Positive-electrode active material for nonaqueous-electrolyte secondary battery, and positive electrode and secondary battery using said positive-electrode active material
Provided are a cathode active material that has improved crystal-structure stability during continuous or high-voltage charging of a nonaqueous electrolyte rechargeable material, excellent cycle characteristics (capacity retention), and high capacity, as well as a cathode and a nonaqueous electrolyte rechargeable battery containing the cathode active material. The cathode active material has a composition represented by formula (1): Li x−y Na y Co w Al a Mg b M c O 2+α wherein x, y, w, a, b, c, and α each denotes particular values; and M stands for at least one element selected from Ca, Y, rare earth elements, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Ni, Cu, Ag, Zn, B, Ga, C, Si, Sn, N, P, S, F, and Cl; wherein the cathode active material is in the form of lithium-containing composite oxide particles having a compound adhered on a surface thereof, the compound containing at least one element selected from Al, Mg, and M.
1. A cathode active material for a nonaqueous electrolyte rechargeable battery, comprising a lithium-containing composite oxide particle and a compound adhered on a surface thereof,
wherein said cathode active material has a composition of formula (1):
Li x−y Na y Co w Al a Mg b M c O 2+α (1)
wherein x, y, w, a, b, c, and a fulfill 1.005<(x−y)<1.041, 0.009≤y≤0.020, 1.010<x≤1.050, 0.990≤w≤1.015, 0.005≤a≤0.020, 0.001≤b≤0.020, 0.001≤c≤0.003, −0.1≤α≤0.1; and M consists of Ti and Zr; and
wherein said compound contains at least one element selected from the group consisting of Al, Mg, and M.
2. The cathode active material for a nonaqueous electrolyte rechargeable battery according to claim 1 , wherein y fulfills 0.009≤y≤0.018.
3. The cathode active material for a nonaqueous electrolyte rechargeable battery according to claim 1 , wherein a ratio (x)/(w+a+b+c) of (Li+Na) to (Co+Al+Mg+M) is not less than 0.990 and not more than 1.020.
4. A cathode for a nonaqueous electrolyte rechargeable battery comprising the cathode active material for a nonaqueous electrolyte rechargeable battery of claim 1 .
5. A nonaqueous electrolyte rechargeable battery comprising the cathode for a nonaqueous electrolyte rechargeable battery of claim 4 .