Tailored PVDF Graft Copolymers via ATRP as High-Performance NCM811 Cathode Binders

High-nickel layered oxides, e.g., LiNi0.8Co0.1-Mn-0.1-O-2 (NCM811), are promising candidates for cathode materials in high-energy-density lithium-ion batteries (LIBs). Complementing the notable developments of modification of active materials, this study focused on the polymer binder materials, and a new synthetic route was developed to engineer PVDF binders by covalently grafting copolymers from poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) with multiple functionalities using atom transfer radical polymerization (ATRP). The grafted random copolymer binder provided excellent flexibility (319% elongation), adhesion strength (50 times higher than PVDF), transition metal chelation capability, and efficient ionic conductivity pathways. The NCM811 half-cells using the designed binders exhibited a remarkable rate capability of 143.4 mA h g(-1) at 4C and cycling stability with 70.1% capacity retention after 230 cycles at 0.5 C, which is much higher than the 52.3% capacity retention of nonmodified PVDF. The well-retained structure of NCM811 with the designed binder was systematically studied and confirmed by post-mortem analysis.

Automated summary

In this study, a new synthetic route was developed to engineer PVDF binders for high-nickel layered oxides, leading to improved flexibility, adhesion strength, ionic conductivity, and transition metal chelation capability. The NCM811 half-cells using the designed binders showed excellent cycling stability and rate capability, outperforming nonmodified PVDF.