Tough Polymer Electrolyte with an Intrinsically Stabilized Interface with Li Metal for All-Solid-State Lithium-Ion Batteries

Abstract

A high-performance solid polymer electrolyte (SPE) membrane that simultaneously addresses the issues of enhanced toughness and Li-dendrite mitigation for all-solid-state Li-ion batteries (ASSLIBs) is demonstrated. The membrane has a sandwiched structure consisting of a center poly(ethylene oxide)/lithium bis(trifluoromethanesulfonyl) imide (PEO/LiTFSI) electrolyte matrix laminated on both sides with electrospun high-polarity β-phase poly(vinylidene fluoride-co-hexafluoropropylene) (β-PVDF-HFP) nanofibers. The nanofiber layers impart remarkable enhancement in both mechanical and electrochemical properties of the SPE, including a 20-fold increase in tensile strength and a 48-fold increase in toughness, along with up to 4-fold enhancement in Li-ionic conductivity. Moreover, the highly polar fluorinated nanofiber cladding layers enable a stable Li-plating/stripping interface on the Li anode to efficiently mitigate dendrite formation, while improving the electrochemical interfacial stability with the cathode. In a Li|SPE|Li symmetric cell, the use of the sandwiched SPE is demonstrated to improve the cycle stability from short-circuiting at 144 h for a pristine PEO/LiTFSI membrane to no short-circuiting even up to 3600 h (1800 Li-plating-stripping cycles). In an example of LiFePO4|SPE|Li ASSLIBs, using the sandwiched membrane enables substantial reduction irreversible capacity upon charging to the high-voltage end and more than 80% capacity retention for over 1600 h. This work presents a feasible and facile design for an SPE for high-performance ASSLIBs.