Novel copper redox-based cathode materials for room-temperature sodium-ion batteries

Layered oxides of P2-type Na_0.68Cu_0.34Mn_0.66O₂, P2-type Na_0.68Cu_0.34Mn_0.50Ti_0.16O₂, and O'3-type NaCu_0.67Sb_0.33O₂ were synthesized and evaluated as cathode materials for room-temperature sodium-ion batteries. The first two materials can deliver a capacity of around 70 mAh/g. The Cu²⁺ is oxidized to Cu³⁺ during charging, and the Cu³⁺ goes back to Cu²⁺ upon discharging. This is the first demonstration of the highly reversible change of the redox couple of Cu²⁺/Cu³⁺ with high storage potential in secondary batteries.