Extending Calendar Life of Si-Based Lithium-Ion Batteries by a Localized High Concentration Electrolyte

Although significant progress has been made on the cycle life of silicon (Si)-based lithium (Li)-ion batteries (LIBs), their calendar life is still far less than those required for electrical vehicle applications. Here, the fundamental mechanisms behind the limited calendar life of Si-LIBs were systematically investigated. It is found that fluoroethylene carbonate (FEC) additive typically used in the electrolyte to enhance the room temperature cycling stability of Si-LIBs is responsible for the rapid impedance increase of Si-LIBs during storage at 55 °C. An FEC-free localized high-concentration electrolyte (lithium bis(fluorosulfonyl)imide:ethyl propionate:ethylene carbonate:1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (1:2.8:0.2:1 by mol.) with 1 wt % lithium difluorophosphate) promotes stable interphase layers formed on electrodes that can effectively block the crosstalk between cathode and anode and minimize the impedance increase of Si||LiNi0.6Mn0.2Co0.2O2(NMC622) batteries during storage at 55 °C, therefore largely improving their calendar life. Si||NMC622 batteries using this electrolyte demonstrated a high-capacity retention of 92.4% after 500 cycles at 45 °C with a well-preserved electrode structure. The failure mechanism revealed in this work and the approach used to improve the stability of Si-LIBs can also be used to improve the calendar life of other rechargeable batteries.