A heterocatalyst-modified separator enables multi-stage sodium compensation for long-life sodium-ion batteries

Irreversible sodium loss, primarily caused by solid electrolyte interphase (SEI) formation during initial cycling, significantly degrades the capacity of sodium-ion batteries by depleting active sodium. While pre-sodiation mitigates initial sodium loss, it fails to address continuous loss throughout the battery lifecycle. To overcome this limitation, we propose a sustained sodium compensation strategy utilizing activation-releasing systems. Key to this approach are high-capacity sodium compensators, Na2C2O4 and Na2C4O4, supported on a B and N co-doped Mo2C-W2C (MoW-C) heterostructure catalyst. This configuration enables efficient sodium release at charging voltages of 3.53 and 3.78 V, respectively. By integrating the sodium supplement agent onto the separator, and precisely controlling voltage and charge, multiple sodium replenishment is achieved over the entire battery lifecycle. This strategy reduces initial active sodium loss by 36.53%. Furthermore, a single activation during subsequent usage provides an additional 0.115 mAh cm−2 of active sodium. As a result, the cell exhibits exceptional cycling stability, with a capacity loss of only 0.059% per cycle over 350 cycles at 0.5 C.