Activation of residual sodium via in situ neutralization toward practical layered oxides

Abstract

Layered oxide cathodes for sodium-ion batteries face challenges from surface residual alkalis, which degrade electrochemical performance and slurry processability. Herein, we propose an in situ acid–base neutralization strategy that converts inactive residual alkali into an active sodium compensation additive, disodium iminodiacetate (IDA-2Na), via treatment with iminodiacetic acid. This approach not only alleviates slurry gelation, but also repurposes residual alkali to supplement sodium loss from SEI formation. When applied to P2-Na_2/3Ni_1/3Mn_1/3Ti_1/3O₂, the modified cathode delivers a significantly improved specific capacity (154.6/124.6 mAh g⁻¹ at 0.05C), rate capability (75.6 mAh g⁻¹ at 10C), and cycling stability. Full cells with a hard carbon anode achieve a higher discharge capacity (89.2 mAh g⁻¹) and energy density (234.52 Wh kg⁻¹), along with enhanced capacity retention (81.3% after 300 cycles). This work offers a practical and effective surface modification strategy to advance the commercialization of high-performance layered oxide cathodes for sodium-ion batteries.