Study on the effect of fluorinated solvent electrolyte on the active material and cycle performance of a commercial 21700-type battery

Different electrolyte schemes were studied on the traditional commercial 21700-type battery. The effect of different fluorinated electrolytes on the cycle performance of the battery was systematically investigated. When methyl (2,2,2-trifluoroetyl) carbonate (FEMC) was introduced, due to the low conductivity of FEMC, the polarization and internal resistance of the battery increased, which leads to the increase of constant voltage charging time, leading to the cracking of the cathode material and reduction of the cycle performance. When ethyl difluoroacetate (DFEA) was introduced, the poor chemical stability caused by its low molecular energy level led to the decomposition of the electrolyte. Thus, affecting the cycle performance of the battery. However, the introduction of fluorinated solvents can form a protective film on the surface of the cathode, which can effectively inhibit the dissolution of metal elements. The fast-charging cycle of commercial batteries is generally set at 10–80% SOC, which can effectively reduce the H2 to H3 phase transformation process, and the temperature rise caused by fast-charging can also reduce the effect of electrolytic conductivity, so that the protective effect of the fluorinated solvent on the cathode material is dominant. Therefore, the fast-charging cycle performance is improved.