(Invited) Rational Design of Localized High Concentration Electrolytes to Enable Long-Term Cycling of Si Anodes

Abstract

To improve the energy density of conventional lithium ion batteries (LIBs), Si anode has been extensively investigated as a high-capacity alternative for carbonaceous anodes. However, large (~300%) volume change of Si anode during cycling and its continuous side reactions with electrolyte significantly limit the application of Si anodes. Herein, we have designed a localized high concentration electrolyte (LHCE) using a novel diluent with desired molecule structure. This electrolyte exhibits an optimized ion solvation structure and enabled largely improved cycling stability of Si anodes at both room and elevated temperatures. The full cells with Si/graphite composite anodes and LiNi0.5Mn0.3Co0.2O2 cathode have demonstrated 80% of capacity retention after 500 cycles in 1.74M LiFSI in DMC with 1H,1H,5H-Octafluoropentyl 1,1,2,2-tetrafluoroethyl ether (OTE) (0.51:0.84:0.84) at room temperature. The similar cells can also retain 76.5% of capacity in 300 cycles at 45 oC, which is 26% higher than that obtained in the baseline electrolyte. The Si/graphite anode cycled in the new electrolyte exhibits considerably suppressed SEI growth and well preserved dense structure. The design principle for LHCE developed in this work provides an important guideline for future design of practical electrolyte to realize long cycle life of Si anode and other high-capacity alloy materials with large volume changes.