The electrolyte is an ionic conductor that conducts electricity in the battery and is an important factor affecting the power characteristics of the battery. The organic solvent is the main component of the non-aqueous liquid electrolyte and is closely related to the performance of the electrolyte. Organic solvents with excellent performance are an important guarantee for realizing low internal resistance, long life and high safety of secondary batteries. The main factors to consider when choosing organic solvents are: (1) the influence of organic solvents on battery safety; (2) the redox stability of organic solvents; (3) the compatibility of organic solvents with electrodes; (4) the influence of organic solvent on the conductivity of electrolyte. Common organic solvents for batteries include ethers, carboxylates, carbonates, amines, sulfur-containing, boron-based, etc.
Figure 1. Some organic solvents for batteries
- Improve secondary battery safety: The safety of the battery is related to the flash point, volatility, toxicity of the organic solvent and the reaction of the battery under the abuse state. Batteries may burn or even explode under abuse conditions such as overheating and short circuit. Therefore, the choice of organic solvent should be as high flash point solvent as possible. In addition, the flash point of decomposition products of salt compounds in organic solvents and electrolytes also needs to be considered. In organic solvents, organic compounds with relatively large molecular weights have higher flash points, which can improve the safety of batteries.
- Improve the stability of secondary battery: The increase of battery voltage requires electrolytes with high oxidative stability. The oxidative stability of organic solvents affects the oxidative stability of electrolytes. In order to improve the stability of the electrolyte, certain electronegative groups, such as cyano groups, carbonate groups or ester groups, are often introduced into organic molecules. The introduction of these groups makes the organic solvent have strong oxidation stability and can operate stably at higher voltages.
- Enhanced the conductivity of secondary battery: The dielectric constant and viscosity of organic solvents are important factors affecting the conductivity of electrolytes. The greater the conductivity of the electrolyte, the higher the rated rate of the electrode, which is more conducive to the conduction of electrons. In general, the higher the dielectric constant of the organic solvent, the easier it is for the salts to dissolve and dissociate. Therefore, organic solvents with larger dielectric constant and smaller viscosity are often used as electrolyte components of secondary batteries to obtain higher conductivity.
- Shuang Xia, Xiao-Min Zhang, Kuan Huang, Yong-Le Chen, You-Ting Wu. Ionic liquid electrolytes for aluminium secondary battery: Influence of organic solvents [J]. J. Electroanal. Chem., 2015, 757(15), 167-175.