Composite metal oxide, positive electrode active material, positive electrode, sodium secondary battery, and method for producing composite metal oxide
Provided is a composite metal oxide which is represented by Formula (1) and has an α-NaFeO 2 type crystal structure, in which a peak half value width of a (104) plane to be measured by powder X-ray diffraction is 0.250° or less at 2θ. Na x M 1 r (Fe y Ni z Mn w M 1−y−z−w )O 2±δ (1) (in Formula (1), M represents any one or more elements selected from the group consisting of B, Si, V, Ti, Co, Mo, Pd, Re, Pb, and Bi, M 1 represents any one or more elements selected from the group consisting of Mg and Ca, and relations 0≤r≤0.1, 0.5≤x≤1.0, 0.1≤y≤0.5, 0<z<0.4, 0<w<0.4, 0≤δ≤0.05, and y+z+w≤1 are satisfied).
1. A composite metal oxide which is represented by Formula (1) and has an α-NaFeO 2 type crystal structure,
wherein a peak half value width of a (104) plane to be measured by powder X-ray diffraction is 0.250° or less at 2θ, wherein
Na x M 1 r (Fe y Ni z Mn w M 1−y−z−w )O 2±δ (1)
in Formula (1), M represents any one or more elements selected from the group consisting of B, Si, V, Co, Mo, Pd, Re, Pb, and Bi, M 1 represents any one or more elements selected from the group consisting of Mg and Ca, and relationships 0≤r≤0.1, 0.5≤x≤1.0, 0.1 ≤y≤0.5, 0<z<0.4, 0<w<0.4, 0≤δ≤0.05, and y+z+w≤1 are satisfied.
2. The composite metal oxide according to claim 1 ,
wherein the peak half value width of the (104) plane to be measured by powder X-ray diffraction is less than 0.200° at 2θ.
3. The composite metal oxide according to claim 1 ,
wherein y is greater than or equal to 0.2 and less than or equal to 0.5, z is greater than 0.15 and less than 0.4, and w is greater than 0.15 and less than 0.4.
4. A positive electrode active material comprising:
the composite metal oxide according to claim 1 .
5. A positive electrode comprising:
the positive electrode active material according to claim 4 .
6. A sodium secondary battery comprising:
the positive electrode according to claim 5 .
7. A method for producing a composite metal oxide which has an α-NaFeO 2 type crystal structure and in which a peak half value width of a (104) plane to be measured by powder X-ray diffraction is 0.250° or less at 2θ, the method comprising:
a mixing step of mixing a Na-containing compound, an Fe-containing compound, a Ni-containing compound, a Mn-containing compound, and an M-containing compound having a melting point of 800° C. or lower to obtain a mixture; and
a calcination step of calcining a powder which contains the mixture,
wherein M represents one or more elements selected from the group consisting of B, Si, V, Co, Mo, Pd, Re, Pb, and Bi,
wherein the calcination step includes a first calcination step and a second calcination step, and
the second calcination step is performed at a temperature higher than a temperature of the first calcination step.
8. The method for producing a composite metal oxide according to claim 7 ,
wherein the first calcination step is performed at a holding temperature higher than or equal to 500° C. and lower than or equal to 900° C.,
the second calcination step is performed at a holding temperature higher than or equal to 750° C. and lower than or equal to 1000° C., and
the second calcination step is performed at a holding temperature higher than the holding temperature of the first calcination step.
9. The method for producing a composite metal oxide according to claim 7 ,
wherein the M-containing compound contains a compound having a melting point lower than or equal to the holding temperature of the first calcination step.
10. The method for producing a composite metal oxide according to claim 7 ,
wherein the M-containing compound contains B.