹ at room temperature. The glass with 5 mol% of Li₄SiO₄ showed a wide electrochemical window and high thermal stability in contact with Li metal. The glass structure of the oxysulfide glasses was analyzed by using solid-state NMR and X-ray photoelectron spectroscopy. The glasses with small amounts of Li_xMO_y consisted of the SiS₄ tetrahedral units and SiO_nS_4-n (n=1,2,3) units in which the silicon atoms were mainly coordinated with both bridging oxygen and nonbridging sulfur. The presence of the SiO_nS_4-n units brought about high conductivities and high thermal stability in these glasses. The solid-state battery with the oxysulfide glass with 5 mol% Li₄SiO₄ as solid electrolytes worked as a lithium secondary battery and exhibited excellent cycling performance.

Ionic conductivity and electrical relaxations in fast ion conducting glasses (also known as ‘ion dynamics’) is usually investigated from electrical conductivity relaxations, represented by the ac conductivity from near zero frequency (dc) to the far or mid infrared spectrum, to which relaxations of the ion and network motions contribute. In the present work ion dynamics of LiF-KF-Al(PO₃)₃ glasses is reported. Glasses in this system have been synthesised via conventional melt-quench route. The glass-transition temperature (T_g), dc conductivity and electrical relaxations were studied. The conductivity spectrum of the 0.8 LiF-0.2Al(PO₃)₃ glass was recorded at room temperature covering 17 decades in frequency. A binary composition was investigated over a broad band of frequency from 1mHz to 150 THz employing various techniques. A complete conductivity spectrum was constructed by combining the impedance measurements at low frequencies and the dielectric data obtained at high frequencies. A maximum conductivity of 38 (Ω⁻¹ cm⁻¹) at 3.4 × 10¹³ Hz agreed with the theoretically predicted value. For mixed cation glasses, the frequency dependent conductivity was measured in the frequency range 20 Hz to 2 GHz and at temperatures 100 K ≤ T ≤ 523 K. While the dc conductivity showed a characteristic minimum with composition, the ac conductivity also exhibited the mixed alkali effect. This is the first experimental observation and will be discussed.

The relationship between average electronegativity and some properties of superionic glasses has been studied. It is shown that the ionic conductivity and the network expansion by salt doping obey a striking scaling relation when arranged against the average electronegativity. The sound velocity data indicated that the glass become rigid at a particular value of the average electronegativity. All of these data indicate the usefulness of the average electronegativity in studying the behaviour of complex chemical species such as superionic glasses.

We present a novel power law results for the disordered systems using newly discovered non-Debye relaxation response function. The non-Debye relaxation function is found to be (Φ* (t) = exp[−t/τ*], where τ* = τ' - iτ" = τ^g/i^(1-g) = 1/ω*, and g is an exponent. The effect of spatially randomly varying free energy barriers is appeared through the phase factor g and it is responsible for the stretching of Debye relaxation time τ to τ^g in Φ*(t). At the impedance loss peak frequency ω_p = 1/τ^g the impedance loss tan[δ_p], which signifies the energy dissipation, attains a minimum and it is related to the g(δ_p). Many experimentally known features of the power law are explained satisfactorily. Present model is compared with the experimental data and results show an excellent agreement.

The conductivity of glassy material Li₂O:4MnO_2-x:4B₂O₃, prepared by quenching the melt in air has been studied by impedance spectroscopy and X-ray diffraction. Two kinds of conductivity anomalies have been observed around the crystallization temperature. One conductivity anomaly is observed for the pristine glass specimen annealed at 400°C in air, the conductivity increases quickly at first and then declines slowly. While the conductivity for specimen annealed in argon decreases slightly with annealing time. Moreover, the conductivity of specimen annealed in air is one order of magnitude higher than that of specimen annealed in argon. This phenomenon is due to the effect of the oxygen partial pressure on the concentration of small polaron. The other conductivity anomaly is observed for the annealed specimens heat-treated at 420°C. It was found that the conduction process is rather complicated for the glassy LiMnBO annealed for 150 minute. Below 200°C, the conductivity obeys Arrhenius relation. Above 350°C, the crystallization of MnBO₃ makes the decrease of conductivity by one order of magnitude. In between the conductivity is enhanced by the redistribution of free volume.

Metal cation doping into the sodium borate glass was carried out using the solid oxide electrochemical doping (SOED) method which has been developed in this laboratory. The electrolysis cell consists of an Anode (Ag, K₂CO₃, Li₂CO₅) | glass | Na-β″-Al₂O₃ | Cathode (Ag) where cation was doped into the glass under electrical force. On the other hand, Na⁺ in the glass migrates into the Na-β″-Al₂O₃ for maintenance of the electrical neutrality in the glass. Various monovalent cations such as Ag⁺, K⁺, and Li⁺ are easily substituted for Na⁺ in the glass using this method. This doping mechanism is briefly discussed.

Rechargeable lithium ion batteries (LIB) are now recognized as one of the important and viable power sources for portable applications. Rapid progress is expected in the coming years by way of improved technology, scale-up and find new and novel uses for LIB. The recent trends in the research on the battery materials is presented. Work done by our group on the technology and materials aspects of LIB are briefly described.

To improve the cycle performance of LiMn₂O₄ cathodes, Co and Ni were substituted for Mn. The Li(Mn₁-_δM_δ)₂O₄ (M=Co, Ni, δ=0, 0.05, 0.1, 0.2) cathode materials were synthesized by using typical solid state reaction. Their crystal structures and microstructures were analyzed and their electrical properties were systematically evaluated as follows; charging-discharging capacities and cycle performances by the cut-off voltage changes and stable potentials by an electrical voltage spectroscopy. The (LiMn_0.9Co_0.1)₂O₄ material was the best cathode for properties above. Its optimum cut-off voltages are 3.5 V to 4.5 V and initial charging and discharging capacities are 119 mAh/g and 113 mAh/g, respectively.

A simplified technique was introduced to synthesize LiMn₂O₄ directly from lithium acetate and manganese acetate. The reaction process was investigated by IR spectroscopy and TGA. The resulted materials show a good cycling performance.

The substituted spinel LiM_yMn_2-yO_4-zF_z (M = Al/Cr) have been prepared to compensate for the initial capacity reduction in LiM_yMn_2-yO₄ and improve the cycle performance of . The shape of the voltammetric peaks in the 2-5V region and impedance spectra polarized at the high potential for LiCr_y/2Al_y/2Mn_2-yO_4-zF_z suggests that changes in the structure affects the kinetics of the electrode of LiM_yMn_2-yO_4-zF_z less than that of the parent LiMn₂O₄. The increase of the diffusion coefficient of lithium ion calculated from the PITT could be explained by considering that the binding energy of Mn-O is smaller than that of M-F.

Three lithium-rich spinel Li_1+xMn₂O₄ oxides were synthesized from industrial grade precursors. Galvanostatic charge/discharge tests at 55°C and cyclic voltammetry experiments were conducted to evaluate the effect of the extra lithium content on the electrochemical performance of the oxides. Sample Mn-C with the largest Li/Mn ratio exhibited best cycling performance at elevated temperature, owing to: (1) suppression of manganese dissolution and Jahn-Teller effect due to the increased average valence of manganese, (2) structural stability due to homogeneous reaction during intercalation/deintercalation, and (3) increased resistance against overcharge, and reduced volume change during cycling as a result of the presence of residual lithium in fully charged state.

