Lithium battery electrolyte decay principle decomposition

If the lithium battery electrolyte does not have side reactions, the lithium battery can theoretically achieve unlimited cycles. However, since conventional carbonate-based electrolytes are not stable on the surface of the positive and negative electrodes, the electrolyte will undergo analytical reactions on the surfaces of the positive and negative electrodes during use, resulting in continued decline in battery capacity. There are many studies on the analysis reaction of electrolyte decay on the surface of the positive and negative electrodes, but most of the experiments are carried out under laboratory conditions. The repeated charging and discharging of the battery in a fixed cycle system causes the decay of the battery. In turn, the degradation mechanism of the battery is decomposed. However, in actual use, the working conditions of lithium batteries are much more complicated. For example, short-term rapid acceleration, rapid charging, long-term storage, etc. are important reasons for electrolyte analysis. The attenuation of the electrolyte contains solvent components such as DMC and EMC. These two solvents will undergo transesterification during use and generate DEC with a similar structure. This is the reason why we find a small amount of DEC in most electrolytes (0.3 -1.3%). In lithium batteries, in addition to the analysis reaction of the solvent, the LiPF6 in the electrolyte also undergoes the analysis reaction. Generally, we think that the analysis of lithium salt is mainly due to the trace moisture in the electrolyte. Generally speaking, the moisture content in the electrolyte of commercial lithium batteries is less than 20mg/L, but the moisture content of batteries disassembled from electric vehicles is much higher than this value (995, 643, 113 and 290mgL-1). LiPF6 analyzes the product POF3 appearing under the application of water. Due to the relatively high reaction activity, only part of the electrolyte is present in the presence of POF3, but the POF3 in the electrolyte will be further analyzed into the product DFP. Although DFP is an analysis product of LiPF6, in fact DFP can help form a more stable SEI film, thereby improving the cycle performance of the battery. A small amount of HF was also formed during the analysis of LiPF6, and HF eventually formed LiF on the negative electrode, which became a part of the SEI film. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: How to repair and maintain lead-acid batteries?