(Invited) Improving Calendar Life of Si-Based Lithium-Ion Batteries By FEC/VC-Free Electrolytes

Abstract

Silicon (Si) has been regarded as one of the most promising anode materials for the next generation lithium-ion batteries (LIBs) with high energy density because it has 10 times higher theoretical specific capacity (4200 mAh/g) than that of graphite. However, severe volume change (~300%) of Si during lithiation and delithiation hinders the practical application of Si anode. In the last decade, significant progresses have been made on the specific energy and cycle life of Si based LIBs. However, calendar-life of these batteries is still far less than 10-year target required by DOE’s electrical vehicle (EV) project.In the current work, the role of FEC/VC in conventional carbonate electrolytes has been investigated. It has been found that FEC/VC causes large impedance growth on both Si and graphite anodes at 55 oC. The cut-off voltage of NMC622 has been found to significantly affect its impedance. NMC622 at 4.2V shows no impedance growth at 55 °C for 8 days, while severe impedance growth is observed at 4.4V. To address the instability of both SEI and CEI at elevated temperature, a new Localized High Concentration Electrolyte (LHCE) has been developed to improve the calendar life of Si based LIBs by effectively limiting impedance growth of Si/NMC622 full cells. In addition, the cycle life of the full cell is improved. The mechanism of Si full cells with improved calendar life will also be discussed.