Enhanced cycle stability of Na0.9Ni0.45Mn0.55O2 through tailoring O3/P2 hybrid structures for sodium-ion batteries

A critical challenge for the practical use of the layered O3-type binary nickel manganese oxides for sodium-ion batteries is the poor structural stability during extended cycling. The approaches of constructing O3/P2 hybrid composites can partially improve the cycling stability, but general approaches sacrifice the advantages of high capacity and low cost of the O3-type cathodes due to excessive sodium deficiency and lithium substitution. Here, we rationally design a serial of novel O3-majority hybrid Na0.9-xNi0.45Mn0.55O2 (x = 0.02, 0.04 and 0.08) cathodes, which exhibit high capacities while maintaining exceptional long-term stability. Particularly, the optimized O3/P2 Na0.88Ni0.45Mn0.55O2 composite delivers 106.7 mA h·g−1 with 71.1% capacity retention after 250 cycles at 1 C (1C = 150 mA g−1), the cyclability is 32% higher than that of the O3Na0.9Ni0.45Mn0.55O2 cathode; and it also delivers a initial discharge capacity of 75.9 mA h·g−1, maintaining 72.4% capacity retention after 1000 cycles at 10 C. More importantly, the post-cycling analyses demonstrate O3/P2 hybrid phases successfully suppress the structural degradation of Na0.9Ni0.45Mn0.55O2 during battery operation. This study provides new perspectives in designing high performance cathodes for sodium-ion batteries.