Highly Elastic Block Copolymer Binders for Silicon Anodes in Lithium-Ion Batteries

Abstract

Silicon (Si) is a promising anode material to replace the broadly adopted graphite due to its high capacity and abundant source. However, Si anodes suffer from severe problems of huge volume change (∼300%), and the commonly used binders like poly(vinylidene fluoride) (PVDF) cannot accommodate such changes. Here, we report a tough block copolymer PVDF-<i>b</i>-Teflon (PTFE) binder that can coalesce pulverized Si and thus enhance the stability of Si anodes. The suspension copolymerization of vinylidene fluoride and tetrafluoroethylene produces elastic PVDF-<i>b</i>-PTFE with large breaking elongations of >250% and high viscosity as well as high ionic conductivity and thermal stability. We show that 5 wt % of the binder forms elastic cobweb structures in the electrode matrix that can effectively coalesce Si particles and conductive agents together, enabling long cycling stability (>250 cycles) and high rate performance (1 C) for electrodes at a commercial-level Si loading of 1 mg·cm^-2. The findings point out to a promising strategy for developing highly elastic and tenacious binders for electrodes with large volume changes during the electrochemical reactions.