Gholam-Abbas Nazri

Solid State Batteries: Materials Design and Optimization

Preface. 1. Design and Optimization of Solid-State Batteries. 2. Materials for Electrolyte: Crystalline Compounds. 3. Materials for Electrolyte: Fast-Ion-Conducting Glasses. 4. Materials for Electrolyte: Thin Films. 5. Polymer Electrolytes. 6. Materials for Electrodes: Crystalline Compounds. 7. Materials for Electrodes: Amorphous and Thin-Films. 8. Applications of Solid-State Ionic Materials. Subject Index.

Applications of solid-state ionic materials

Solid-state ionic materials have been extensively developed and applications of solid electrolytes as well as insertion compounds have begun to converge into a coherent field during the last 10 years. Various designs of working devices are outlined in this chapter with the emphasis on all solid-state configurations. The large number of references reflects the great interest of researchers in energy storage devices, sensors, and optical and other electrochemical applications of solid-state ionics. For most types it is mentioned whether they are commercially available, items of intense current development, or one of the hot new research items.

Materials for electrodes: Amorphous and thin-films

Until now, the materials investigated with a view to finding suitable intercalation host structures for the positive electrode of electrochemical generators with an alkali metal or silver anode have been essentially crystalline (transition metal didialcogenides and oxides). Yet the discovery of the semiconducting properties of phosphorus pentoxide-based glasses, a quarter of a century ago [1], associated with the synthesis of phosphate-based glasses with high ionic conductivity [2, 3] allows us to consider the possibility of employing glasses as positive electrode materials. These materials could offer significant technological advantages due to their vitreous structure: 1. Easy to synthesize; 2. Easy to implement, in particular in the form of micronic powders; 3. Isotropic structure, implying a larger electrochemically active surface than in the case of low dimensionality crystalline structures; 4. The good conductivities observed in glasses suggest a high diffusion coefficient of the mobile ion; 5. The low density of glasses infers a large number of available sites for the intercalants and, consequently, independence of the volume of the material with respect to the intercalation ratio. The use of glasses for the positive electrode of solid state secondary batteries should ensure that good contacts are maintained throughout the discharge-charge cycles; 6. The use of the same forming oxide in the electrolyte and the electrode should avoid a clear-cut localization of their interface since the macromolecular chains of the forming oxide will extend without interruption from the electrolyte to the electrode.

Materials for electrolyte: Fast-ion-conducting glasses

Apart from crystalline materials, the second class of solid electrolytes is the family of amorphous conductors which in contrast more closely resemble liquid electrolytes than crystalline solids. It is easier to define an amorphous state by saying what it is not than by precisely specifying what it is. Amorphous materials are noncrystalline substances. They lack long-range periodic ordering of their constituent atoms. That is not to say that amorphous materials are completely disordered on the atomic scale. Local chemistry provides almost rigorous bond-length, and to a lesser extent, bond-angle constraints on the nearest-neighbor environment. For instance, unlike amorphous metals, amorphous semiconductors do not consist of close-packed atoms, but rather they contain covalently bonded atoms arranged in an open network with correlations in ordering up to the third- or fourth-nearest neighbors. The short-range order is directly responsible for observable semiconductor properties such as optical absorption edges and activated electrical conductivities.

Materials for electrolyte: Thin-films

The purpose of this chapter is to introduce the area of solid-electrolyte thin-films and to discuss the various process/property/applications relationships which have been developed in this field. Thin-film technology is examined from the interrelated viewpoints of product application, materials structure/properties relationships, and manufacturing-deposition methods. Special emphasis is given to the thin-film materials properties of lithium-borate glasses, which are likely to have an impact on electrochemical device performance, coupled with the various techniques employed to control those properties.

Materials for Electrodes: Crystalline Compounds

The purpose of this chapter is to give a general overview of the properties of compounds such as electrode materials in lithium batteries, particularly those in which there is an appreciable amount of ionic transport within solid components.

Materials for electrolyte: Crystalline compounds

Superionic conductors are solid compound materials that present an anomalously high ionic conductivity, comparable, in order of magnitude, to that of liquid electrolytes. They also present effective atomic diffusion coefficients of the same order as in liquids or gases. These phenomena are observed in such a variety of substances including crystals, glasses, and polymers. In general the conductivity increases with temperature T according to the Arrhenius law. Systems with ionic conductivity of order of 1 S cm-1 at room temperature are ideal for practical applications but many useful materials show results which are several orders of magnitude lower than this. For comparison, the ionic conductivity of the ordinary ionic conductor NaCl is about 10-15 S cm-1 at room temperature. The common structural feature of these materials is the existence of conduction paths connecting fractionally occupied sites.

Design and optimization of solid-state microbatteries

A battery is a device that converts the chemical energy contained in its active materials directly into electrical energy by means of an electrochemical oxidation-reduction reaction, also called redox reaction. This type of reaction involves the transfer of electrons from one material to another through an internal circuit.