Layered Li-Mn based material, Li_2/3(Ni_1/3Mn_2/3)O₂, with O2 structure has been prepared by ion exchanging the corresponding P2 structure sodium bronze, Na_2/3(Ni_1/3Mn_2/3)O₂. X-ray diffraction studies show that the compound can be indexed in the hexagonal structure with a= 2.86 Å, c= 9.99Å. Electrochemical testing of the material as cathode with lithium metal anode shows an initial discharge capacity of 187 mAh/g, divided into two plateaus centered near 2.8 and 3.8 V. At C/20 rate the discharge capacity stabilizes at 149 mAh/g at the end of 30 cycles after an initial drop during the first few cycles. The cycling performance and the nature of the cyclic voltammograms reveal that the material does not convert to spinel structure.

Chromium doped spinel LiMn₂O₄ were prepared by solid-state reaction and metal-complex method, respectively. XRD patterns indicate that these compounds are pure spinel phase. SEM images shows that different synthesize methods can get particles in different shapes. The doped spinel made by solid-state reaction shows higher charge-discharge efficiency in the first cycle, but its capacity fades faster than the one made by metal-complex method. Li_0.94Cr_0.11Mn_1.90O_4+δ made by metal-complex method has lower efficiency in the first several cycles, but can remain as much as 85% of the reversible capacity after 400 cycles. FTIR spectra show that there are passivating films formed on the surface of the cathode that is similar to the case of those on oxide anode. In the case of Li_0.94Cr_0.11Mn_1.90O_4+δ with larger specific surface area, the charge contributed to the passive layer formation can be much higher. By comparing the cycling performance of these spinel type compounds, it can be conclude: i) Cyclicity of spinel LiMn₂O₄, can be improved by cation doping; ii) The passivating films on cathodes plays an important role in the electrochemical performance.

Adding impurity ions to the body phase of spinel LiMn₂O₄ is a useful measurement to improve its electrochemical performances. Surface treatment is also a possible solution for mending the cathode materials. In this study, an electrochemical method was used to modify the spinel LiMn₂O₄. Here potassium fluoride aqueous solution was used as the electrolyte, LiMn₂O₄ film and nickel film were served as the working electrode and counter electrode, respectively. With a charge current of 100µA, the LiMn₂O₄ films were treated for several hours in the electrolyte system, then washed by distilled water to remove the residual electrolyte, followed by vacuum drying under 55°C. X-ray photoelectron spectroscopy (XPS) indicates that the fluorine anions had appear on the surface of LiMn₂O₄ after the electrochemical process. Scanning electron microscope (SEM) images show that the apparent morphology of these cathode material particles had been changed. Galvanostatic charge-discharge curves show the charge-discharge plateaus of the anion-modified spinel LiMn₂O₄ are different from those of untreated one. The influences of the modification on the properties of spinel are discussed in detail.

Spinel-type Li_xMn₂O₄ cathode materials were prepared by melt-impregnation method with different Mn sources and characterized by BET, XRD and TEM as well as electrochemical testing. The results demonstrated that the cathode material prepared with CMD as Mn sources has smaller particle size, higher first charge and discharge capacity, poor cyclic performance, whereas the cathode material prepared with EMD as Mn source has larger particle size, lower first charge and discharge capacity, better cyclic stability. These can be attributed to difference of Mn sources and specific surface areas and purities of Mn sources.

The spinel LiM_xMn_2-xO₄(M=Mg, Al, Ni, Cr, Zn, Cu; x=0.1, 0.2, 0.3, 0.5) were prepared using solid-state reaction .XRD spectroscopy and electrochemical methods were used to examine their structures and properties. All samples exhibit approximately 4 V red-ox potentials (vs. Li⁺/Li) as LiMn₂O₄, but the capacities were not identical. Among these, the less the amount of the doped metal M, the more their initial capacities in 4V region. Their initial capacities are discussed in detail and concluded.

In this work, we will report some results about comparison of electrochemical performance of doped LiM_xMn_2-xA_yO_4-y (which M = Al, A = F) which are synthesized by different synthetic methods. The structure of doped LiM_xMn_2-xA_yO_4-y spinel have been characterized by using XRD and Raman techniques. It is shown that doped LiAl_xMn_2-xF_yO_4-y has the best performance in the materials studied. The role of doping element and their effects on the performance of the compounds are also discussed.

The two doped LiMn₂O₄, LiM_0.006Mn₂O₄ (M=La, Nd) (the first system) and LiLa_xNd_0.006-yMn_1.994O₄ (x= 0.006, 0.004, 0.002, 0) (the second system) were perpared by microwave-polymer (m-p) process. XRD test showed the samples prapared by m-p process had fine crystallinity, and the electrochemitry measurements showd their capacity and cyclabality are improved. The chronoamperometic and EIS test indicated that doped LiMn₂O₄ with Nd³⁺ had bigger diffusion coefficien, LiMn₂O₄ doped with La had a better cyclabality. Then magnetic test was conducted to determine the Li⁺diffusion bahavior. It was found that La was favourable for the cyclablitiy, while Nd was better for the insertion of Li⁺. So LiMn₂O₄ doped with La mixed Nd in the second way was suitable for the Li ion cells.

In this paper, the various nano-structured materials such as spinel LiMn₂O₄ nanotubes/nanowires and carbon nanotubes have been prepared by using porous alumina template. The prepared template and materials have been characterized by AFM and TEM techniques. It is shown that size of the nanotubes can be conveniently controlled by using template method.

The spinel LiMn₂O₄ is a promise alternative of the layered LiCo0₂ as cathode for lithium-ion battery. Due to the poor electrochemical performance at elevated above 55°C temperature, its commercial application was so far limited. We have investigated the cycling capability at 55°C and after 55°C storage of the spinel, synthesized at different temperature, Li/Mn ratio and with Co-dopant. Although the results showed some improvement, the cycling capability was not yet in competition with that at room temperature.

The LiMn₂O₄ instability in the electrolyte containing LiPF₆ observed at elevated temperature had been suggested to result in the rapid capacity fading. It has been thus reported that surface modification could improve the electrochemical performance at elevated temperature. We expected that the spinel could be coated by the layered LiCoO₂, which possesses excellent performance for the Lithium-ion battery application. The solid state reaction of the spinel LiMn₂O₄ was then investigated and some preliminary result was reported in this paper.

In this work a new method has been developed to synthesize lithium nickel cobalt oxide (LiNi_0.8Co_0.2O₂) as cathode materials for rechargeable lithium batteries. It was clarified from these investigations that a sol-gel complex could be formed from basic cobalt carbonate, basic nickel carbonate, lithium carbonate by adding citrate as the complex agent. LiNi_0.8Co_0.2O₂ prepared using this sol-gel method shows a higher cycling capacity of ~190 mAh g⁻¹ and good rechargeability.

Layered LiCoO₂ was prepared with microwave- polymer network (m-p) process. XRD and SEM tests showed the samples prapared by m-p process had fine crystallinity, and the electrochemitry measurements showed its capacity and cyclic ability were improved. The chronoamperometic and cyclic voltammograms tests indicated Li⁺ diffused easily in LiCoO₂ prepared by m-p process.

Spherical β -Ni(OH)₂ was prepared from different nickel salt by homogeneous complexing precipitation method. Its charge/discharge and cyclic voltammetry properties were studied. We found that there are much differences in electrochemical properties of the prepared Ni(OH)₂. The raw materials and the materials during charge/discharge were studied by XRD and FTIR measurements. The reasons why there are differences were analysised theoretically.

