Engineering an Adaptive Inner Helmholtz Plane Enables High-Voltage Sodium-Ion Batteries

Elevating the cutoff voltage of layered oxide cathodes (LOCs) is an indispensable way to achieve high-energy-density sodium-ion batteries (SIBs). However, undesired interfacial parasitic reactions impede the stable operation of LOCs at high voltages. Herein, we rationally designed an adaptive inner Helmholtz plane (IHP) to regulate the interfacial chemistry of the LOCs. An electron-deficient ligand was employed to anchor with the anions and expel the free solvents within the IHP of LOCs at high voltages, thereby preventing anionic decomposition of the electrolytes and reducing HF generation. Moreover, the anion-anchored IHP facilitates the formation of a robust inorganic-rich cathode electrolyte interphase (CEI) on the LOCs. Benefiting from the tailored IHP, O3-NaNi_1/3Fe_1/3Mn_1/3O₂ (NNFMO) exhibits significantly enhanced cycling stability at an ultrahigh voltage of 4.5 V. Our work paves a new way for regulating interfacial chemistry by tailoring the electric double layer of LOCs for high-energy and long-life SIBs.