Optimising Orbital Hybridization Induced Quenching Multistage Phase Transitions and Enhancing Redox Kinetics for Ultralow-Temperature (−70 °C) Sodium Storage

Abstract

The unfavorable phase transitions and sluggish low-temperature kinetics dramatical constrain the application of sodium-ion batteries (SIBs). The deep-seated relationship between the unfavorable phase transition and low-temperature kinetics of pouch cell need to be well revealed. Herein, Zinc (Zn)-doping is introduced to optimize the hybridization of oxygen (O) 2p and transition metal (TM) 3d orbitals in Na_0.67Ni_0.16Co_0.16Mn_0.67O₂. This increases the degree of disorder between the Zn 3d and manganese (Mn) 3d states near the Fermi level, thereby disrupting the ordering of Na⁺ vacancies, forestalling multiphase transitions (P2’ and OP4) and the Jahn–Teller distortion. Remarkably, this approach simultaneously enhances the redox reversibility of cathode materials while mitigating irreversible TM migration. Through optimized orbital hybridization, the activation energy and impedance are significantly reduced, accelerating the rapid storage of Na⁺ at ultralow temperature (−70 °C). The hardcarbon || Na_0.67Ni_0.16Co_0.16Mn_0.65Zn_0.03O₂ (RMNC-2) pouch cell exhibits great practical potential with high average capacity (486 mAh), high energy density (207 Wh kg⁻¹ based on total weight of cathodes and anodes), and durability for low temperature. This research offers valuable insights into up-recycling spent cathodes of lithium-ion batteries (LIBs) for sustainable cathodes of SIBs in pouch cells, with a particular focus on their compatibility across ultralow temperature.