Electrode active material for sodium secondary battery, electrode for sodium secondary battery, sodium secondary battery and method for producing composite metal oxide

1. An electrode active material for a sodium secondary battery, comprising:

a composite metal oxide,

wherein the electrode active material has an α-NaFeO 2 type crystal structure, which is a layered rock salt type crystal structure,

Na a M 1 r M b Ni e Si c O d   (1)

where M represents one or more elements selected from the group consisting of B, Ti, Mn, Fe, and Co, M 1 represents one or more elements selected from the group consisting of Mg, Ca, and Sr, and relations 0≤r≤0.1, 0.5≤a≤1.0, 0<c<0.1, 0.5<b+c≤1.1, 0<e≤0.5, and 1.95<d<2.05 are satisfied, and

where a peak intensity of a (200) plane of nickel oxide of a powder X-ray diffraction spectrum using CuKα radiation is set as I, and a peak intensity of a (104) plane of the composite metal oxide represented by Formula (1) is set as I 0 ,I/I 0 obtained by dividing I by I 0 is greater than or equal to 0.015 and less than or equal to 0.1 or less.

2. The electrode active material for a sodium secondary battery according to claim 1 ,

wherein M in Formula (1) contains at least one element selected from the group consisting of Ti, Mn, and Fe.

3. The electrode active material for a sodium secondary battery according to claim 1 ,

wherein a crystal structure of the composite metal oxide represented by Formula (1) has a layered structure.

4. An electrode comprising:

the electrode active material for a sodium secondary battery according to claim 1 .

5. A sodium secondary battery comprising:

the electrode according to claim 4 .

6. A method for producing a composite metal oxide, comprising:

a mixing step of mixing a Na-containing compound, a Ni-containing compound, an M-containing compound (M represents any one or more elements selected from the group consisting of B, Ti, Mn, Fe, and Co), and a Si-containing compound to obtain a mixture; and

a calcination step of calcining powder containing the mixture,

wherein the mixing is carried out such that a mass of the Si-containing compound is set to be greater than 0 and less than or equal to 3 parts by mass in a case where a total mass of the Na-containing compound, the Ni-containing compound, and the M-containing compound is set to 100 parts by mass,

wherein the electrode active material has an α-NaFeO 2 type crystal structure which is a layered rock salt type crystal structure,

wherein the composite metal oxide is represented by Formula (1):

Na a M 1 r M b Ni e Si c O d   (1)

where M represents one or more elements selected from the group consisting of B, Ti, Mn, Fe, and Co, M 1 represents one or more elements selected from the group consisting of Mg, Ca, and Sr, and relations 0≤r≤0.1, 0.5≤a≤1.0, 0<c<0.1, 0.5<b+c≤1.1, 0<e≤0.5, and 1.95<d<2.05 are satisfied, and

where a peak intensity of a (200) plane of nickel oxide of a powder X-ray diffraction spectrum using CuKα radiation is set as I, and a peak intensity of a (104) plane of the composite metal oxide represented by Formula (1) is set as I 0 ,I/I 0 obtained by dividing I by I 0 is greater than or equal to 0.015 and less than or equal to 0.1 or less.

7. The method for producing a composite metal oxide according to claim 6 ,

wherein the Si-containing compound is a silicon-containing oxide.

8. The method for producing a composite metal oxide according to claim 6 ,

wherein the M-containing compound contains at least one element selected from the group consisting of Ti, Mn, and Fe.

9. The method for producing a composite metal oxide according to claim 6 ,

wherein a calcination temperature in the calcination step is higher than or equal to 800° C. and lower than or equal to 1000° C.

10. The method for producing a composite metal oxide according to claim 9 ,

wherein a holding time at the temperature higher than or equal to 800° C. and lower than or equal to 1000° C. in the calcination step is longer than or equal to 4 hours and shorter than or equal to 20 hours.