High Capacity O3-Type Na[Li0.05(Ni0.25Fe0.25Mn0.5)0.95]O2 Cathode for Sodium Ion Batteries

In this work we report Na[Li0.05(Ni0.25Fe0.25Mn0.5)0.95]O2 layered cathode materials that were synthesized via a coprecipitation method. The Na[Li0.05(Ni0.25Fe0.25Mn0.5)0.95]O2 electrode exhibited an exceptionally high capacity (180.1 mA h g–1 at 0.1 C-rate) as well as excellent capacity retentions (0.2 C-rate: 89.6%, 0.5 C-rate: 92.1%) and rate capabilities at various C-rates (0.1 C-rate: 180.1 mA h g–1, 1 C-rate: 130.9 mA h g–1, 5 C-rate: 96.2 mA h g–1), which were achieved due to the Li supporting structural stabilization by introduction into the transition metal layer. By contrast, the electrode performance of the lithium-free Na[Ni0.25Fe0.25Mn0.5]O2 cathode was inferior because of structural disintegration presumably resulting from Fe3+ migration from the transition metal layer to the Na layer during cycling. The long-term cycling using a full cell consisting of a Na[Li0.05(Ni0.25Fe0.25Mn0.5)0.95]O2 cathode was coupled with a hard carbon anode which exhibited promising cycling data including a 76% capacity retention over 200 cycles.