In the current known development and application of low temperature batteries, low temperature lithium iron phosphate batteries are basically the same in terms of electrode materials, separators, pole pieces, and tab housings, and they are similar in terms of improving low temperature performance. The difference is the low temperature electrolyte, which is relatively large and directly affects the discharge performance of the battery in a low temperature environment. Therefore, an important source of improving the performance of low temperature lithium iron phosphate batteries starts from the electrolyte.
The operating temperature range of a lithium ion battery shows its application characteristics. At very low temperatures, aerospace requires lithium ion batteries to have a reasonable discharge efficiency from -60°C to -80°C, while the drilling industry requires good performance at temperatures above 100°C.Except for these two market segments, the temperature window for most lithium ion battery applications is -50C to 80C. These windows include household electronics and power tools (-20°C to 60°C), HEV (-30°C to 70°C) and military applications (-50°C to 80°C).
1.Flux for lithium ion battery electrolyte
At present, the solvents of lithium ion battery electrolytes mostly use carbonate series of high-purity organic solvents, such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and so on. However, the performance of a single solvent is often not able to have the various performances that are actually required at the same time. The multi-component mixed solvent obtained by mixing multiple solvents in a certain ratio is often better than a single solvent. To improve the low temperature performance of the electrolyte by optimizing the organic solvent is to find a low-melting organic solvent that is miscible with the current electrolyte.
Use the electrolyte solvent system with good conductivity at low temperature to increase the body temperature of the battery during charging and discharging at low temperature, such as choosing the solvent system DMC+MA.
Use organic solvents with lower melting point and viscosity to broaden the liquid temperature range of the electrolyte, such as using carboxylic acid ester solvents such as ethyl propionate and methyl butyrate.
2.The development of lithium ion battery
At present, the most widely used lithium salt is LiPF6. The important reason is that it has good solubility in organic solvents, relatively high conductivity, and relatively low cost.
However, because LiPF6 is very sensitive to trace amounts of water, its decomposition products contain HF, which is easy to corrode cathode materials and current collectors, and its lack of temperature stability affects the development of lithium ion batteries. It is also one of the important ways to improve the low temperature performance of the electrolyte by using a more stable lithium salt with better low temperature performance.
Adding additives to improve the low temperature performance of organic electrolytes for lithium ion batteries is another research focus and an important development direction in this field in the future. Additives have the characteristics of small dosage and quick effect, which can significantly improve the performance of lithium ion batteries without basically increasing the production cost and changing the production process.