Molybdenum and tungsten substituted layered oxides Li_n+xM⁺⁶_yV_3-yO₈ (M=Mo, W; n = f(y))} with Li_1-xV₃O₈ structure have been synthesized by solid state reaction between V₂O₅, Li₂CO₃ and MoO₃ (or WO₃). The upper limits of Mo and W concentration (y=0.25 and y=0.20 respectively) in Li_n+xM⁺⁶_yV_3-yO₈ solid solutions was determined by XRD analysis. It was found that polycrystalline solid solutions with molybdenum content close to the upper concentration limit (y≥0.2) have discharge capacity approximately equal to the theoretical value for this structure (x=3). The lithium superlattiee ordering process was observed in these solutions for Li composition range x=0.94-1.85.

Li_1+xV₃O₈ was synthesized at 400-450°C by a sol-gel method in which a citric acid solution was added to an aqueous solution of LiNO, and NH₄VO₃. The influences of synthesis conditions on its first discharge capacity was investigated by chermogravimetric analysis. The structure of Li_1+xV₃O₈ was characterized by infrared. X-ray diffraction, scanning electron microscopy. The relationship between the structure and the electrochemical performance were investigated. The resultant product synthesized under the optimum synthesis conditions showed a high discharge capacity of 350 mAh/g, which is promising an excellent cathode material for high-energy, long-life rechargeable lithium-ion batteries.

BaFeO₄ was synthesized by solution reaction between Ba²⁺ ion and FeO₄^2- ion. Li-doped BaFeO₄ was prepared by ball mill solid-state reaction between BaFeO₄ and LiOH. XRD spectroscopy and electrochemical methods were used to examine their structures and properties. The discharge capacity of barium ferrate was examined at room temperature. The cell was charged (Li released) to 4.5 V and discharged (Li inserted) to 0 V at a constant current of 0.1 mA per 0.01g BaFeO₄. The curve (Fig.2) shows that barium ferrate working in the high-potential range (3374 to 2618 mV versus Li/Li⁺) is not suitable for use as positive-electrode active material in Li-ion batteries because of its discharge capacity low down to 0.475 mAh/g, The curve (Fig.3) shows that barium ferrate working in the low-potential range (290 to 0 mV versus Li/Li⁺) is suitable for use as negative-electrode active material in Li-ion batteries because of its discharge capacity high up to 294 mAh/g.

The flatband potential V_tb of n-γ-MnO2 is determined through electrochemical impedance using [Fe(CN)₆]³⁻ as probe; the bulk carrier concentration calculated, about 10¹⁷/cm³. According to the flatband potential determined and other parameters, the bandedge of γ-MnO₂ is showed, and the rate constants of electron transfer is calculated at γ-MnO₂/[Fe(CN)₆]³⁻ interface.

Alloy-based anode materials used for Li ion batteries have attracted increasing interest due to their higher theoretic capacity. In this paper, our recent studies on nanosized alloy-based anode materials are summarized, including Si, Sb, SnSb and nano-SnSb deposited on carbonaceous particles. It has been found that the key factor for improving the performance of nanosized alloy-based anode materials is to prevent electrochemical agglomeration of nano-alloy. Among these materials, core/shell structured carbon/nano-alloy composite materials show larger specific gravity capacity and volume capacity, higher tolerance to large current density, better cyclic performance and controllable potential profile, due to their special microstructure and electrochemical properties.

Ultrafine SnSb_0.14 and SnO powders as hosts for lithium insertion show high irreversibility in the first cycle. This study involves a combination of the tin-containing hosts with Li_2.6Co_0.4N for new composite anodes in lithium-ion batteries. The mixed-host electrodes show a high efficiency in the first cycle and good cycle performance.

Nano-sized SnSb alloy was deposited on the surface of MCMB, needle coke and PCG respectively, by a co-precipitation method in alcohol solution. The composite materials can eliminate the aggregation of nano-alloy effectively and show better cyclic performance. Larger reversible capacity has also been achieved because both SnSb alloy and carbon are active materials. The voltage profile of the composite materials can be controlled by choosing different carbon and alloy materials.

A series of Ni-deposited natural graphite composite materials have been prepared using hydrothermal hydrogen reduction method. The Ni particles are mostly distributed on edge planes with the diameter around 300nm. The electrochemical performance of these composites as anode active material for lithium ion batteries has been studied. It was found that the samples with deposited nickel particles show higher discharge capacity under higher current density. The higher rate performance of Ni-deposited graphite samples is related to their lower electron transfer resistance and the improvement of electronic conductivity.

This paper is concerning to prepare modified natural graphite which is low-cost and advanced materials used as lithium ion battery anode using the way of cladding natural graphite with epoxy resin. The results shows that the specific capacity and circular performance of the modified natural graphite, which is prepared in the range of 600°C and 1000°C, have been apparently improved compare with the not-modified natural graphite. The first reversible capacity of the modified natural graphite is 338mAh/g and maintain more than 330mAh/g after 20 charge/discharge circles.

We modified graphite by covering the surface with polymer (e.g. furfruan resin) to form a carbonized film. The modification of graphite surface greatly improved the performance of carbon anode for lithium ion battery. SEM and XRD results proved that the modification of graphite surface benefit to reduce the particle size of graphite, provide more active sites of Li⁺ intercalation. Chronocoulometry showed that the modified graphite could improve the diffusion and transition rate of lithium ions. FTIR spectra showed that the modification of graphite surface could effectively prevent solvated lithium ions cointercalating.

The investigation of solid state interphase (SEI) layer on Ag and Au electrodes in Li batteries by surface enhanced Raman scattering (SERS) technique is reported. The results indicate that SERS may open a new way to study the SEI film in Li rechargeable batteries.

Modified natural rubber polymer hosts having low transition glass temperatures have been investigated for use in polymer electrolytes. Two types of modified natural rubber, namely 25% epoxidised natural rubber (ENR-25) and 50% epoxidised natural rubber (ENR-50) were employed in conjunction with poly(ethylene oxide), PEO. Results are reported for ionic conductivity and thermal properties for both unplasticized and plasticized polymer electrolyte systems with lithium triflate. The samples were in the form of free standing films with the thickness 0.2-0.5mm and mixtures of ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticizers. Unplasticized modified natural rubber based systems exhibit ionic conductivities in the range 10⁻⁶ to 10⁻⁵ S cm⁻¹ at ambient temperatures. Incorporating 50% of EC/PC by weight fraction of polymer (ENR/PEO) to the systems yielded mechanically stable films and ionic conductivities in the range of 10⁻⁴ S cm⁻¹ at ambient temperature.

Composite polymer electrolytes based on alumina fiber and (PEO)₈-LiClO₄ were prepared by solvent casting technique. SEM analysis indicated that fibers homogeneously distributed in PEO matrix and effectively prevent the formation of microcracks in the composite polymer electrolytes while they were quenched from higher temperatures. Complex impedance results demonstrated the effectiveness of the additives on the ionic conductivity of the composite polymer electrolytes. Total ionic conductivity as high as 6.5×10⁻⁴Scm⁻¹ at 80°C was obtained for the composited polymer electrolyte with 20wt% alumina fiber. Thermal creep performances of the PEO based polymer electrolytes were also improved remarkably, especially at higher temperatures.

In this work, the effect of addition of the inert filler α-Al₂O₃ on the conductivity enhancement of the plasticized, PEO based solid polymer electrolytes has been studied. By this method, conductivities of the order of 10⁻⁵ S cm⁻¹ at room temperature has been obtained by the addition of inert ceramic powder, α-(Al₂O₃) of grain size 0.3 μm, to a plasticized polymer electrolyte LiCF₃SO₃[0.5PEO+0.5EC]₉. These polymer electrolyte films were prepared by solvent casting method. Thermal properties of the electrolytes were evaluated from DSC measurements. Complex impedance spectroscopy, in the frequency range 5Hz - 13MHz and in the temperature range −20 °C to 100 °C was used to obtain the ionic conductivity and dielectric relaxations. A stable amorphous phase was formed after the addition of Al₂O₃ particles and the conductivity values of the composite plasticized electrolyte ranged from 10⁻⁵ to 10⁻³ S cm⁻¹ over the temperature range 27-110 °C. Conductivity isotherms of LiCF₃SO₃[0.5PEO+0.5EC]₉ + x wt.% Al₂O₃ system exhibit the maximum conductivity at x = 5 for all temperatures, and the highest conductivity of 2.6 × 10^-3 S cm^-1 was obtained for this sample at 108 °C. The conductivity vs. temperature behaviour was found to be of VTF type, for all the complexes studied.

