Journal of Molecular and Engineering Materials

In this paper, hierarchical Li₄Ti₅O₁₂ microspheres were successfully synthesized in a large scale via a facile hydrothermal route. X-ray diffraction, field emission scanning electron microscopy and transmission electron microscopy were used to characterize the obtained Li₄Ti₅O₁₂ microspheres and the results indicate that the monodispersed Li₄Ti₅O₁₂ microspheres with ca. 2 μm in diameter was assembled by well-crystalline nanoparticles. Electrochemical analysis indicated that the Li₄Ti₅O₁₂ microspheres have superior rate capability and cycling performance. At the charge–discharge rate of 0.2, 1, 2, 5, 10 and 20 C, the discharge capacities of Li₄Ti₅O₁₂ microspheres are 169.2, 163.5, 158.3, 136.4, 117.6 and 94.3 mAh g⁻¹, respectively. Excellent capacity retention of 98.7% was achieved after 100 cycles at 1 C rate and it can still maintained 91% even at high rate of 10 C.

In this paper, SnO₂ nanospheres have been synthesized via a surfactant-free solvothermal reaction followed by a heat treatment. CV results demonstrate that the formation of Li₂O is partially reversible. Moreover, electrochemical measurements indicate the preferable electrochemical properties of SnO₂ nanospheres.

Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode materials for Li-ion batteries were synthesized by a facile sol–gel method followed by calcination at various temperatures (700°C, 800°C and 900°C). Lithium acetate dihydrate, manganese (II) acetate tetrahydrate, nickel (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate are employed as the metal precursors, and citric acid monohydrate as the chelating agent. For the obtained Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ materials, the metal components existed in the form of Mn⁴⁺, Ni²⁺ and Co³⁺, and their molar ratio was in good agreement with 0.56 : 0.16 : 0.08. The calcination temperature played an important role in the particle size, crystallinity and further electrochemical properties of the cathode materials. The Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ material calcined at 800°C for 6 h showed the best electrochemical performances. Its discharge specific capacities cycled at 0.1 C, 0.5 C, 1 C and 2 C rates were 266.0 mAh g⁻¹, 243.1 mAh g⁻¹, 218.2 mAh g⁻¹ and 192.9 mAh g⁻¹, respectively. When recovered to 0.1 C rate, the discharge specific capacity was 260.2 mAh g⁻¹ and the capacity loss is only 2.2%. This work demonstrates that the sol–gel method is a facile route to prepare high performance Li[Li_0.2Mn_0.56Ni_0.16Co_0.08]O₂ cathode materials for Li-ion batteries.

In this paper, we developed an intriguing ion-exchange reaction to synthesize Ni-doped titanate nanotubes (Ni-Ti-NTs), and utilized the sample as an appealing pseudocapacitive electrode for electrochemical capacitors (ECs). The energy storage mechanism of the resulting Ni-Ti-NTs electrode in alkaline KOH aqueous electrolyte was further tentatively proposed. Compared with the pristine titanate nanotubes (Ti-NTs), Ni-Ti-NTs with rich porous channels possessed much better electronic conductivity and larger specific surface area, rendering the electrons and OH⁻ ions easily contact the Ni species uniformly distributed on their surfaces for efficient energy storage at high rates. Remarkably, the SC of the Ni-Ti-NTs electrode increased with further cycling, and even reached a SC of 278 F g⁻¹ at a current density of 2 A g⁻¹ after 7500 charge–discharge cycles without relaxation. The prominent electrochemical performance demonstrated that the Ni-Ti-NTs would be a promising candidate and/or even excellent support for other electroactive materials for advanced ECs application.

We report a facile chemical vapor deposition (CVD) method to grow silicon/carbon (Si/C) microspheres on commercial graphite microsphere (GMs) surface to prepare Si/C/GMs composite anode materials for Li-ion batteries. The CVD synthesis is conducted at 900°C using methyltrichlorosilane (CH₃SiCl₃) as both the Si and C precursor, which is a cheap byproduct in organosilane industry. The samples are characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy and X-ray photoelectron spectroscopy. It is found that the obtained Si/C/GMs composites are composed of Si nanocrystals, amorphous carbon and GMs. The CVD time significantly influences the morphology and electrochemical performance of the Si/C/GMs composite materials. The Si/C/GMs composite materials prepared at CVD condition of 900°C for 4 h possess improved electrochemical properties, showing a discharge capacity of 821.4 mAh g⁻¹ at a rate of 50 mA g⁻¹, and a good cycling performance (i.e., a reversible capacity of 565.2 mAh g⁻¹ is retained after 50 cycles). The enhanced electrochemical performance is attributed to the formation of Si/C microsphere network among GMs, which increases the electronic conductivity and is able to buffer the large volume changes of Si during lithium ion insertion/extraction.

In this paper, we report an interesting approach for efficient synthesis of uniform sub-micrometer carbon supported Fe₃O₄ hollow spheres. Fe₃O₄ precursor was first coated on the surface of sulfonated polystyrene hollow microspheres. Then, the precursor and sulfonated polystyrene hollow microspheres were converted into Fe₃O₄ and carbon hollow spheres when heated at 550°C in N₂ atmosphere. The obtained Fe₃O₄ @ carbon hollow microspheres exhibit enhanced lithium storage properties compared with Fe₂O₃ hollow spheres as anode materials, delivering a reversible capacity of 612 mA hg⁻¹ after 50 cycles at a high current density of 400 mA g⁻¹.

Novel TEMPO radical grafted PANI [polymer (3)] was synthesized from 2,5-dicarboxyaniline by two-step process, and investigated with Fourier transform infrared spectroscopy, electron spin resonance spectra, thermogravimetric analysis, scanning electron microscopy, cyclic voltammograms, and galvanostatic charge–discharge techniques. The polymer (3) shows six-electron redox reaction process in the voltage ranges of 2.0–4.0 V versus Li⁺/Li. A high specific capacity of 156 mA h g⁻¹ is obtained in the experiment, close to half of the theoretical capacity of the polymer based on six-electron redox reaction (330 mA h g⁻¹. The polymer (3) also exhibits good rate capability and cycle life. The excellent electrochemical properties benefit from fast redox reaction of nitroxy radical and conductive polyaniline nanotubes structure.