Lambda Carrageenan as a Water-Soluble Binder for Silicon Anodes in Lithium-Ion Batteries

The large volume expansion of a silicon (Si) anode causes severe mechanical failure, limiting its use in lithium-ion batteries (LIBs). Using functional polymers as a binder material is an approach to this issue. We explore the applicability of the water-soluble natural polysaccharide lambda carrageenan (CGN) as a binder for Si nanoparticles in LIBs. The characteristic binder properties of commercial (CGN-com) and custom (ext-CGN) CGNs are investigated. CGN binders exhibit excellent mechanical characteristics, remarkable interfacial adhesion, and strong cohesion. The high density of sulfonyl groups in CGN improves the lithium-ion transport kinetics; CGN effectively buffers the volume expansion of Si during alloying, enhancing cycling and rate performance. After 300 cycles at 0.5 C, the Si@CGN electrode delivers a reversible capacity of 1623.75 mAh g–1 and a rate capability of 2143.72 mAh g–1 at 5 C. The electrochemical performance of Si@CGN-ext is about 91% of that of Si@CGN-com. Under all test conditions, both outperformed Si anodes made with traditional binders. When paired with the commercial NCM811 cathode, full cells using Si@CGN-com and Si@CGN-ext have capacities of 79.96 and 75.68 mAh g–1, respectively, and superior stability for 50 cycles. This study reveals the potential of CGN as a low-cost, sustainable binder for Si anodes.