Polymer films in epoxy resin-polyethylene glycal interpenetrating polymer networks containing iodine were prepared. The I⁻ anion conductivity has been measured using impedance method. The results show that at first the anion conductivity gradually increased with iodine contents, and then increased rapidly. The electronic conductivity in this system was observed. The electronic transition number ~ 9 %. Above results may be explained by I⁻ or poly iodine anion migration.

Electrical conductivity studies have been carried out on liquid and gel electrolytes of lithium perchlorate (LiClO₄) in propylene carbonate (PC), ethylene carbonate (EC), dimethylacetamide (DMA), dimethylformamide (DMF) and their binary and ternary mixtures. Gel electrolytes were prepared by the addition of polymethylmethacrylate (PMMA) to above liquid electrolytes in different weight ratios. The conductivity of electrolytes has been found to be of the order of mS/cm and it depends upon the solvent (single, binary, ternary) used and varies as σ(ternary) > σ(binary) > σ(single). Maximum room temperature conductivity of 1.2×10⁻² S/cm is observed for liquid electrolytes using PC+EC+DMF in equal volume ratio as the solvent at 1M salt concentration. The variation of conductivity of gel electrolytes with polymer content and temperature has been found to be very small and is similar to that observed for the corresponding liquid electrolytes which suggest the liquid like behaviour of these polymer gel electrolytes.

Microporous films composed of PVDF-HFP were prepared by the phase inverse process. Electric properties of these microporous film and Celgard^®2300 using as membrane for Li-ion batteries have been measured and compared. PVDF-HFP based membrane adsorbed electrolyte has ionic conductivity above 10⁻³ s/cm at 25 °C, while the Celgard^®2300 in the same case has ionic conductivity was 6.7*10⁻⁴s/cm at room temperature. It is stable up to in electrolyte and has good interfacial character and long term stafibilyty for lithium electrode.

The redox behaviour of poly-N-methylpyrrole (PNMP) conducting polymer films doped with CIO₄^- ions has been investigated using cyclic voltammetry and electrochemical quartz crystal microbalance (EQCM). The analysis of the shift of peak potentials with the concentration of the cycling electrolyte using Nernst equation showed that in PNMP films, polymerized and cycled in the presence of small anions, moving species are anions. The EQCM measurements on PNMP films confirmed the involvement of anions in the redox process and showed the water transport also takes place in a direction opposite to that of anions.

The samples of epoxy resin-PEO400 IPN containing NaSCN salts were prepared in electric field. The conductivity was measured by impedance method. Experiment results show that the conductivity increased with increasing electric field strength in the region of E=0 to E=20v/cm at a given temperature, and reached a maximum value, which is greater more than one order of magnitude than that of no field. After this peak, the conductivity decreased rapidly with the electric field strength above 20v/cm. The conductivity enhancement was explained by the molecular micro-structure orientation along the direction of electric field. This presented a favorable passageway for ion migration. The conductivity decrease may be due to micro-structure damage by stronger field.

The samples containing various grain sizes ZrO₂ were prepared from PESC and NaSCN. The complex impedance was measured. The conductivity calculated. Experiment results show that the conductivity enhancement has a strongly dependent on the DSPP sizes. For samples with smaller sizes(≤1 μm) of ZrO₂ the conductivity increased. For samples with ZrO₂>1 μm) the conductivity decreased. Furthermore, the smaller sizes is, the greater conductivity is. Conductivity is inverse proportional to radius of ZrO₂ particles. This conclusion may be common regulation for all DSPP effects.

Nafion membranes were respectively doped with alkali ions. The methanol permeability and conductivity of these membranes were investigated at room temperature. Correlation between the alkali ions and the methanol permeability as well as that between the alkali ions and conductivity was established. A substantial methanol permeability depression was recorded following the ions series H⁺>Li⁺>Na⁺>K⁺>Cs⁺. The conductivity of alkali ion-doped nation membranes was also reduced to some degrees. The discussion of these results is based on changes produced by alkali ions in the membrane microstructure. It is found that Cs-doped Nafion membranes are most impermeable to methanol, whose conductivity, however, is reduced by over one order of magnitude. It may be ideal in relation to application in DMFCs technology to enhance the energy efficiency of DMFCs significantly.

Polymer gel electrolytes based on polymethylmethacrylate (PMMA) and lithium triflate (LiCF₃SO₃) with dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC) and their mixtures as solvents have been studied. The ionic conductivity results for the gel electrolytes are compared with those of the corresponding liquid electrolytes and are found to be very similar. Gels prepared by using ethylene carbonate as one of the solvent have been found to crystallise at low temperature. However the replacement of EC by propylene carbonate (PC) and γ-butyrolactone (γBL) has been found to result in electrolytes which remain uniform even upto very low temperatures and are suitable for devices operating at low temperatures. The variation of conductivity of liquid and gel electrolytes with polymer content, salt concentration and as a function of temperature has also been studied.

The electrochemical properties of ionic conducting membranes based on poly(acrylonitrile) (PAN), and the salt bis(trifluoromethane sulfone imide) lithium (LiTFSI) were studied. The influence of salt concentration on the ionic conductivity of these materials was illustrated that the best conductivity value was obtained for the highest salt concentration complexes at AN:Li = 1:1 ( 84 wt % of the salt), which indicates that the complex has entered the polymer-in-salt regime from salt-in-polymer regime. The dependence of temperature on conductivity shows that ionic transport mechanism changes from Arrhenius behavior to typical Vgel-Tammann-Fulcher (VTF) behavior when the complexes are P(AN)₂-LiTFSI and P(AN)₁-LiTFSI. It is in accordance with the results of XRD and vibration spectra. This finding demonstrates that a phase transition occurs as the content of lithium salt increases from P(AN)₃-LiTFSI to P(AN)₂-LiTFSI, which indicates this system is approaching a more disordered state.

PVDF-HFP based microporous films were prepared by phase inverse process. PVDF-HFP copolymer powder was dissolved in a mixture of acetone and a PVDF non-solvent (glycerol). The proportion of non-solvent was low enough to allow the dissolution and high enough to allow the phase separation during evaporation. The ratio of PVDF/acetone/glycerol in weight was controlled to 10-15/85-75/5-10. The membrane exhibit a spongy structure without clearly outlined skin layers when wet method is used, while it has skin if dry method is applied. The effects of solution composition, exposure time prior to coagulation and temperature of the coagulation bath on the micro-structure of prepared membranes were investigated. The porosity increase with the content of non-solvent, and decrease with the concentration of PVDF.

Four series of sodium ion conducting composite polymer electrolytes (CPEs) are described. The materials have been characterised in view of their properties needed for battery applications. The results on electrical conductivity, ionic transport number, electrochemical stability and mechanical properties are described. The conductivity has been correlated with the DSC data. The performance characteristics of the sodium cells with the optimised CPE and optimised plasticized CPE has been studied in terms of open circuit voltage (OCV), short-circuit current density and charge-discharge behaviour.

