Chitosan-<i>grafted</i>-poly(aniline-<i>co</i>-anthranilic acid) as a water soluble binder to form 3D structures for Si anodes

Abstract

We graft an electrically conductive poly(aniline-<i>co</i>-anthranilic acid) (PAAA) polymer capable of interacting with Si particles onto chitosan, a natural hydrophilic polymer, to form a chitosan-<i>grafted</i>-PAAA (CS-<i>g</i>-PAAA) copolymer, and use it as a new water soluble polymeric binder for Si anodes to relieve the physical stress resulting from Si volume change during charge/discharge cycles. The carboxylic acid functional groups within the PAAA structure, as well as the chitosan functional groups, bind to silicon particles to form a stable 3D network, resulting in high adhesion. Because the binder is conductive, the electrode using the CS-<i>g</i>-PAAA-8 : 1 with an optimal composition ratio of CS to PAAA of 8 : 1 shows a high initial capacity of 2785.6 mA h g^-1, and maintains a high capacity of 1301.0 mA h g^-1 after 300 cycles. We also extract chitosan directly from crab shells, and fabricate a Si@ECS-<i>g</i>-PAAA electrode by grafting PAAA onto the extracted-chitosan (ECS). This electrode records an initial capacity of 3057.3 mA h g^-1, and maintains a high capacity of 1408.8 mA h g^-1 with 51.4% retention after 300 cycles. Overall, we develop a polymeric binder with outstanding cell properties, ease of fabrication, and high water solubility for Si anodes by grafting a conductive PAAA onto chitosan.