Strategy Formulation for Mitigating Capacity Fading of Na‐Layered Oxides

Abstract The mechanisms underlying capacity fading during cycling in layered oxide cathode materials for sodium‐ion batteries remain inadequately understood. It is essential to elucidate the reasons and propose effective strategies. Here, the capacity‐fading mechanism of commercial NaFe 1/3 Mn 1/3 Ni 1/3 O 2 is due to the dissolution of iron ions. Additionally, the extraction of sodium ions (after the Fe 3+ /Fe 4+ reaction) lowers the energy level of NaFe₁/₃Mn₁/₃Ni₁/₃O₂ below that of the electrolyte solvent, thereby inducing solvent decomposition. We establish screening criteria for electrolyte additives through theoretical calculations to improve capacity retention. We identified a series of nitrogen‐containing Lewis base additives that can kinetically bind efficiently to iron ions in NaFe₁/₃Mn₁/₃Ni₁/₃O₂ and thermodynamically exhibit stronger electron‐donating abilities than the solvents. A new compound, sodium bis(trimethylsilyl)amide (which has not been studied as a Na‐ion battery additive before), is selected through the Reaxys database (out of 61 molecules) because it is commercially available at a low price and is relatively stable in the electrochemical process. Such an additive is demonstrated to greatly improve the Coulombic efficiency and reduce the dissolution of iron ions of NaFe₁/₃Mn₁/₃Ni₁/₃O₂//hard carbon cells.