Ceramic Electrolytes for All-Solid-State Li Batteries

The following sections are included:

• Preface
• Contents

A ceramic material is an inorganic and non-metallic solid material that is composed of metal, non-metal and metalloid atoms bound by covalent or ionic bonds. The ceramic materials can range from crystalline and semi-crystalline to amorphous (glass) depending on the ordering of the structure. Generally, the ceramic materials have a high melting temperature, poor thermal and electrical conductivities, high hardness and low ductility. Also, the ceramic materials are lighter (less dense) than metals and heavier than polymers. They normally possess high thermal resistance, but low resistance for heat shock. Because most elements and types of bonding, and all range of crystallinity can comprise the ceramics materials, a lot of materials such as oxide, nitride and carbide materials are included in this category. Accordingly, the ceramic materials have been employed in a wide range of applications, such as in the manufacturing of bricks, tiles, dishes and vases…

Recent rapid progress and growing efforts to use clean and renewable energies have strongly required to urgently develop energy storage devices with high energy and power densities [1]. Electrochemical energy storage devices such as batteries and capacitors match this requirement because they can efficiently store and deliver energy when it is needed. Particularly, Li battery is expected to possess high energy density compared with other batteries like lead-acid battery, and so it has been thought to be a promising battery to fulfill this requirement [2]…

Ion conduction in solids has been known for more than a century [1]. The first electrical conductive solid was discovered by Michael Faraday who, in 1883, reported that the electrical conductivity of Ag₂S was largely increased with increase in temperature [2]. Additionally, he discovered similar behavior in several other inorganic solids such as PbF₂, in 1838 [3]. This behavior was difficult to explain at that time because the behavior was opposite to that in metallic phase. Later, Hittorf investigated the conductivity of Ag₂S and Cu₂S and concluded that these materials had an electrolytic conduction mechanism [4]. Then, in 1884, Warburg proved that sodium ion could migrate through the solid, which overturned the conclusion of Arrhenius that neither pure salt nor pure water can be a conductor but that only salt dissolved in water…

The following sections are included:

• Structural Fundamentals of Ion Conductive Ceramics
• Ion Conduction Inside the Crystal
  • Defect
  • Hopping model
• Ion Conduction at the Interface
  • Space charge effect
  • Percolation effect
• Strategies for Lithium Conductivity Enhancement
• References

The Crystalline electrolytes possess a rigid skeleton composed of complex anion polyhedra that are long-range ordered. Li-ion can migrate in the skeleton with low activation energy. Li-ion conductivity of crystalline electrolytes is generally 1 to 2 orders higher than that of amorphous/glass electrolytes. However, preparation of a single-crystal solid electrolyte is costly and consumes a lot of energy and time. Therefore, polycrystalline solid electrolytes have usually been used. In the polycrystalline electrolytes, grain-boundary conductivity is generally lower than that in the crystal (bulk conductivity), particularly for Li₃N, β-Al₂O₃ and perovskite compounds which have 2D anisotropic conduction path. On the other hand, 3D ionic pathways can theoretically avoid the conductivity degradation at the grain boundaries in polycrystalline ceramics. Many polycrystalline Li-ion conductors have been researched so far. Among them, oxide and sulfide Li-ion conductors have been highly anticipated to serve as solid electrolytes. In this chapter, crystalline oxide and sulfide Li-ion conductors are reviewed.

The following sections are included:

• Amorphous/Glass Li-ion Conductor
  • Oxide glass
  • LiPON
  • Sulfide glass
• Glass-Ceramic Li-ion Conductor
• References

It is well known that Li batteries are an attractive energy source for portable electronic devices (e.g. laptop computers, cameras, toys, mobile phones, and so on) and transport applications. However, there are still many issues, such as safety issue. All-solid-state battery with a ceramic Li-ion conductor as a solid electrolyte has the following potential advantages [1, 2]:

• absence of electrolyte leakage,
• high safety because of absence of flammable liquid electrolyte,
• absence of problems relating to vaporization of liquid electrolytes,
• absence of phase transition of the electrolyte at low temperature, which improves low temperature performance, and
• ease of miniaturization

In addition, all-solid-state batteries usually have excellent storage stability and long life due to suppression of side reactions because only Li-ion can move inside the solid electrolyte…

All-solid-state Li-ion battery and Li-air battery are expected as the next generation of energy storage devices. To successfully fabricate all-solid-state battery and Li-air battery, Li-ion conductors should possess high ionic conductivity, electrochemical stability and wide stable potential range. Although there are many Li-ion conductive ceramics which are capable of being used as a solid electrolyte for the all-solid-state battery, all-solid-state battery with Li-ion conductive ceramics has not yet appeared on the market, except LiPON-based thin-film battery. The reason for that is thought to be lack of knowledge of interface between electrode and electrolyte and of the ceramic process technique. The property of the interface is critical to determine the performance of the all-solid-state battery; however, this is still not clear enough. The properties of the interface need to be clarified in detail. For that, SEM observation with EDS mapping [1–3] and electrochemical impedance technique [4] and other such techniques have been used (Fig. 8.1). Li atoms are not sensitive to EDS mapping, and even with these techniques it is difficult to detect the interface at the atomic scale. These restrictions of the characterization techniques must be solved. Recently, spatial-resolved electron energy-loss spectroscopy (EELS) combined with TEM was used to characterize the electrode/electrolyte interface at the atomic scale [5, 6] (Fig. 8.2). …

The following section is included:

• Index