Water-Soluble Elastomeric Carboxymethyl Chitosan as an Efficient Binder for Si Anodes of Lithium Ion Batteries

The binder acts a pivotal part in determining the mechanical and electrochemical performances of lithium-ion battery electrodes. Herein, a series of water-soluble Si anode binders based on carboxymethyl chitosan (C-Cs) and styrene-butadiene rubber (SBR) is developed. Water-soluble C-Cs and aqueous emulsion SBR solution are mixed to form C-Cs/SBR binders. The physical properties of the modified Si electrode are investigated through electrolyte swelling test, peeling test, and scanning electron microscopy. The mechanical strength provided to Cu foils and active substances by the C-Cs/SBR binder is higher than that produced by C-Cs. This performance can effectively reduce the stress/strain caused by the drastic volume change of the Si anodes during repeated uses and improve the electrochemical property of lithium-ion batteries. The initial thicknesses of the Si electrodes with polyvinylidene fluoride, C-Cs, and C-Cs/SBR₂₀ binders are approximately 7.1, 7.2, and 6.9 µm, respectively. After 100 cycles, their initial thicknesses increase to 11.2, 12.4, and 7.2 µm and correspond to expansions of 57.8%, 72.2%, and 4.3%, respectively. The discharge capacity of Si electrodes containing C-Cs/SBR₂₀ binder reaches to 1340 mAh·g^-1 when the current density is 4 A·g^-1, and reserves to be 1020 mAh·g^-1 after undergoing 400 cycles of repeated use at 500 mA·g^-1.