Toward Greener Energy Storage: A Sustainable Oxidized Cellulose Binder for Micro-Silicon Anodes as an Alternative to CMC

Abstract Silicon (Si) is a highly researched alternative anode material for lithium-ion batteries (LIBs) due to its tremendous theoretical storage capacity, which has the potential to increase the energy of LIBs. The low-cost and earth-abundant micro-silicon (μ-Si) as the anode material, combined with a green cellulose derivative binder, has been the subject of extensive research for its use in greener batteries. However, during the lithiation and delithiation processes, Si anodes undergo dramatic volume changes, resulting in anode pulverization and delamination, as well as the formation of solid electrolyte interface layers. A 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-catalyzed oxidation with or without chemical treatment of two cellulose led to both 40 and 95% oxidized celluloses with reduced molecular weights (Mw). A low-molecular-weight oxidized treated sample from microcrystalline cellulose (OTMCC, about 3968 g/mol) produces very interesting results compared to sodium carboxymethyl cellulose with a molecular weight of 90 kg/mol (CMC 90). Initial charge capacity was about 1885 and 2256 mAh/g for OTMCC and CMC 90, respectively, and 1369 and 1617 mAh/g after 100 cycles, with equivalent capacity retentions of 72 and 71% using 10% fluoroethylene carbonate additives in the standard electrolyte. The μ-Si anode benefits from OTMCC's crystallinity, smaller size, and strong hydrogen bonding. A mechanical mixture/network of OTMCC and OMCC (1:3 w/w) is shown as the optimum configuration, which maintained 2832 and 1996 mAh/g charge capacities (1st and 100th cycles) with a C-rate of 0.1C. The use of a highly oxidized cellulose as a binder for μ-Si anodes in LIBs may thus improve cycle life and reduce capacity loss, even compared to CMC 90. The carboxyl groups of oxidized cellulose generate strong and highly reversible hydrogen bonds with Si particles, and the mixture of larger and shorter chains creates a more efficient binder for μ-Si.