Multi-component surface engineering of Na₃V₂(PO₄)₂O₂F for low-temperature (-40 °C) sodium-ion batteries

A functional Na₃V₂(PO₄)₂O₂F (NVPOF) cathode with a multi-component (Na₃V(PO₄)₂, V₂O₃, and reduced graphene oxide) surface coating is developed via a facile hydrothermal reaction followed by calcination, and exhibits high reversible capability, and long-term cycling stability even at a low temperature of -40 °C. It is demonstrated that the multi-component-coating layer can significantly accelerate the e^-/Na⁺ transport and reduce the interfacial resistance at low temperature. This work provides a novel strategy to boost the kinetics and stability of electrode materials for low-temperature sodium ion batteries.