Ionic-conductive poly (vinylidene fluoride) polymer as a versatile binder to stabilize high-voltage LiCoO2 cathode materials

Abstract

Serious structural irreversibility and interfacial side reactions pose major challenges for the stable operation of LiCoO₂ cathodes at high voltages. Herein, we report a polymer-based solid electrolyte (SLP) composed succinonitrile, LiTFSI and PVDF as a binder to address these issues. The SLP binder exhibits superior performance compared to traditional PVDF and PVDF binders with LiTFSI, with higher ionic conductivity (8.46 × 10^− 5 S cm^− 1 at 30 ℃), lower activation energy of 0.38 eV and excellent adhesion. Even with just 3% SLP binder, LiCoO₂ cathode operating at a cutoff voltage of 4.6 V and loaded with ~ 6.0 mg cm^− 2 active material demonstrates improved rate capability at higher compaction densities, delivering a discharge specific capacity of 146.5 mAh g^− 1 after 100 cycles at 0.5 C-rate. The SLP binder not only enhances Li⁺ conduction but also facilitates the formation of a stable cathode-electrolyte interphase, thus reducing the Li⁺ diffusion barrier and interface polarization, and enhancing battery’s performance at low temperature. Furthermore, the SPL binder’s high compatibility and elasticity with the electrolyte mitigate irreversible structural changes and volume expansion in LiCoO₂ during cycling, leading to better preservation of the layered structure and lower internal stress for stable cycling under high temperatures. This strategy provides a novel interface protection idea for electroceramic cathode materials and may facilitate commercial development.