Cathode active material, cathode and nonaqueous secondary battery
A cathode active material of the present invention is a cathode active material having a composition represented by General Formula (1) below, LiFe 1-x M x P 1-y Si y O 4 (1), where: an average valence of Fe is +2 or more; M is an element having a valence of +2 or more and is at least one type of element selected from the group consisting of Zr, Sn, Y, and Al; the valence of M is different from the average valence of Fe; 0<x≦0.5; and y=x×({valence of M}−2)+(1−x)×({average valence of Fe}−2). This provides a cathode active material that not only excels in terms of safety and cost but also can provide a long-life battery.
1. A cathode active material having a composition represented by General Formula (1) below,
LiFe 1-x M x P 1-y Si y O 4 (1),
where:
an average valence of Fe is +2 or more;
M is an element having a valence of +2 or more and is at least one type of element selected from a group consisting of Zr, Y, and Al;
the valence of M is different from the average valence of Fe;
0<x≦0.5; and 0<y<1, wherein:
a rate of chane in volume of a unit cell in Li x Fe 1-x M x P 1-y Si y O 4 is 4% or less with resect to a volume of a unit cell in General Formula (1).
2. The cathode active material according to claim 1 ,
wherein:
y=x ×({valence of M}− 2)+(1 −x )×({average valence of Fe}− 2).
3. The cathode active material according to claim 1 ,
wherein: the valence of M is +4.
4. The cathode active material according to claim 3 ,
wherein: M in General Formula (1) is Zr; and 0.15≦x≦0.5.
5. The cathode active material according to claim 3 ,
wherein: M in General Formula (1) is Zr; and 0.25≦x≦0.5.
6. The cathode active material according to claim 1 ,
wherein: the valence of M in General Formula (1) is +3.
7. The cathode active material according to claim 6 ,
wherein: M in General Formula (1) is Y; and 0.2≦x≦0.5.
8. The cathode active material according to claim 6 ,
wherein: M in General Formula (1) is Al; and 0.35≦x≦0.5.
9. The cathode active material according to claim 1 ,
wherein: the average valence of Fe in General Formula (1) is +2.
10. The cathode active material according to claim 9 ,
wherein: M in General Formula (1) is Zr; and 0.05≦x≦0.15.
11. A cathode comprising:
the cathode active material according to claim 1 ;
a conductive material; and
a binder.
12. A nonaqueous secondary battery, comprising:
the cathode according to claim 11 ;
an anode;
an electrolyte; and
a separator.
13. The nonaqueous secondary battery according to claim 12 ,
when the battery reached a voltage of not less than 3.9 V,
the cathode active material has a composition represented by General Formula (2) below,
Li x Fe 1-x M x P 1-y Si y O 4 (2).
14. The nonaqueous secondary battery according to claim 13 ,
wherein: the nonaqueous secondary battery is one of a laminate battery, a layered cuboidal battery, a wound cuboidal battery, and a wound cylindrical battery.
15. The nonaqueous secondary battery according to claim 13 ,
wherein: the nonaqueous secondary battery has an armor of the battery in the case where the armor is made of a metal.
16. A module comprising:
a combination of a plurality of the nonaqueous secondary battery according to claim 12 .
17. A power storage system comprising:
the nonaqueous secondary battery according to claim 12 .
18. The power storage system according to claim 17 ,
wherein: the power storage system is one of a power storage system for a solar battery, a storage system for late-night power, a power storage system for wind power generation, a power storage system for geothermal power generation, and a power storage system for wave activated power generation.