Electrochemical and mechanical characterization of thermosets as fluorine-free cathode binders for Li-ion batteries

Abstract

This study demonstrates fluorine-free cross-linked (meth)acrylate polymers as alternatives to polyvinylidene fluoride (PVDF) in LiNi_0.33Mn_0.33Co_0.33O₂ (NMC111) cathodes. We determine the effects of thermal initiator content, polymer content, and curing environment for two polymer chemistries: a flexible acrylate polymer, and a stiff methacrylate polymer. Electrodes are manufactured and tested for final electrochemical performance and mechanical properties. The results show that the flexible acrylate polymer exhibits higher rate capability compared to the stiff methacrylate polymer because calendering fractures the brittle network of stiff polymer. Electrode adhesion to the current collector and cohesion between particles are found to be a strong function of thermal initiator ratio and oxygen inhibition. Furthermore, there exists an optimal binder concentration that maximizes rate capability performance. Under the right conditions, the two polymers exhibit comparable performance to PVDF electrodes. These results provide important implications for designing cross-linked polymers as cathode binder alternatives to PVDF.