Constructing Ion Bridges With Competitive Coordination Effects to Promote Li⁺ Conduction in Solid-State Electrolytes for High-Performance Lithium Metal Batteries.

Abstract

Composite solid electrolytes (CSEs) based on poly(vinylidene fluoride)-co-hexafluoropropylene (PVDF-HFP) and Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO) are considered among the most promising SEs for achieving high-energy-density solid-state batteries. However, low ionic conductivity and poor interfacial compatibility pose significant challenges for their practical applications. Herein, a strategy involving the construction of Li_xTaO_xF_5- _x (LTOF) ion bridges with competitive coordination effects on the LLZTO surface is proposed. This approach alleviates restrictions on Li⁺ transport and enhances Li⁺ transport kinetics. The introduction of LTOF weakens Li⁺ coordination strength, suppresses electron localization at the LLZTO/PVDF-HFP interface, and simultaneously reduces PVDF-HFP crystallinity. This creates multiple efficient Li⁺ transport pathways and an interphase with excellent compatibility. Consequently, the prepared electrolyte exhibits a high ionic conductivity of 1.21 mS cm^- ¹. Attributing to easier lithium salt dissociation, the solid electrolyte interface enriched with inorganic components, e.g. LiF/Li₃N/Li₂S, enables the Li|CSE-9TF|Li cell to maintain stable plating/stripping for over 1100 h at a current density of 0.8 mA cm^- ². The assembled LiFePO₄||Li cells deliver high capacity retention (93.4%) and approaching 100% coulombic efficiency after 1000 cycles at 1C. This work proposes a strategy for regulating the coordination environment and improving interfacial compatibility through surface oxyhalide layers, facilitating new progress in the practical application of CSEs.