A universal chemical presodiation strategy using Na-Bpy/DEE is proposed for Na-deficient oxide cathodes under air condition, which promotes formation of uniform and robust NaF-rich interface during presodiation. This minimizes stress accumulation and structure distortion upon Na⁺ intercalation/extraction to exhibit high-capacity retention.

Abstract

Layered transition-metal oxides have attracted growing attention for sodium-ion batteries (SIBs); however, their application is hindered by low initial coulombic efficiency (ICE) due to Na-deficiency and solid-electrolyte interphase formation. Herein, a universal chemical presodiation pathway is reported with Na-bipyridine dissolved in diethyl ether (Na-Bpy/DEE) for stable Na-deficient P2-Na_2/3Ni_1/3Mn_2/3O₂ (NNMO) electrode under air condition. The strongly electron-withdrawing N-functional groups of Bpy^•− radicals endow its air insensitivity, and it reduces the NNMO cathode for compensation of Na⁺ from the weakly solvating DEE. This results in a uniform and robust NaF-rich interface to prevent surface lattice disorder of NNMO, which is caused by local stress, and preserve structure integrity. The presodiated NNMO electrode shows high ICE of 100% and reversible capacity of 158.3 mAh g⁻¹, and its pouch cell coupled with hard carbon presents high-capacity retention of 95.9% after 200 cycles. This work proposes an industrially feasible presodiation strategy to highly efficient SIBs.