Multi-component surface engineering of Na 3 V 2 (PO 4 ) 2 O 2 F for low-temperature (-40 °C) sodium-ion batteries.

A functional Na 3 V 2 (PO 4 ) 2 O 2 F (NVPOF) cathode with a multi-component (Na 3 V(PO 4 ) 2 , V 2 O 3 , 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.