Electrospun Perovskite Nanofiber/Poly(vinylidene fluoride-cohexafluoropropylene) Quasi-Solid-State for Lithium-Metal Batteries

Abstract

Solid-state lithium-metal batteries (SSLMBs) with a composite solid electrolyte (CSE) have great potential for achieving both high energy density and high safety and are thus promising next-generation energy storage devices. Nevertheless, the key bottleneck issues are a high electrode/electrolyte interface resistance and the limited Li+ conductivity of the solid electrolyte. A free-standing CSE consisting of Li0.33La0.557TiO3 (LLTO) nanofibers, poly(vinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is developed for room-temperature SSLMB applications. First, the calcination temperature for the electrospun LLTO precursor is optimized. The effects of the LLTO filler fraction and the morphology (spherical vs. fibrous) on CSE conductivity are examined. Furthermore, a succinonitrile interlayer (SNI), which is composed of succinonitrile, fluoroethylene carbonate, and LiTFSI, is developed to lower the high interfacial impedance. Compared to a conventional ester-based interlayer (EBI), SNI effectively decreases the Li//CSE interfacial resistance and suppresses unfavorable interfacial side reactions. The derived LiF- and CF x -rich protective layer on the Li electrode surface prevents the accumulation of dead Li and the excessive formation of SEI. Importantly, the dehydrofluorination reactions of PVDF-HFP are adequately mitigated, and a highly conductive and stable Li//CSE interface is achieved owing to SNI. Accordingly, both Li//CSE@SNI//Li and Li//CSE@SNI//LiFePO4 cells exhibit superior charge-discharge properties and cyclability to those of an EBI counterpart. A simple and low-cost interface modification strategy to enhance the performance of SSLMBs is proposed in this paper.