Oxidized λ-Carrageenan as an Aqueous Silicon-Anode Polymer Binder with Reduced Viscosity for Lithium-Ion Batteries

λ-Carrageenan (L-CGN) exhibits high potential as a Si-anode binder due to its high adhesive strength and 3D structure with Si. This study aimed to improve the mechanical properties and reduce the high viscosity of polysaccharides, including L-CGN, by oxidation. The aldehyde functional group introduced via oxidation served as a hinge, providing flexibility to relatively stiff polysaccharide binders and strengthening their interactions with the Si active materials. The oxidized CGN binders exhibited enhanced adhesion and mechanical strength, thereby maintaining the electrode integrity against Si's volume expansion. The Si@Ox-L-CGN electrode, combining oxidized L-CGN (Ox-L-CGN) as a binder and 350 nm-sized Si as an active material, displayed enhanced mechanical properties compared to those of the Si@L-CGN electrode. Si@Ox-L-CGN-5, oxidized by 5% relative to Si@L-CGN, showed an improved initial Coulombic efficiency of 78.6% compared to that of Si@L-CGN (72.6%). Furthermore, at a Si loading level of 1.0 mg cm–2, Si@Ox-L-CGN-5 displayed a capacity of 2032 mAh g–1 after 100 cycles (compared to a very low value of 248 mAh g–1 for Si@L-CGN) and a high capacity retention of 73.9%. The results highlight the potential of Ox-L-CGN as a binder for Si anodes with a large particle size and a high loading level.