Aqueous Guar Gum Binder Enables Regulated Surface Structure Evolution and Enhanced Electrochemical Performance of NFPP/Activated Carbon Composite Cathodes for Sodium-Ion Batteries.

Abstract

Na4Fe3(PO4)2(P2O7) (NFPP) has emerged as a promising low-cost, structurally stable cathode material for sodium-ion batteries. However, the intrinsically low electronic conductivity of NFPP limits NFPP/activated carbon (NFPP/AC) composite performance. Considering that polymer binders control electrode microstructures and sodium-ion reaction kinetics, the authors incorporated an aqueous guar gum (GG) binder into an NFPP/AC cathode and benchmarked it against polyvinylidene fluoride (PVDF) and carboxymethyl cellulose (CMC)/styrene-butadiene rubber (SBR) systems. The GG-based electrode slurry demonstrates superior rheological properties that facilitate electrolyte infiltration, promote uniform particle dispersion and improve electrode structural integrity. This effect is primarily ascribed to the hydroxyl-rich structure of GG, which establishes hydrogen-bond-mediated multipoint interfacial interactions between NFPP and AC particles, enhancing particle dispersion, slurry structural recovery and interparticle contact. GG also promotes a uniform, dense, inorganic-rich cathode-electrode interface, minimizing charge-transfer resistance and activation energy (61.1 kJ·mol-1). Consequently, the GG-based electrode maintains a high Na+ diffusion coefficient during cycling, retaining 73.8 mAh·g-1 at 5C and showing negligible capacity fading after 400 cycles at 1C. Overall, GG constructs a continuous interfacial binding network between NFPP and AC, regulating interfacial chemistry, structural integrity and Na+ transport pathways.

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