Mild and controllable solid electrolyte interphase formation for high-voltage lithium metal batteries in a wide-temperature range from −40 °C to 80 °C

Wide-temperature and high-voltage lithium metal batteries (LMBs) have great potential in electric vehicles, but their applications face major challenges due to unstable interfacial layers. Here, a dual-salt (lithium bis(trifluoromethanesulfonyl) and lithium difluoro(oxalato)borate) ether-based localized high-concentration electrolyte (LHCE) is designed to facilitate the formation of salt-derived interfacial layers. It is proved that the presence of diluent makes the formation of solid electrolyte interphase (SEI) mild and controllable, thereby avoiding the overproduction of reduction product and improving the reversibility of lithium metal anode. Therefore, the electrolyte achieves a high average Coulombic efficiency (CE) of 99.5 % for Li||Cu cell and stable cycling of 4.5 V Li||LiNi0.5Co0.2Mn0.3O2 (NCM523) cell. Benefiting from the excellent compatibility of electrolyte with electrodes, the Li||NCM523 full-cell provides excellent cycling stability under severe conditions (4.5 V, negative/positive capacity ratio ≈ 0.9). Furthermore, the electrolyte exhibits excellent wide-temperature electrochemical performance, enabling the cells to provide 71 % of room-temperature capacity at −40 °C and retain 85 % capacity retention after 200 cycles with high CE at 80 °C. This study shares a new insight into the role of diluent and provides a promising strategy for electrolyte design of wide-temperature and high-voltage LMBs.