Air-stable sodium dimethylglyoxime as a cathode presodiation additive for high-energy-density sodium-ion batteries

Cathode presodiation has emerged as a crucial strategy to address the initial sodium loss that severely limits the initial coulombic efficiency and energy density of sodium-ion batteries. However, existing presodiation additives suffer from intrinsic drawbacks including poor air stability, mismatched decomposition potentials, and undesirable gas evolution which critically hinder their practical application. Herein, we present sodium dimethylglyoxime (Na₂DMGO). By structurally translating oxime-lithium into a sodium-based salt, we cleverly leverage its inherent solubility as a unique advantage, delivering a robust and gas-free presodiation additive. Na₂DMGO delivers a sodium release capacity of 330 mAh g^-1 and decomposes at 3.4 V. In situ Fourier-transform infrared spectroscopy and differential electrochemical mass spectrometry analyses confirm its complete, gas-free decomposition into non-toxic DMODO via a C[double bond, length as m-dash]N bond cleavage pathway. When 5 wt% Na₂DMGO is incorporated into a Na₃V₂(PO₄)₃ cathode and paired with a hard carbon anode, the capacity retention improves from 62% to 85% and this improvement is accompanied by an increase in energy density from 117 to 131.5 Wh kg^-1 (based on the mass of the active material only). These results highlight Na₂DMGO as a practical and scalable sodium-supplementing additive that effectively mitigates irreversible Na⁺ loss.