Positive electrode-active substance for sodium secondary cell, positive electrode for sodium secondary cell, and sodium secondary cell
A positive electrode-active material is provided for use in a positive electrode for a sodium secondary cell and a sodium secondary cell. Also provided is a positive electrode for a sodium secondary cell and a sodium secondary cell having a high energy density. The positive electrode-active material for a sodium secondary cell includes a composite metal oxide, which has an α-NaFeO 2 type crystal structure and is denoted by Formula (1) described below: Na a (Fe w Ni x Mn y-z Ti z )O 2 (1), wherein a is greater than or equal to 0.6 and less than or equal to 1.0, w is greater than 0 and less than 0.5, x is greater than 0 and less than 0.5, y is greater than 0.03 and less than or equal to 0.5, z is greater than or equal to 0.03 and less than 0.5, and w+x+y=1.0, and y>z.
1. A positive electrode-active material for a sodium secondary cell including a composite metal oxide which has an α-NaFeO 2 type crystal structure and is represented by Formula (1) described below,
Na a (Fe w Ni x Mn y-z Ti z )O 2 (1)
wherein a is greater than or equal to 0.6 and less than or equal to 1.0, w is greater than 0 and less than 0.5, x is greater than 0 and less than 0.5, y is greater than 0.03 and less than or equal to 0.5, z is greater than or equal to 0.03 and less than 0.5, w+x+y=1.0, and y>z.
2. The positive electrode-active material for a sodium secondary cell according to claim 1 , wherein z is less than or equal to 0.3.
3. The positive electrode-active material for a sodium secondary cell according to claim 1 , wherein y is greater than or equal to 0.2.
4. The positive electrode-active material for a sodium secondary cell according to claim 1 , wherein w is greater than or equal to 0.15 and less than or equal to 0.45.
5. The positive electrode-active material for a sodium secondary cell according to claim 1 , wherein a, w, x, and y satisfy the relationship of a+3w+2x+4y=4.
6. A positive electrode for a sodium secondary cell which contains the positive electrode-active material for a sodium secondary cell according to claim 1 .
7. A sodium secondary cell, comprising:
a positive electrode;
a negative electrode; and
a nonaqueous electrolyte,
wherein the positive electrode is the positive electrode for a sodium secondary cell according to claim 6 .
8. The sodium secondary cell according to claim 7 , further comprising:
a nonaqueous electrolyte solution in which the nonaqueous electrolyte is dissolved in an organic solvent,
wherein the organic solvent includes an organic solvent having a fluorine substituent group.
9. The sodium secondary cell according to claim 8 , wherein the organic solvent having the fluorine substituent group is 4-fluoro-1,3-dioxolan-2-one.
10. The sodium secondary cell according to claim 7 further comprising:
a separator arranged between the positive electrode and the negative electrode.
11. The sodium secondary cell according to claim 10 , wherein the separator includes a laminated porous film in which a heat-resistant porous layer containing a heat-resistant resin and a porous film containing a thermoplastic resin are laminated.