Designing Cellulose Triacetate-Based Universal Binder for High-Voltage Sodium-Ion Battery Cathodes with Enhanced Ionic Conductivity and Binding Strength.

Abstract

Binders play a pivotal role in the performance of sodium-ion battery (SIB) cathodes, but traditional binders often struggle to balance broad compatibility, high ionic conductivity, superior binding strength, and environmental sustainability. In this study, a universal cellulose triacetate (TAC)-based binder (TAC-MMT) composed of TAC and natural montmorillonite (MMT) is designed to facilitate rapid Na⁺ transport pathways and establish a robust hydrogen-bonding network. This innovative TAC-MMT binder features a unique chemical structure that achieves high ionic conductivity through a self-enrichment and fast-transport mechanism, while its superior binding strength is attributed to hydrogen-bonding crosslinks between proton acceptors (C═O) in TAC and proton donors (-OH) in MMT. More importantly, the outstanding solubility and film-forming properties of TAC-MMT contribute to stable electrode protection and broad compatibility with high-voltage SIB cathodes. Benefiting from these advantages, the Na₃V₂(PO₄)₂O₂F (NVPOF) electrodes with the TAC-MMT binder demonstrate exceptional performance, including a high capacity retention of 95.2% over 500 cycles at 5C and a rapid rate response of up to 15C. The versatility of the TAC-MMT binder is further confirmed with high-voltage NaNi_1/3Fe_1/3Mn_1/3O₂ and Na_0.61[Mn_0.27Fe_0.34Ti_0.39]O₂ cathodes. This study highlights the potential of biomass-based binders as a sustainable and effective solution for advancing high-performance sodium-ion batteries.