1,2,4-Triazole sodium salt and Dimethylbromobenzene, the redox shuttles, used as overcharge protection additives for lithium ion rechargeable batteries have been investigated. The results show that those redox shuttles have onset oxidation potential of 4.32V and 4.24V in 1MLiCLO₄+PC/DME (1: 1) electrolyte. They behave good electrical stability and do not bring any obvious bad influence on cells' performances under normal charge/discharge state or in presence in cells after the period of time. And they can effectively improve cells' charge/discharge efficiency when cells are overcharging.

In lithium ion batteries, the most suitable electrolyte graphitic for spinel LiMn₂O₄ cathode is PC series, and the most suitable electrolyte for anode is EC series. But we can only select one kind of electrolytes in the same battery. The compatibility of electrolyte with both the cathode and the anode were studied, and the methods for solving this problem were suggested.

The cycling performances of the cell with PEO based composite polymer electrolyte using ceramic filler, lithium metal anode, and LiNi_0.8Co_0.2O₂ cathode at 80°C have been examined. The best result was obtained in the electrolyte with the BaTiO₃ filler. The good cycling performance in the cell of Li/PEO₁₉Li(CF₃SO₂)₂N-BaTiO₃/LiNi_0.6Co_0.2O₂ was explained by the improved interfacial stability between the electrolyte and the electrode. The cycling performance of PEO based polymer electrolyte cell was influenced by the charge and discharge cut-off voltage. The electrochemical window of PEO₁₉Li(CF₃SO₂)₂N-BaTiO₃ composite electrolyte was estimated to be less than 4.0 V.

At present, a considerable attention is focussed on developing polymer electrolytes with good ionic conductivities at ambient temperatures and on all polymer lithium cells where both the electrolyte and the cathode are made of polymers. The present study is based on the synthesis of the gel electrolyte, PAN : EC : PC : LiCF₃SO₃ (Lithium Triflate - LiTf) and charaterization of lithium cells based on these electrolytes and polypyrrole (PPy) conducting polymer cathode. The composition of the gel polymer electrolyte which gives the maximum room temperature conductivity was found to be 15mol& PAN : 42mol& EC : 36mol& PC : 7mol& LiCF₃SO₃ and the highest room temperature conductivity obtained was 1.2 × 10⁻³ Scm⁻¹. The PPy electrode of thickness about 1 μm was made by electropolymerization of pyrrole incorporating a large anion, dodecyl benzene sulfonate (DBS). Cells with configuration, Li / PAN : EC : PC : LiCF₃SO₃ / PPy : DBS were fabricated and continuous charge-discharge cycling was performed between the voltages, 2.0–3.5 V vs Li. It was possible to obtain a specific capacity of about 45 Ahkg⁻¹ from these cells. Cells could be cycled successfully upto about 1000 charge/discharge cycles although a slow capacity decline was observed upon cycling.

Conventional techniques have inevitable defects in measuring chemical diffusion coefficient of lithium ion in host materials. However, using potential relaxation technique not only can determine the D₅ of lithium ion in host materials more accurately, but also can get the D₁ of lithium ion in the electrolytes simultaneously. In this paper, the theory of this technique has been demonstrated, and also the chemical diffusion coefficients of lithium ion in various carbonaceous materials have been discussed.

A silver nano-brush material has been prepared by alumina template and used directly as a working electrode in a Li/Ag nano-brush cell. It was found that a translucent film appears and covers on the surface of each Ag nanowire when the cell discharges to 0.2V. The film stick separated Ag nano-wires together into many bundles. In each bundle, Ag nano-wires were merged together. When the voltage of the cell drops to 0.0V gradually, the aggregation of Ag nano-wires becomes more serious. When the cell was charged to 2.0V, some Ag wires within a bundle were separated from the aggregation and the translucent film still exists on the surface of separated Ag nano-wires and the rest of aggregation. It is supposed that the film is well-known solid electrolyte interphase (SEI). The thickness of the SEI film ranges from 40nm to several nanometers.

Fuel cells utilizing proton-conducting polymer membranes (PEFC) are thought to be a most promising power source for environmentally acceptable electric vehicles. To date perfluorosulphonic membranes (Nafions) have been used almost exclusively for this type of fuel cells. However, the high price of such membranes is a great problem. Moreover, the operating temperature of most PEFCs is limited to 100°C or lower due to heat-resistance limitations of the membranes, though higher temperature is desirable for some reasons, for example, that the polarization could be reduced and the water balance control in fuel cell system would be easier. For fuel cells fed with reformed gas, higher operation temperature is especially needed to protect catalysts from the poisoning by carbon monoxide. In addition, the total efficiency of a system including a reformer could be improved because recovery of heat would be easier at elevated temperature. Therefore, some alternative materials including organic/inorganic composites have been studied to develop a less expensive and more heat-resistive membrane…

Note from Publisher: This article contains the abstract only.

The protonic conduction in non-perovskite-type oxides under hydrogen-containing atmosphere at elevated temperatures studied in our laboratory is summarized.

Pyrochole-type Ln₂Zr₂O₇ (Ln = La, Nd, Sm, Gd and Er) showed protonic conduction when Y was partially substituted for Zr. EMF behavior of hydrogen concentration cells and electrochemical hydrogen pump using this kind of oxides as an electrolyte supported that the conduction was purely ionic.

La₅₈WO₁₁₇, with fluorite-related structure showed protonic conduction in hydrogen containing atmospheres. Besides the electrochemical methods, the H/D isotope effect on conductivity suggested the protonic contribution to conduction, although the transport number of proton estimated from the EMF of concentration cell was less than unity. La₅₈WO₁₁₇ showed good chemical stability even in reducing atmospheres.

The conductivity of Ba₃(PO₄)₂ was enhanced by partial substitution of K for Ba. The ionic transport number in hydrogen containing atmosphere in Ba_3-xK_x(PO₄)_2-x/3 was unity. LaBO₃ also showed the sign of protonic conduction under same conditions as above.

Solid oxide fuel cell program in Shanghai Institute of Ceramics, Chinese Academy of Sciences, has been established to develop materials(electrolyte, electrode, interconnect and high temperature sealant), planar stack structure and fabrication techniques. Main achievements of the program are emphatically reported with regard to electrolyte membrane preparation, cathode material system synthesis, interconnect fabrication as well as stack structural design.

Operation performances of a two-cell and a ten-cell planar SOFC stacks with cell size of 40×40mm² are described. The ten-cell stack was tested at 1000°C with a power output of up to ten watts and a power density of around 100mW/cm². Future work has been doing to develop a planar SOFC stack of hundreds watts with cell size of 100×100mm², and an electrode support cell system with thin electrolyte below 20 μ by various fabrication processes.

With adding of nano-Al₂O₃, nano-4YSZ power was used as raw materials for pressureless sintering. The experimented results show that 4YSZ ceramic can be sintered at lower temperature adding some nano-Al₂O₃. 99% of theoretical density was obtained for nano-4YSZ containing 1.0wt% of additives sintering at 1200°c for two hours.

The hardness was 83HRA. The activation energy increases and conductivity deceases with additions of nano-Al₂O₃.

LSGM (La_0.9Sr_0.1Ga_0.8Mg_0.2O₃) and LSM (La_0.9Sr_0.1MnO₃) are attractive electrolyte and cathode materials, respectively, for the intermediate temperature solid oxide fuel cells. Since both materials are based on perovskite structure, the reaction between them is easily expected. In this study, various compositions of xLSM-(l-x)LSGM (x = 0 ∼ 1) system were prepared to identify the possible reaction product and to see their effects on the electrical conductivity. Powder compacts were prepared by using the solid-state reaction method and sintered at 1500°C for 6 h.

