High-Voltage Li Metal Batteries Enabled by Adsorption-Defluorination Mechanism

High-voltage lithium metal batteries can theoretically achieve the highest energy density, yet the vulnerable interphases formed between the electrolytes and electrodes pose short battery life and safety issues. Herein, a fluorinated siloxane-based electrolyte (FSOE) compatible with a lithium metal anode and high-voltage cathode simultaneously is designed. Besides the benign solid electrolyte interphase (SEI) at the Li surface, the FSOE induces a thin passivation layer formed on high-voltage lithium cobalt oxide (LCO) via an adsorption–defluorination process. This process enlarges the energy difference between the Co 3d and the O 2p band center at the LCO cathode surface, effectively stabilizing the delithiated LCO. The formulated electrolyte, consisting of 2.2 M LiFSI in (3,3,3-trifluoropropyl)methyldimethoxysilane, endows the 4.5 V 20-μm-Li||2-mAh-cm–2-LCO full cell (N/P ratio = 2) with 95% capacity retention after 450 cycles and enables the Li-free Cu||NMC532 pouch cell over 100 cycles. The adsorption–defluorination mechanism provides a promising approach to stabilize high-voltage cathodes, offering significant potential for practical LMBs.