Enhancing NCM811 Cathode Performance via Curing Temperature Optimization of Fluorine-free Polyimide Binders with Carbon Nanotubes

In lithium-ion batteries, high-nickel LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes have attracted considerable attention owing to their high energy density. Although conventional poly(vinylidene fluoride) (PVDF) has generally been used as the standard binder, the fluorine (F) in its chemical structure poses severe environmental concerns, driving a global shift toward sustainable, F-free alternatives. This study introduces poly(amic acid) (PAA), which is thermally converted into a rigid polyimide (PI) binder, in NCM811 and multi-walled carbon nanotubes (MWCNTs) conductive network. The degree of imidization was controlled by varying the curing temperature and optimized using FTIR spectroscopy. The optimized PAA 250 electrode exhibited a comparable capacity retention to that of the conventional PVDF electrode after 100 cycles. Furthermore, cross-sectional SEM and XPS after cycling revealed that the PAA binder suppresses particle microcracking and transition metal dissolution. This robust passivation is further supported by ex-situ FTIR and XRD analyses. Consequently, these findings demonstrate that the structural and chemical stability of the imidized PAA binder makes it a promising fluorine-free alternative for high-performance and environmentally sustainable battery systems.