The phase, analyzed from XRD patterns, changed from single-phase cubic at x = 0 ~ 0.16 to hexagonal at x = 0.2 ~ 0.5 and finally to orthorhombic at x = 0.60 ~ 1. The electrical conductivity of LSGM, measured by 4-probe d.c. method between 430°C and 910°C in air, decreased with increasing LSM content in the cubic composition range, showing the harmful effect of LSM on the electrolyte conductivity. The conductivity decrease was explained by the increase in the activation energy and the decrease in the charge carrier concentration. Above x = 0.16, the conductivity increased rapidly, showing the effect of percolation by the conductive hexagonal and orthorhombic phases.

The chemical reactivity of the perovskite-type oxides, RE_0.6Ca_0.4Mn_0.5Co_0.5O_3-δ (RE = La, Pr, Nd, Sm and Gd), and yttria stabilized zirconia (YSZ) has been examined. Powder mixtures of perovskites and YSZ were annealed at 1200 °C for 24h in air. The formation of CaZrO₃, was identified by X-ray diffraction analysis as a reaction product for all compositions in RE_0.6Ca_0.4Mn_0.5Co_0.5O_3-δ. The bond-valence model was used to discuss the chemical reactivity of perovskites and YSZ. Furthermore, the amount of CaZrO₃ formed was greater than 17% (I_product/I_YSz). The present study also identified a shift in the lattice parameter of cubic YSZ solid solution after reaction, corresponding to a lattice expansion.

Novel ceramic composite electrolytes based on doped ceria-inorganic salt/hydroxide were developed and demonstrated great potential for intermediate temperature (IT, 400-800°C) solid oxide fuel cells (ITSOFCs). The inorganic salts or hydroxides used here are mainly alkaline/alkaline earth chlorides/fluorides/ hydroxides. The co-existence of both H⁺ and O²⁻ conduction was found in these composite electrolytes. This makes the transport mechanism of both charge carriers more complex than conventional electrolytes. Fuel cells based on these composite electrolytes show good performance at intermediate temperatures. A peak power density of 200-400mW/cm² at a current density of 400-800mA/cm² was achieved at 400-750°C. This makes them new candidates of electrolytes for future ITSOFCs.

Novel ceramic fuel cells based on CeO₂-salt (e.g. Li₂CO₃K₂CO₃) composite electrolyte, operating at 480~550°C, was studied. Various FC construction techniques and electrode materials were investigated. Ni-Ce_0.8Gd_0.2O_1.9 (GDC) is employed as the anode, while Ag and some perovskite materials, such as La_0.8Sr_0.2MnO₃, La_0.6Sr_0.4Co_0.2Fe_0.8O₃ and La_0.6Sr_0.4CoO₃, are chosen as the cathodes. Among them, the fuel cell, using Ni-GDC and La_0.6Sr_0.4CoO₃ as the anode and the cathode, has shown the best performance, 750 mAcm⁻² at 0.4 V was achieved.

The performance of a hydrogen-oxygen fuel cell using BaCe_0.9Y_0.1O_3-α as a solid electrolyte was investigated in the temperature range of 600 ~ 1000°C. It was found that the maximum short-circuit current density and the maximum power output density at 1000°C were about 980 mA cm⁻² and 0.22 mW cm⁻², respectively. The performance was significantly higher than those reported so far of the other solid oxide cells based on BaCe_0.9M_0.1O_3-α(M = Y, Sm, Gd, Yb, Nd, etc.).

Samples of BaZr_1-xY_xO_3-α(x = 0.02, 0.05, 0.10 and 0.15) were prepared by solid state reaction method. XRD was used for the identification of the single perovskite phase and SEM for the estimation of the average of grains size. The porosity of each sample was measured and samples with x = 0.02 and x = 0.05 were found to have porosity less than 4%. By means of electrochemical cells we demonstrated that the BaZr_0.95Y_0.05O_3-α sample is a protonic conductor. The sample exhibited a negligible oxide ion conduction when it was used as electrolyte in the oxygen concentration cell. Its bulk conductivity under wet N₂ was higher than that under dry N₂. The bulk conductivity measurements of BaZr_1-xY_xO_3-α undedr different atmospheres showed that the conductivity was dependent on water vapor partial pressure P_H2O at 500 ≤ T ≤ 900°C and on oxygen partial pressure P_O2 only at 800 ≤ T ≤ 900°C. We also verified the chemical stability of BaZr_0.95Y_0.05O_3-α under CO₂ at 650°C.

Pr_1-xM_xGaO₃(M = Ca, Sr, x = 0, 0.05, 0.1, 0.2) oxides were synthesized using a standard solid state technique. An orthorhombic structure was found from XRD data. The limit of solid solution is x=0.1 for Ca/Sr doped at A sites. Sr/Ca-doping increases the oxygen ion conductivity and decreases the activation energy of samples. Pr_0.95Sr_0.05GaO₃ has the highest conductivity of 0.022Scm⁻¹ at 800°C and Pr_0.95Sr_0.05GaO₃ has the lowest activation energy of 24.19KJ/mol in all the samples. With temperature increasing, the oxygen ion transport number of samples increases. The conductivity of these samples is mainly ionic.

DC polarization measurements using ion-blocking electrode were applied to La_0.9Sr_0.1InO_3-δ as functions of temperature and oxygen partial pressure in order to determine the electronic conductivity. A new model was proposed to interpret the Hebb-Wagner polarization curves for ion blocking measurements. The electron and hole conductivity has been obtained respectively. Between 600 and 800°C at oxygen partial pressures of 1 to 0.05atm the electronic conductivities are found to be: and

La_0.9Sr_0.1InO_3-δ was prepared by sol-gel process that involves nitrates and ethylene glycol. The XRD patterns indicate that a single perovskite oxide formed after sintered at 1400°C for 12h. Thermal analysis (DTA/TGA) reveals that endothermic peak corresponds to the dehydration when the gel was heated at 150°C. The exothermic peaks at 350 and 370°C may be related to the decomposition of metal chelates. TEM observations show that the agglomerated particles have an average 250nm size after calcined at 600°C, SEM results reveal that the final product has less pores and the mean particle size is 1μ. More dense and well crystallized sample with higher electrical conductivity was obtained by sol-gel method.

The properties of (ZrO₂·Y₂O₃·Gd₂O₃) slip with intermediate diameter (The raw materials bellow 1 μm in diameter exceed 60wt%) were studied in this paper. The slip casting was performed using plaster mold. It is found that several factors, including the pH value of suspension slip, the concentration of dispersing agent (PAA) and Arab gum etc., have effects on the stability and mobility of the slip. Sick suspending slip with good suspension, small sedimentation volume, high solid volume fraction can be synthesized by modifying the prominent factors and optimizing parameters that affect the slip seability and the property of final product, which resulting in high green cast density (3.80g/cm³). The optimized powder (ZrO₂·Y₂O₃·Gd₂O₃) and slip can enhance the point diffusion and the microstructure of the final production during the firing process. On the other hand, the enhanced plaster mold with good properties was obtained, which can be used up to 40~50 times.

Yttria-stabilized tetragonal zirconia polycrystalline (TZP) membranes were fabricated by tape casting. The micro-structures, the electrical and mechanical properties of the membranes were all examined. An operation test was conducted on a planar single cell, which was based on the TZP membrane. For pure H₂ as fuel and pure O₂ as oxidant a maximal power density of about 108mW/cm² was achieved when the single cell was operated at 950°C. The single cell performance was very stable during the long period of the operation test.

