Salt-with-Salt, a novel strategy to design the flexible solid electrolyte membrane for highly safe lithium metal batteries

Abstract

As one of the outstanding candidates for solid polymer electrolytes (SPEs), poly(vinyl formal) (PVFM) based SPEs are facing higher requirements toward practical application such as further improving ambient ionic conductivity, lithium ion transference number, and suppressing interfacial passivation on the electrode. Based on lithiated PVFM single lithium-ion conductor (LiPVFM), a novel Salt-with-Salt concentrated flexible SPEs membrane have been prepared herein via intermolecular design as Dual-Li SPEs for highly safe solid-state lithium metal batteries. Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) dissolves in LiPVFM matrix to obtain the composite unexpectedly with a decreased glass transition temperature (T_g) and an inherited amorphous structure. Moreover, lithium ions are dissociated by the dominant ether ring groups in LiPVFM, improving the charge concentration of the electrolyte. Therefore, Dual-Li SPEs is achieved with high ionic conductivity of 5.7 × 10⁻⁴ S cm⁻¹ at 25 °C, high lithium ion transference number of 0.79, excellent elasticity and stability on the interface of lithium metal anode. Li/Dual-Li SPEs/LiCoO₂ batteries process a high reversible capacity in 200 cycles, high coulombic efficiency of 99% and high safety in bending and punching test. The work paves a new way for developing solid polymer electrolyte membrane with ideal integrated properties for lithium metal batteries.