Novel high energy density sodium layered oxide cathode materials: from material to cells

A limitation of sodium ion batteries is their low energy density in comparison to lithium ion batteries, therefore Sharp Laboratories of Europe Ltd have been developing higher energy density sodium ion batteries utilizing a high specific capacity cathode, NaNi_1/3Fe_1/6Mn_1/3Mg_1/12Sn_1/12O₂, which has been optimized for capacity and voltage, against a pristine hard carbon anode. The development of a full sodium ion cell and the optimization for energy density is discussed, and we report a 3.3 Ah cell with a demonstrated cell energy density of 211 Wh/L with 94% capacity retention after 150 cycles, and a 4.2 Ah cell with a demonstrated cell energy density of 252 Wh/L. The hard carbon is not pre-cycled and therefore the cells exhibit a 20% loss during the formation stage. These results represent realistic values for larger scale sodium ion battery manufacture as a drop-in technology for lithium ion batteries.