| abstract |
One aspect of the present invention provides a method comprising: manufacturing a sodium ion secondary cell having an anode and a cathode, the anode comprising a negative electrode active material comprising disordered carbon on an anode substrate, and the cathode comprising a comprising a nickel-containing sodium oxide positive electrode active material on a cathode substrate; and in a cycling phase, charging the cell to a first voltage; wherein the ratio of the mass of the negative electrode active material to the mass of the positive electrode active material is greater than 0.37 and is less than 1.2. |