Electrolyte Engineering for High-Voltage Lithium Metal Batteries

High-voltage lithium metal batteries (HVLMBs) have been arguably regarded as the most prospective solution to ultrahigh-density energy storage devices beyond the reach of current technologies. Electrolyte, the only component inside the HVLMBs in contact with both aggressive cathode and Li anode, is expected to maintain stable electrode/electrolyte interfaces (EEIs) and facilitate reversible Li⁺ transference. Unfortunately, traditional electrolytes with narrow electrochemical windows fail to compromise the catalysis of high-voltage cathodes and infamous reactivity of the Li metal anode, which serves as a major contributor to detrimental electrochemical performance fading and thus impedes their practical applications. Developing stable electrolytes is vital for the further development of HVLMBs. However, optimization principles, design strategies, and future perspectives for the electrolytes of the HVLMBs have not been summarized in detail. This review first gives a systematical overview of recent progress in the improvement of traditional electrolytes and the design of novel electrolytes for the HVLMBs. Different strategies of conventional electrolyte modification, including high concentration electrolytes and CEI and SEI formation with additives, are covered. Novel electrolytes including fluorinated, ionic-liquid, sulfone, nitrile, and solid-state electrolytes are also outlined. In addition, theoretical studies and advanced characterization methods based on the electrolytes of the HVLMBs are probed to study the internal mechanism for ultrahigh stability at an extreme potential. It also foresees future research directions and perspectives for further development of electrolytes in the HVLMBs.