Unlocking 4.9 V Quasi-Solid-State Lithium Metal Battery via Solvent Screening and Interfacial Manipulation.

Parlous structure integrity of the cathode and erratic interfacial microdynamics under high potential take responsibility for the degradation of solid-state lithium metal batteries (LMBs). Here, high-voltage LMBs have been operated by modulating the polymer electrolyte intrinsic structure through an intermediate dielectric constant solvent and further inducing the gradient solid-state electrolyte interphase. Benefiting from the chemical adsorption between trimethyl phosphate (TMP) and the cathode, the gradient interphase rich in LiPFO and LiF is induced, thereby ensuring the structural integrity and interface compatibility of the commercial LiNiCoMnO (NCM811) cathode even at the 4.9 V cutoff voltage. Eventually, the specific capacity of NCM811|Li full cell based on TMP-modulated polymer electrolyte increased by 27.7% from 4.5 to 4.9 V. Such a universal screening method of electrolyte solvents and its derived electrode interfacial manipulation strategy opens fresh avenues for quasi-solid-state LMBs with high specific energy.