Sustainable and robust biomass-based binder for silicon anodes in lithium-ion batteries: cross-linked sodium alginate and chondroitin sulfate

Silicon (Si) is a promising next-generation anode material for lithium-ion batteries (LIBs) due to its exceptionally high theoretical capacity (3579 mAh g^{- 1}) and natural abundance. However, its commercialization remains challenging due to severe volume expansion (~300%) during cycling, leading to poor structural stability and rapid capacity degradation. To address this issue, we developed a novel biomass-derived binder system denoted as SCC, composed of sodium alginate (SA) and chondroitin sulfate (CS), crosslinked via a simple calcium chloride (CaCl₂) aqueous treatment. Unlike conventional synthetic polymer-based binders, this system enhances mechanical stability while maintaining an environmentally friendly, water-based fabrication process. Spectroscopic analysis confirmed strong hydrogen bonding interactions between SA and CS, as well as robust crosslinking formation through Ca²⁺. These interactions effectively enhance the mechanical strength of the SCC binder, enabling it to accommodate the severe volume changes that occur during electrochemical reactions in Si anodes. This, in turn, contributes to enhanced structural stability of Si electrode, which leads to a reduction in both solid electrolyte interphase and charge transfer resistance. As a result, the SCC electrode showed improved electrochemical cycling stability, with a 13.45% higher capacity retention after 60 cycles at a 0.2C rate compared to SA alone. This suggests its potential as a sustainable and scalable solution for next-generation high-performance Si anodes.