Intimate interaction of TFSI− anions with MoO3−x oxygen vacancies boost ionic conductivity of cathode-supported solid polymer electrolyte

Abstract

A solid-state electrolyte should display high ionic conductivity, low interfacial impedance, good mechanical properties, and stability. Although poly(ethylene oxide) (PEO) has been investigated extensively as a potential polymer host in solid polymer electrolytes (SPEs), it suffers from low ionic conductivity, flammability, Li dendrite growth, and poor mechanical strength. In this study, we developed a composite cathode-supported SPE featuring oxygen-deficient MoO3–xnanobelts (MNBs) as passive nanofillers to address these issues. The synthesis of MNB is easy, economical, and scalable, enabling large-scale production of SPE. Relative to the PEO-only SPE, the composite SPE with 5 % MNBs (PMNBs-SPE) exhibited greater ionic conductivity (4.28 × 10–4S cm−1) at 60 °C, enhanced mechanical strength, superior cycling performance, and lower flammability. The greater ionic conductivity resulted from the dissociation of LiTFSI in the presence of oxygen vacancies acting as Lewis acid sites and the shorter diffusion pathways induced by the MNBs. In addition to density functional theory (DFT), for the first time we acquiredthe time-of-flight secondary ion mass spectrometry (ToF-SIMS)to reveal the occurrence of LiTFSI dissociation. Our study is the first to assess how nanofillers influence the generation of gaseous products in solid polymer batteries by using online gas chromatography and mass spectrometry. The as-fabricated cathode-supported SPE with LiFePO4(LFP)||PMNBs-SPE||Li cell delivered a discharge capacity of approximately 145 mA h g−1for 50 cycles; the SEG||PMNBs-SPE||Li cell exhibited an initial discharge capacity of approximately 648 mA h g−1measured at a rate of 0.1C at 60 °C.