A P2-NaxCo0.7Mn0.3O2 (x ≈ 1.0) cathode material for Na-ion batteries with superior rate and cycle capability

Abstract

The development of sodium ion batteries is of key importance in future energy technology, but so far no materials are known with sufficient rate and cycle capability for real applications. Here we report on a P2-Na_xCo_0.7Mn_0.3O₂ (x ≈ 1.0) cathode material with outstanding properties composed of layered hexagonal nanosheets synthesized using a simple and scalable co-precipitation and solid state reaction method. The material has excellent cycle capability with 84% capacity retention after 225 cycles at 1C rate, and an extraordinary rate capability with ∼75% of the 1C capacity maintained even at a very high charge/discharge rate of 30C. The unique properties may be attributed to a combination of the layered structure and the nanosheet morphology that mitigates the stress caused by Na ion diffusion during cycling. Moreover, the nanosheets are highly (001) oriented, leading to a large active surface of (010)/(100) planes, which could facilitate easy Na ion extraction/intercalation.