Chitosan based binder for silicon anode and sulphur cathode used in lithium batteries

Abstract

In recent years Lithium-ion batteries have become the choice of secondary battery but to meet current demand of high capacity batteries one has to look beyond the commonly used Carbon-based anodes. Active materials like Silicon have high charge capacity but have high volumetric expansion on lithiation, which often results in low rate capability and limited cycle life. Binders play an important role in the cycling stability of the batteries by keeping the particles in electrical contact, providing best elasticity to the anode composite and accommodate the volume expansion of Silicon during cycling. It has been found that using different biopolymers like cellulose, carboxymethyl cellulose (CMC), sodium alginate, etc. as binders can give a better cycling stability than Polyvinylidene fluoride (PVDF). This research focuses on using Chitosan, the second most abundant biopolymer found in nature, as a binder for Silicon anodes and Sulphur cathodes. Chitosan and its derivative Chitosan-tripolyphosphate (TPP) obtained by ionic crosslinking with polycations were used as binders for Si anodes, providing a capacity retention of 73% and 64% after 100 and 500 cycles, respectively at 0.1C. Carbon nanofibers (CNF) and freeze drying of anode improved discharge capacity and cycling stability, increasing the capacity retention to 86% and 96%, respectively, after 500 cycles at 0.1C. Chitosan and ChitosanTPP were used as binders along with CNF for Sulfur cathodes, providing excellent cycling performance through effective trapping of the polysulfides formed and mitigating the volume expansion during cycling, having a capacity retention of about 82% and 90% after 200 cycles at 0.1C, respectively. Highly conductive polymers such as Polypyrrole and Poly(3,4-ethylenedioxythiophene) (PEDOT) were added to synthesize a crosslinked conductive binder which improved the performance of the Si and S electrodes by providing high conductivity to the active materials throughout cycling and increased the capacity because of addition of more active materials.