Surface Modification of Ga-Doped-LLZO (Li₇La₃Zr₂O₁₂) by the Addition of Polyacrylonitrile for the Electrochemical Stability of Composite Solid Electrolytes

Abstract

Composite solid electrolytes (CSEs), often incorporating succinonitrile (SCN), offer promi I confirm sing solutions for improving the performance of all-solid-state batteries. These electrolytes are typically made of ceramics such as Li7La3Zr2O12 (LLZO) and polymers such as poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP). Garnet-applied polymer–ceramic electrolyte (g-PCE) is composed of PVDF-HFP, SCN, and LLZO. However, the interface between SCN and LLZO is reportedly unstable owing to the polymerization of SCN. This polymerization could cause two serious problems: (1) gelation during the mixing of LLZO and SCN and (2) degradation of ionic performance during charge and discharge. To prevent this catalytic reaction, polyacrylonitrile (PAN) can be added to the g-PCE (g-PPCE). PAN blocks the polymerization of SCN through a cyclization process involving La ions which occurs more rapidly than SCN polymerization. In this study, the enhanced chemical stability of the garnet-applied PAN-added polymer ceramic electrolyte (g-PPCE) was achieved by using an impregnation process which added SCN with 5 wt.% of PAN. The resulting CSE has an ionic conductivity of ~10-⁴ S/cm at room temperature. Coin-type cells assembled with LFP (LiFePO4) and LNCM (LiNi0.6Co0.2Mn0.2O2) cathodes with Li-metal anodes show specific discharge capacities of 150 and 167 mAh/g at 0.1 C, respectively, and stable cycle performance. Additionally, a pouch-type cell with a discharge capacity of 5 mAh also exhibits potential electrochemical performance.

Keywords

• composite solid electrolyte
• garnet oxide
• polymerization
• cyclization
• solid-state Li-metal battery