In Situ Construction of Rapid Li⁺ Transport Channels and a Stable LiF-rich SEI via Li₂CO₃ Conversion on Garnet Surfaces for All-Solid-State Batteries

A facile surface modification of LLZO is realized via mild acid-base neutralization with pentafluorobenzoic acid (PFA), which efficiently removes surface Li₂CO₃ without destroying the LLZO crystal structure. • The modified LLZO promotes fast lithium-ion transport at the ceramic/polymer interface and facilitates the formation of a stable LiF-rich solid-electrolyte interphase. • This surface engineering approach significantly improves the interfacial compatibility and long-term cycling stability of PEO-based composite solid electrolytes. Li₇La₃Zr₂O₁₂ (LLZO) and polyethylene oxide (PEO)-based composite solid electrolytes (CSE) demonstrate favorable potential for practical applications. However, the Li₂CO₃ passivation layer tends to form on the surface of LLZO particles, which severely degrades the electrochemical performance of the CSE. Herein, a facile surface modification strategy for LLZO is developed via a mild acid-base neutralization reaction between pentafluorobenzoic acid (PFA) and surface Li₂CO₃ in methanol solvent. With 3 wt% PFA addition, Li₂CO₃ can be efficiently eliminated, accompanied by the in-situ formation of a organic coating layer (3PFA@LLZO). The as-prepared 3PFA@LLZO can be then composited with a PEO matrix to obtain 3PFA@LLZO-PEO composite solid electrolytes. It has been found that the 3PFA@LLZO-PEO exhibits a high ionic conductivity of 1.23 × 10⁻⁴ S/cm at 30 °C. More importantly, the in-situ-formed lithium pentafluorobenzoate promotes the construction of a LiF-rich solid-electrolyte interphase (SEI), which greatly enhances the interfacial stability and compatibility. Consequently, at 30 °C, The LiFePO₄(LFP)/Li half-cell displays a capacity retention of 80% after 400 cycles at 0.5C, while the LiNi 0.7 Co 0.1 Mn 0.2 O 2 (NCM)/Li half-cell presents a high capacity retention of 91.7% after 170 cycles at 0.3C. Therefore, it distinctly demonstrates that the proposed surface modification strategy effectively elevates the comprehensive electrochemical performance of PEO-LLZO composite solid electrolytes. Download: Download high-res image (239KB) Download: Download full-size image