Ultra-high voltage solid-state Li metal batteries enabled by in-situ construction of cathode electrolyte interphase through synergistic dual-anion decomposition

Due to their high operating voltages, energy densities and safety performance, all solid-state Li metal batteries (ASSLMB) share a bright application prospect. However, the poor ion transport and contact issue at cathode electrolyte interphase (CEI) will easily lead to severe capacity degradation at high operating voltages, which remained as the bottleneck problem for ASSLMB. In this work, a CEI layer consisting of LiF and LixBOyFz was in-situly constructed through the synergistic decomposition of DFOB− and TFSI− from ionic liquids. At high operating voltages, this stable and thin CEI layer could not only protect the ionic liquid-based electrolytes by suppressing the polarizations and side reactions on the cathodic surfaces, but also facilitate the transfer of interfacial lithium ions. When tested at 0.1C and 60 °C with a high cut-off voltage of 4.5 V, this ASSLMB possessed an initial specific capacity of 190.7 mA h g − 1 and an 80% capacity retention after 100 cycles. Our findings provide a promising approach to realize ionic liquid-based electrolytes in high-voltage ASSLMBs.