An Eco-Friendly Water-Soluble Composite Binder with Sulfate- and Cyanide- Functionalized for Stabilizing 4.6 V LiCoO ₂ Cathodes

Lithium cobalt oxide (LCO) is a typical layered structure cathode material for high-energy-density lithium-ion batteries. However, its structural instability at high voltages limits the operational voltage window in practical applications. In this study, a water-soluble composite binder, poly(acrylamide-co-acrylonitrile)-carrageenan (PMN-CRN), was designed and synthesized for application in high-voltage cathodes. The binder consists of PMN, a water-soluble polymer produced by copolymerizing acrylamide (AM) and acrylonitrile (AN), and λ-carrageenan (CRN), a natural polysaccharide enriched with sulfate groups, which are blended to build a 3D cross-linked network structure through hydrogen-bonding interactions. This structure is suitable for electrode slurry processing and stabilizing the interface construction. The PMN-CRN enhances the stability of the cathode solid electrolyte interface (CEI) and effectively inhibits the structural collapse and irreversible phase transitions at high voltages, thereby improving the interfacial stability and cycling durability of the electrodes. The capacity retention rate of LCO@PMN-CRN reaches 94.6% after 200 cycles at 1C, and maintains a reversible capacity of approximately 150 mAh g–1 at 5C. The outstanding electrochemical performance indicates that the PMN-CRN binder effectively stabilizes 4.6 V LCO cathode, which has the potential to be applied to high-energy-density lithium-ion batteries.