Nanocrystalline ZrO₂(4Y) powders are sintered at ultra-high pressure (4GPa) for 2 min at 1000°-1200°C. Microstructure, phase relation, densification and conductivity of the sintered ZrO₂(4Y) are investigated. The test result shows that the relative density of undamaged sintered ceramics body i s above 99.3%. The crystal grains grow to 40-70nm. The C_ta_t⁻¹ of the t-ZrO₂ sintered at high pressure is smaller than it sintered at normal pressure. The color of the sintered ZrO₂(4Y) is brown, dark gray and black. The conductivity of the ceramic samples sintered at high pressure is lower than it sintered at normal atmosphere. The influence of additive on the properties of the sintered ZrO₂(4Y) through adding some nano-Al₂O₃ powder are investigated too.

8mol% yttria-stabilized zirconia (YSZ) membranes with additions of 0~4.5 vol% Al₂O₃ powder were fabricated by tape casting. The SEM photographs show that alumina particles were dispersed homogeneously in the sintered membranes. The relative density reached a maximum of 96.4% of theoretical with increasing Al₂O₃ concentration up to 3 vol%. The electrical conductivity at 800°C increased slightly with 1.5 vol% alumina and then decreased with further alumina addition. Also with 1.5 vol% alumina addition, the strength of single YSZ membranes tested at room temperature (RT) increased by 70%.

A novel process, namely phase-transfer-separation (PTS) process, which is convenient in the separation of solid and aqueous phase was applied in the current study to prepare nanosized 8mol% yttria stabilized zirconia powders. Two kinds of surfactants-SPAN80 and LAS were used to enhance the solid-liquid separation process. The terminal product has a cubic phase, and average particle size estimated from TEM image is about 20-30 nm. The contents of impurity ions such as Na⁺ and Cl⁻ are as low as 7.05 ppm and 141.4 ppm respectively. The recovery efficiency of a main raw material, petroleum ether, is 80%. From the results obtained, it is reasonable to conclude that PTS is a kind of efficient and economical process for the preparation of nanometer ceramic powders.

In this paper, Al₂O₃/8YSZ with different amount of CeO₂ (from lwt%~10wt%) are synthesized by a ceramic method, and sintered at 1600°C for 20h. Impedance analysis shows that the conductivity of the samples is developed by the doping of CeO₂. SOFC performance of using these samples as electrolytes is better than pure YSZ, and its maximum output is about 0.16W/cm² when the doping amount is 10wt%. From the X-ray diffraction patterns within the range (doping CeO₂ from lwt%~10wt%), there is only a single cubic phase present, and the grain size is bigger than pure YSZ.

The microstructure and the ionic conductivity of the Al₂O₃ - ZrO₂(Y₂O₃) eutectic composites prepared by directional solidification are described. An influence of the high temperature annealing on the electrical conductivity is studied.

Molecular dynamics simulation was performed to investigate the vibrational property of yttria stabilized zirconia (YSZ). Phonon density of states was calculated for 8-20 mol% YSZ. The results well explained the behavior of measured heat capacity. It was found that the relaxation in the anion sublattice around the vacancy changes the phonon density of states. The relationship between the vibrational property and defect structure of YSZ was discussed.

The structures and dehydration of amorphous hydrous zirconia was studied by Infrared Speclroscopy (IR), X-ray Diffraction (XRD), Differential Thermal Analysis(DTA) and Thermogravimctry (TG). We found some metastable phases of amorphous hydrous zirconia. Their compositions are different. They have different O-H and Zr-O bonds and different molecular symmetry. The different structures of amorphous hydrous ZrO₂ dehydrated to form different structures of amorphous ZrO₂, and further crystallized to different crystalline ZrO₂. An explanation based on the nature of the Zr-O bond and hydroxyl group has been proposed.

The nanostructure and structural change of zirconia precursor in its dehydration and crystallization process were studied by the Positron-Annihilation Spectroscopy. X-ray Diffraction (XRD), Differential Thermal Analysis (DTA), Thermogravimetry (TG) and Infrared Spectrometer (IR). A great number of subnanometer voids in about 0.4 nm diameter voids in zirconia precursor have been recognized. It indicated that the buck was a network structure. The density of network in the dehydration process had been studied. After crystallization, some hydroxyls still left in the crystals and form doped hydroxyls. They stabilized the cubic structure of zirconia.

The microstructure of zirconia precursor have been studied by positron-annihilation spectroscopy, infrared absorption spectra (IR), X-ray diffraction (XRD) and TG. All these showed that the zirconium structures had great relationship with the pH of origin sol when we prepared zirconium powder.

It was found that the atomic hydrogen permeation, J_H, in (ZrO₂)_0.85(CaO)_0.15 was enhanced by H₂O, P_H2O^out(0.0070 − 0.0388/ atm), which was humidified in the hydrogen source gas(200/cm³min⁻¹, P_H2^Out: 0.046 − 0.580 / atm in N₂), at 1400-1800 / K. While the excess water hindered the hydrogen permeation. The specimen was an end closed tube which was supplied by Nikkalo Corp. The source gas and Ar gas(21.4 / cm³min⁻¹, P_H2Oⁱⁿ≤ 5×10⁻⁷, P_O2ⁱⁿ ≤ 1×10⁻⁷/atm) was let flow to the outside and the inside, respectively. The mixed gas from the outlet of inside was analyzed by a gas chromatograph and determined the permeated hydrogen partial pressure, P_H2ⁱⁿ. Log J_H was almost proportional to log P_H2O^out, log (P_H2ⁱⁿ) and reciprocal temperature, respectively.

Ceramic/salt composites have been extensively tested as the electrolytes for SOFCs recent years. But the thermodynamic stability of the salt involved in fuel environment would govern the long-term performance of the cell. Thermodynamic calculation shows that Li₂SO₄ based salts are not stable in hydrogen and they may be reduced to form H₂S and LiOH, which was proved by experimental observation. Fluoride and chloride based electrolytes including LiF, NaF, CaF₂, BaF₂ and NaCl etc. are newly explored to exhibit both proton and oxygen ion conduction and tested as electrolytes for H₂/O₂ fuel cells. Those halides are quite stable according to the very positive Gibbs energies of their reactions with hydrogen/steam. However, it will gradually consume and hence can not stand long term in the fuel cell environment due to undergoing sublimation in the gas flow system. This can be, however, avoided if some measures are taken to keep an appropriate partial pressure of HF or HCl at the reaction chambers.

N, N-dimethyl pyrrolidinium was synthesised and doped into the plastic crystal matrices of the alkylmethyl pyrrolidinium imides to obtain solid, hydroxyl ion conductive materials. This work has shown that the conductivity of these alkaline materials was affected by several factors, including the cation structure, hydroxide content, moisture content and temperature. The highest conductivity for these solid conductors was obtained in the range of 2×10⁻⁴ S.cm⁻¹ at room temperature. The relationship between conductivity and temperature, material composition, and measurement conditions, as well as the thermal behaviour for these alkaline materials are discussed.

γ- LiAlO₂, is a potential candidate for the use as ceramic separator in molten carbonate fuel cells. A combustion synthesis technique, the glycine-urea-nitrate process was described and investigated in this paper. A combination of the aqueous solution of glycine-urea and metal nitrates was employed as a precursor for the process. Gels were formed while the solutions were evaporated. Further heating caused the precursor to autoignite. The experimental results of phase analysis, particle morphology and particle size analysis indicated that pure γ- LiAlO₂ with fine crystalline and high reactivity could be obtained by the combustion technique.

A new deoxidation technology using ZrO₂ solid electrolyte has been developed for metallurgical process, in which no any inclusion will be introduced after deoxidation and a clean metal will be obtained. This new technique is simple and flexible; it can be used in various cases in metallurgical process. A theoretical formula has been used to describe this process and a good agreement has been reached between experiment and theoretical calculation.

