Liquid electrolyte confined in polymer crystals: A novel strategy for quasi-solid-state lithium‑oxygen batteries

Abstract

Lithium‑oxygen batteries (LOBs) have very high theoretical energy density, but the cycle performance is not satisfactory due to numerous obstacles such as the poor interfacial stability of liquid electrolyte (LE) on both cathode and Li metal anode, the leakage of liquid electrolyte, the cross-over of oxygen and moisture, etc. Quasi-solid-state polymer electrolytes are feasible choices to deal with the problems associated with LE and Li anode. Here, a novel strategy is used to prepare quasi-solid-state polymer electrolytes by confining LE in polymer crystals. The trioxymethylene is polymerized in LE, and the as formed polyoxymethylene (POM) crystallizes with the formation of lamellar crystals of hierarchical micro/nano architectures, which confine the liquid exponents in LE and become quasi-solid-state POM electrolytes (POMEs). The POME-30 has high ionic conductivity, wide electrochemical stability window and high Li⁺ transference number. Molecular dynamics simulation shows that there exist channels for Li⁺ to migrate faster on the interface of POM lamellar crystals. POME-30 has excellent interfacial compatibility with Li anode, and can promote more uniform Li deposition and stripping. The in situ formed quasi-solid-state Li|POME-30|O₂ batteries can be cycled for 143 cycles in O₂ and 67 cycles in ambient air. XPS analysis results suggest that the cross-over of H₂O and CO₂ can be greatly suppressed. Moreover, the quasi-solid-state Li|POME-30|air pouch battery can be stably cycled for over 30 cycles, showing great safety performance even folded or cut. Our strategy of in situ integrating rigid lamellar crystals in LE has paved a new way for exploring advanced polymer electrolyte, which is sure to promote the development of high energy-density lithium metal batteries.