Comonomer-Tuned Gel\nElectrolyte Enables Ultralong\nCycle Life of Solid-State Lithium Metal Batteries

Abstract

Rechargeable lithium metal batteries (LMBs) are considered\nthe\n“holy grail” of energy storage systems. Unfortunately,\nuncontrollable dendritic lithium growth inherent in these batteries\nhas prevented their practical applications. The benefits of solid-state\nelectrolyte for LMBs are limited due to the common compromise between\nionic conductivity and mechanical property. This work proposes a mechanism\nfor simultaneous improvement in ionic conductivity and mechanical\nstrength of gel polymer electrolyte (GPE) which is based on tunable\ncross-linked polymer network through adjusting monomer ratios. With\nincreasing bisphenol A ethoxylate dimethacrylate (E2BADMA) and poly(ethylene\nglycol) diacrylate (PEGDA) mass ratios in GPE precursors, the formed\npolymer network experienced a composition evolution from a 3D cross-linked\nmono PEGDA network to triple PEGDA, E2BADMA, and PEGDA/E2BADMA networks\nand then to dual E2BADMA and PEGDA/E2BADMA networks, accompanied by\nthe increase in both storage modulus (from 6 to 37 MPa) and ionic\nconductivity (from 0.06 to 0.44 mS cm^–1). As a result,\nthe E2BADMA/PEGDA mass ratio of 2:1 facilitates the successful fabrication\nof a dual-network-supported GPE (PEEPL-12) with a mechanical strength\nof 37 MPa and superior electrochemical properties (a high ionic conductivity\nof 0.44 mS cm^–1 and a wide electrochemical stability\nwindow of 4.85 V vs Li/Li⁺). Such polymer electrolyte-based\nsymmetric lithium metal batteries delivered a long cycle life (2000\nh at 0.1 mA cm^–2 and 0.1 mAh cm^–2), and the Li|PEEPL-12|LiFePO₄ cell delivered a high capacity\nof 140 mAh g^–1 at the 100th cycle at the current\ndensity of 0.1 C (1 C = 170 mAh g^–1). A more thorough\ninvestigation indicated the formation of a stable solid electrolyte\ninterphase layer on a lithium metal anode. These extraordinary features\nopen up a venue for fabrication of advanced polymer electrolyte for\nlong-cycle-life lithium metal batteries.