The new type of inorganic membranes under development is dense ion-transport ceramic membranes, which are mainly based on either oxygen ionic conducting or proton conducting property and permeable to oxygen or hydrogen, respectively. These ion-transport ceramic membranes have great promise in many potential high-tech applications such as oxygen or hydrogen separation, solid oxide fuel cells, catalytic membrane reactors and electrochemical sensors. The present paper describes the current trend of the research and development of these novel membranes and the research activities and results mainly at the authors' lab

Zirconium phosphates (ZrP) with layered structure have been studied extensively over last 40 years because of their ion exchange, intercalation, and ion conductivity properties. The present paper reviews the preparation methods and exchange behavior of Zr(HPO₄)₂.H₂O, with special regards to its application in the development of antibacterial ceramics. The conductivity properties of ZrP salts are summarized and a new route to prepare commercial AgZr₂(PO₄)₃ antibacterial powders is reported.

The MgO-PSZ tube was prepared by Powder Injection Molding. The final sintered rube was assembled into oxygen cell, then tested in our lab and Wuhan Iron and Steel Company. The results showed the thermal shock resistance of MgO-PSZ matrix was enough to determinate the active oxygen concentration in the steel melt. The reproducibility of the measured EMFs and the stability of the curve were very well. We discussed the structure of the tube by means of SEM and XRD. In addition, we compared the characteristics such as the density and phase ratio of our product with that of Shijiazhuang Maple Wood Sensor Company. At last, we found the Powder Injection Molding technology is very suitable for the manufacture of ZrO₂ based oxygen sensor.

This paper presents the application of the solid state ionic material as electrolyte to chemical sensors. Solid-state gas potential sensors based on four types of ionic conductors and their general principle, structure and performance are introduced for detecting O₂, H₂ and C₂H₄ at room temperature, attention is focused on the selection of electrolyte and catalytic electrode and the preparation method of composite electrodes. The experiments showed that these sensor characteristics depend on the catalytic activity of electrode material used, electrolyte properties and the preparation method of composite electrode assemblies. The kinetics of oxygen reduction was also discussed.

Selective decomposition of nitrogen monoxide (NO) in the presence of oxygen was studied by using an electrochemical cell composed of yttria-stabilized zirconia (YSZ), Pt electrodes and of surface oxide layer. It was shown that the covering of sensing electrode (cathode) by oxide with high catalytic activity for adsorption and decomposition of NO and low activity for O₂ adsorption decreased the oxygen gas pumping through the cell and increased the NO decomposition. It was found that the NiO-YSZ mixed oxide is the most excellent material for sensing electrode. The phenomenon of self-organising of the microstructure of NiO-YSZ mixed oxide sensing electrode during the process of operation of the cell was observed and investigated. It was shown that self-organising of microstructure of sensing electrode leads to the improvement of the properties of the electrochemical cell for NO decomposition and to the increase of the value of the current efficiency coefficient. The microstructure of the NiO-YSZ mixed oxide used as a sensing electrode was investigated and the mechanism of selective NO decomposition in the presence of oxygen has been proposed.

The transition metal oxide thin films have been used in electrochromic devices, solid state microbatteries and display panels. The materials in this category that have attracted most of research interest are MoO₃, WO₃ and IrO_x. Molybdenum oxide films shows some common properties with tungsten oxide. This paper reports the preparation of MoO₃, and its surface structure properties. The starting materials were MoO₃ powder (with purity of 99.95%) in pellet form of about 13-mm diameter. Thin films were deposited by electron beam evaporation on glass substrates at various temperatures under a partial pressure of about 10⁻⁵ mbar. The deposited films were then annealed in oxygen at 100 −200°C for 3 hours. The thickness of the films were 800-1200 Å. The optical measurement was made over the wavelength range of 300 nm to 800 nm using a spectrophotometer. The Van de Pauw technique was employed to measure the electrical resistivity of the films. The films formed at 100 °C are amorphous with conductivity of about 2.5 × 10⁻⁵ Ω⁻¹ cm⁻¹, green in colour. The topography of MoO₃ films based on the atomic force images will be described in details. The annealing process has changed the surface morphology of samples hence its electrical property.

Amorphous and crystalline tungsten trioxide (WO₃) electrochromic films of 240 to 400 nm thick were grown on single crystal silicon wafer and ITO-coated glass substrates by reactive sputtering from a tungsten target. The electrochemical properties of the films were characterized by cyclic voltammetry between −1.0 ~ +1.0 V in 1M LiClO₄/PC solutions. The Cary 500 measurements of the films indicated remarkable changes in the transmission and reflection in visible and infrared regions due to Li⁺ ions injection/extraction. The emissivity of the WO₃ films on the Au substrates was modulated in the range from 0.042 to 0.450. The results showed that the crystalline WO₃, films obtained here have excellent thermal emissivity modulation, enabling fabrication of electrochromic devices that can freely change their optical properties under a slight voltage pulse.

Electrochromic(EC) coatings, thin films that change their optical absorptance as a function of injected ions (typically H⁺ or Li⁺ species), is an area of research and development that has received attention from academia, industry and government laboratories. In this paper a new hydrogenation technology and its fabrication process are put forward, the study on the resistivity, surface morphology, the crystal analysis, and the electrochromic properties is also performed, thus the optimum process is defined. In doing that, there is an important meaning for preparing the all-solid electrochromic devices.

Electrochromic windows could reduce air-conditioning costs by being darkened to absorb sunlight and reject unwanted solar heat. These windows change their color and light transmissivity due to the action of an electric field and can change back to the original state by a field reversal. To save the cost, the electrical power may be supplied by a solar cell that integrated with the electrochromic window in a single device. This paper reports the potential of using titanium oxide, TiO₂ as solar cells and as electrochromic windows. The TiO₂ films were deposited by screen-printing a paste, consisting of TiO₂ particles and an organic binder, onto ITO-covered glass substrates. Then the films were tempered at 400 °C to bum out the organic parts. A solar cell of ITO/TiO₂/electrolyte/ITO was fabricated using a mixed ammonium iodide and iodine solution as electrolyte. The cell was illuminated through the TiO₂ film. The cells showed rectifier properties in the dark and produced electrical current when illuminated. The short circuit photocurrent and the open circuit voltage of the cell in a 100-mW/cm² tungsten light source were 2.3 μA and 17.0 mV respectively. The electrochromic behavior of the TiO₂ films in a lithium perchlorate solution was examined. When the electrochromic film cell was given a forward bias potential of 5.0 V, the original colorless TiO₂ film immediately changed to brown. The color of the film bleached to the original when the applied potential was reversed.

Porous nickel oxide were prepared by hydrolysis of nickel acetate and heated in air at 300 °C. The resulting nickel oxide behave as an electrochemical capacitor with a specific capacitance 240F/g electrode. These nickel oxide maintain high utilization at high rates of discharge (i.e., high power density) and have excellent cycle life. The NiOH/KOH/C supercapacitor was also introduced briefly in this paper. This kind of supercapcitor have promising potentials in portable telecommucations, uninterruptable power supplies, and battery load leveling applications.

The adsorption of anions on platinum electrode was determined by electrochemical impedance spectroscopy in H₂SO₄ solution. The results indicate that addition of Cl⁻ may increase adsorption capacitance largely, while F has little influence on adsorption capacitance. The results of cyclic voltammetry (CV) show that the methanol oxidation peak current decreases slowly with increase the concentration of F, but drastically with the increase of Cl⁻ concentration.

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