Dependency of Electrochemical Performances of Silicon Lithium-Ion Batteries on Glycosidic Linkages of Polysaccharide Binders

Abstract

Molecular structures of polysaccharide binders determining mechanical properties were correlated to electrochemical performances of silicon anodes for lithium-ion batteries. Glycosidic linkages (alpha and beta) and side chains (-COOH and -OH) were selected and proven as the major factors of the molecular structures. Three different single component polysaccharides were compared: pectin for a linkages versus carboxylic methyl cellulose (CMC) for beta-linkages from the linkage's standpoint, and pectin as a COOH-containing polymer and amylose as its non-COOH counterpart from the side chain's standpoint. Pectin was remarkably superior to CMC and amylose in cyclability and rate capability of battery cells based on silicon anodes. The pectin binder allowed volume expansion of silicon electrodes with keeping high porosity during lithiation due to the elastic nature the chair-to-boat conformation in a-linkages of its backbone. Physical integrity of pectin-based electrodes was not challenged during repeated lithiation/delithiation cycles without crack development that was observed in rigid CMC-based electrodes. Covalent bonds formed between carboxylic side chains of pectin and silicon surface oxide prevented active silicon mass from being detached away from electric pathways. However, hydrogen bonds between hydroxyl side chains of amylose and silicon surface oxide were not strong enough to keep the silicon mass electrochemically active after cyclability tests