Extending Calendar Life of Si-Based Lithium-Ion Batteries by a Localized High Concentration Electrolyte
Ju‐Myung Kim, Ran Yi, Xia Cao, Yaobin Xu, Mark Engelhard, Shalini Tripathi, Chongmin Wang, Ji‐Guang Zhang
Abstract
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||LiNi 0.6 Mn 0.2 Co 0.2 O 2 (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.