High-efficiency NaCl presodiation agent for sodium-ion batteries

In the ordinary sodium-ion batteries, irreversible sodium loss during the initial cycle is inevitable, significantly reducing the initial Coulombic efficiency and operational lifespan. In this work, sodium chloride (NaCl) was developed as a low-cost, non-toxic and high-efficient presodiation agent for Na-ion batteries. The facilely prepared NaCl/Ketjen Black composite can deliver a presodiation capacity of 457 mAh g⁻¹ below 4.2 V. Innovatively, instead of direct cathode incorporation, NaCl is applied as a presodiation layer on commercial polypropylene separators, ensuring homogeneous sodium compensation while avoiding structural damage to the Na₃V₂(PO₄)₃ cathode. In Na₃V₂(PO₄)₃||hard carbon full cells, this approach fully offsets initial sodium loss, achieving a 46.8 % increase in initial discharge capacity (115 mAh g⁻¹) and an ideal 100 % initial Coulombic efficiency. Mechanistic studies confirm NaCl's irreversible decomposition without harmful Cl₂ byproducts, while residual Cl species do not impede charge transfer. The strategy boosts energy density by 29 % (186 Wh kg⁻¹) and demonstrates scalability for practical applications. This work presents a cost-effective and industrially scalable strategy to mitigate irreversible sodium loss, advancing the development of high-energy-density and long-cycle-life sodium-ion batteries.