Electrolyte Solvation Engineering toward High-Rate and Low-Temperature Silicon-Based Batteries

Silicon (Si)-based batteries can only work in a narrow temperature range, where their subzero operation has been severely hampered by the sluggish charge transfer and ion diffusion processes. In overcoming such kinetic barriers, a weakly solvating electrolyte is tailored herein, which bypasses the Li+ desolvation difficulties by its fluorinated structure that lowers the Li+ solvating capability. Specifically, our recipe is based on 1 M LiFSI in fluoroethylene carbonate (FEC)/bis(2,2,2-trifluoroethyl) carbonate (BTFC) solvents. Additional incorporation of poor-solvating ethyl trifluoroacetate (ETFA) cosolvent further weakens the electrolyte solvation power, while efficaciously lowering the electrolyte viscosity and melting point. Such a combination affords prolonged Si cyclability for 200 cycles at RT (capacity-decay rate of 0.0945% per cycle). Even at −20 °C, the Si electrode still delivers a discharge capacity as high as 2005.7 mAh g–1 that proceeds for 200 cycles. Pairing with a commercial LiNi0.5Co0.2Mn0.3O2 cathode, the full cell affords a capacity of 104.6 mAh g–1 when being charged/discharged at −20 °C, which presented quite stable performance over 100 cycles.