Multifunctional Fluoroethylene Carbonate for Improving High-Temperature Performance of LiNi_0.8Mn_0.1Co_0.1O₂||SiO_x@Graphite Lithium-Ion Batteries

LiNi0.8Mn0.1Co0.1O2||SiOx@graphite has received great attention in both academia and industry because it has the highest energy density among state-of-the-art commercial lithium-ion batteries. However, it suffers from severe capacity decay during high-temperature cycling or storage, which still needs to be addressed for its commercialization. In this work, fluoroethylene carbonate (FEC) is employed as an additive or a cosolvent to improve the high-temperature performance of 1 Ah LiNi0.8Mn0.1Co0.1O2||SiOx@graphite pouch cells. By adding 5% FEC as additive, the capacity retention increases from 54.5% to 67.0% after 100 cycles at 45 °C. The use of FEC as a cosolvent further increases the capacity retention to 83.3%. The improvement is ascribed to the multifunctional effects from FEC, preventing electrolyte decomposition, mitigating the resistance increment and Mn ions dissolution with the formation of the interface films, which consist of LiF and LiPOxFy species. Therefore, the employment of FEC is of great importance for the development of high-energy-density lithium-ion batteries.