Potential-dependent interfacial specific adsorption accelerates charge transfer in sodium-ion batteries.

Abstract

Fast-charging capabilities of sodium-ion batteries have emerged as a pivotal objective within the energy storage fields. Sodium layered P2-type oxide positive electrodes are considered promising for fast charging due to their inherent fast Na⁺ mobility. However, their electrochemical polarization and interfacial charge transfer especially at high state of charge are limiting factors in quick kinetic response for large current. Herein, we demonstrate that a typical P2-type positive electrode (Na_0.7Ni_0.27Mn_0.53Cu_0.04Fe_0.08Ti_0.08O₂) achieves high-rate capacities through avoiding octahedral stacking faults, maintaining lattice oxygen activity and controlling anion-specific adsorption. The intermediate Z-phase intergrowth structure mitigates kinetic polarization and thermodynamic hysteresis by simultaneously suppressing the unfavorable phase evolution from P2-type to O2-type and irreversible oxygen redox. The potential-dependent competitive adsorption mechanism between anions and solvent molecules is revealed within the inner Helmholtz plane, where optimized anion-specific adsorption elevates potential difference between electrodes and inner Helmholtz plane, accelerating charge transfer across the electrode/electrolyte interface. Furthermore, the F-rich cathode/electrolyte interphase generated from inner Helmholtz plane mitigates transition metal dissolution and surface lattice collapse for stable long-term cycling. This study highlights the synergistic coupling interaction between bulk phase stability and interfacial environment optimization in ensuring fast Na⁺/charge transport kinetics for sodium-ion batteries.