The conventional non-aqueous electrolyte based on 1 mol·dm^-3 LiPF₆/EC has been used for two decades in Li-ion batteries. With the rapid development of higher energy and power densities Li-ion batteries and Lithium batteries (such as Li-O₂, Li-S,etc.), the electrolyte, as an indispensable component in rechargeable batteries, comes to the stage of innovation. Considerable efforts have been made on the research of several new types of electrolytes such as ionic liquid, polymer electrolytes and inorganic solid electrolytes. However, their commercial applications are hampered due to their intrinsic problems. Therefore, researchers begin to revisit the non-aqueous solution, and pay more attention on the concentrated electrolyte. This review summarizes the research on concentrated electrolytes including the development history, the solution structure, the classification criteria, the physicochemical property and the compatibility with electrode, the specific transport properties of lithium ions in the bulk solutions and the interface of electrolyte/electrode, as well as the compatibility of electrolyte and electrode. Besides, the main problems of concentrated electrolyte such as high viscosity and low ionic conductivity are briefly summarized, and the corresponding improvement measures are proposed. Finally, we highlight the research direction of concentrated electrolyte in the future, and provide an idea for the design of new type electrolyte.
Contents
1 Introduction
2 The development of concentrated electrolyte
3 Structural characteristics of concentrated electrolyte
3.1 The effect of lithium salt concentration on the structure of concentrated electrolyte
3.2 The effect of solvent on the structure of concentrated electrolyte
3.3 The effect of anions on the structure of concentrated electrolyte
4 The classification of concentrated electrolyte
5 Physical chemistry and interface properties of concentrated electrolyte
5.1 Thermal stability
5.2 Electrochemical stability
5.3 Ionic transfer property
5.4 Compatibility with electrode materials
6 The disadvantage of concentrated electrolyte
7 Conclusion