Tailoring the interface of lithium metal batteries with an in situ formed gel polymer electrolyte

Abstract

Owing to the high reaction activity of lithium metal, liquid electrolytes (LEs) are unable to meet the demands for high energy density lithium metal batteries (LMBs). In situ formation of a gel polymer electrolyte (GPE) in LMBs is an effective way to tailor the interface of electrodes in LMBs. Herein, a new way to form a GPE has been proposed by heating the precursor LE-containing polymer with hydroxyl and nitrile groups. A crosslinking reaction between the functional groups is initiated by the decomposition product of LiPF₆ without the need of an extra initiator. The polymer chains are covalently crosslinked by amide groups through the Ritter reaction. The in situ formed GPE has a wide electrochemical stability window (>4.89 V), high ionic conductivity (1.20 mS cm⁻¹) and high Li⁺ transference number (0.65). The cycling performances of the Li‖Li symmetric batteries was clearly improved with the in situ formed GPE. Scanning electron microscopy images of the Li electrode showed that the GPE can promote uniform Li deposition with a large grain size. X-ray photoelectron spectroscopy analysis and density functional theory calculation confirm that the GPE can contribute to forming a solid electrolyte interface film rich in Li₃N and LiF, which can facilitate homogenizing Li⁺ flux and uniform Li stripping/plating. The in situ formed GPE can be used for various types of LEs, showcasing superior performance in Li‖LiNi_0.6Co_0.2Mn_0.2O₂ and Li‖O₂ batteries. Our study has opened up a new way for the design of GPEs and will certainly promote the development of high energy density LMBs.