Non-aqueous electrolyte secondary battery and method of manufacturing the same

1. A non-aqueous electrolyte secondary battery comprising: a negative electrode, a non-aqueous electrolyte comprising a carbonate-based solvent containing a lithium salt, and a positive electrode having a positive electrode active material comprising sodium oxide, characterized in that:

the sodium oxide is represented by the general formula Na a Li b M x O 2±α , where 0.5≦a≦1.0, 0<b<0.5, 0.6≦a+b≦1.1, 0.90≦x≦1.10, and 0≦α≦0.1, and M is at least one element selected from the group consisting of manganese, iron, cobalt, and nickel; and the sodium oxide has a main peak at 2θ=15.9° to 16.9° as determined by X-ray powder crystal diffraction (Cukα).

2. A non-aqueous electrolyte secondary battery comprising: a negative electrode, a non-aqueous electrolyte comprising a carbonate-based solvent containing a lithium salt, and a positive electrode having a positive electrode active material comprising sodium oxide, characterized in that:

the sodium oxide contains lithium; the sodium oxide has a main peak at 2θ=17.5° to 19.0° and sub-peaks at 35.5° to 37.5° and 66.0° to 67.5°, as determined by X-ray powder crystal diffraction (Cukα) measured at the time when the battery is charged to 25% to 50% of the battery capacity after manufacture of the battery; and the sodium oxide is represented by the general formula Na a Li b Mn y Co z O 2±α where 0<a≦0.7, 0<b<1.0, 0.6≦a+b≦1.1, 0.45≦y≦0.55, 0.45≦z≦0.55, 0.90≦y+z≦1.10, and 0≦α≦0.1.

3. The non-aqueous electrolyte secondary battery according to claim 2 , wherein the potential of the positive electrode at end of charge is 4.5 V or higher versus metallic lithium.

4. The non-aqueous electrolyte secondary battery according to claim 2 , wherein a negative electrode active material for the negative electrode comprises at least one substance selected from the group consisting of metallic lithium, silicon, carbon, tin, germanium, aluminum, lead, indium, gallium, a lithium-containing alloy, a lithium-intercalated carbon material, a lithium-intercalated silicon material, and a compound containing lithium and carbon.

5. The non-aqueous electrolyte secondary battery according to claim 3 , wherein a negative electrode active material for the negative electrode comprises at least one substance selected from the group consisting of metallic lithium, silicon, carbon, tin, germanium, aluminum, lead, indium, gallium, a lithium-containing alloy, a lithium-intercalated carbon material, a lithium-intercalated silicon material, and a compound containing lithium and carbon.