Copper substituted P2-type Na0.67CuxMn1−xO2: a stable high-power sodium-ion battery cathodeElectronic supplementary information (ESI) available: SEM images and additional electrochemical characterization. See DOI: 10.1039/c5ta06371j

While sodium-ion batteries (SIBs) are considered as a next-generation energy storage device because of the higher abundance and lower cost of sodium compared to those of lithium, developing high-power and stable cathode materials remains a great challenge. Here, micron-sized plate-like copper-substituted layered P2-type Na 0.67 Cu x Mn 1− x O 2 is demonstrated to rapidly charge and discharge within 5 minutes while giving a capacity of more than 90 mA h g −1 , corresponding to a half-cell energy density of 260 W h (kg cathode) −1 at a power density of 3000 W (kg cathode) −1 , which is comparable to that of high-power lithium-ion cathodes. The materials show excellent stability, retaining more than 70% of the initial capacity after 500 cycles at 1000 mA g −1 . The good cycle and rate performances of the materials are attributed to copper in the lattice, which stabilizes the crystal structure, increases the average discharge potential and improves sodium transport. This makes Na 0.67 Cu x Mn 1− x O 2 an ideal choice as a cathode for high-power sodium-ion batteries. Plate-like copper-substituted P2-type Na 0.67 Cu x Mn 1− x O 2 is able to rapidly charge and discharge within 5 minutes while still giving a capacity of about 90 mA h g −1 at a current of 1000 mA g −1 .