Nonaqueous secondary battery and method of using the same
A nonaqueous secondary battery containing a positive electrode having a positive electrode mixture layer, a negative electrode, and a nonaqueous electrolyte, wherein the positive electrode comprises, as active materials, two or more lithium-containing transition metal oxides having different average particle sizes, and the lithium-containing transition metal oxide having the smallest average particle size contains one or more of Mg, Ti, Zr, Ge, Nb, Al and Sn.
1. A nonaqueous secondary battery comprising:
a positive electrode having a positive electrode mixture layer, a negative electrode, and a nonaqueous electrolyte,
wherein the positive electrode comprises, as active materials, at least two lithium-containing transition metal oxides having different average particle sizes, and the lithium-containing transition metal oxide having the smallest average particle size is a lithium-containing transition metal oxide represented by the formula (1):
Li x M 1 y M 2 z M 3 v O 2 (1)
wherein M 1 represents at least one transition metal element selected from Co, Ni and Mn, M 2 represents Mg and at least one metal element selected from the group consisting of Ti, Zr, Ge, Nb, Al and Sn, M 3 represents at least one element selected from the group consisting of Na, K, Rb, Be, Ca, Sr, Ba, Sc, Y, La, Hf, V, Ta, Cr, Mo, W, Tc, Re, Fe, Ru, Rh, Cu, Ag, Au, B, Ca, In, Si, P and Bi, and x, y, z and v are numbers satisfying the equations respectively: 0.97≦x<1.02, 0.8≦y<1.02, 0.002≦z≦0.05, and 0≦v≦0.05, and has an average particle size from 2 μm to 10 μm, and the lithium-containing transition metal oxide having the largest average particle size is a lithium-containing transition metal oxide represented by the formula (2):
Li a M 1 b M 2 c M 3 d O 2 (2)
wherein M 1 , M 2 and M 3 are the same as defined in the formula (1), and a, b, c and d are numbers satisfying the equations respectively: 0.97≦a<1.02, 0.8≦b<1.02, 0.0002≦c≦0.02, and 0≦d≦0.02, and has an average particle size from 5 μm to 25 μm,
wherein said electrolyte contains a fluorine-containing organic solvent,
wherein the content of Co in the transition metal M 1 of the formulae (1) and (2) is from 30% by mole to 100% by mole,
wherein the content of said lithium-containing transition metal oxide having the smallest average particle size in the lithium-containing transition metal oxides is from 5% by weight to 60% by weight,
wherein the content of said lithium-containing transition metal oxide having the largest average particle size in the lithium-containing transition metal oxides is from 40% by weight to 95% by weight, and
wherein an amount of said fluorine-containing organic solvent is 0.1% by weight to 30% by weight based on the whole weight of the electrolyte.
2. The nonaqueous secondary battery according to claim 1 , wherein the lithium-containing transition metal oxide having the largest average particle size is a lithium-containing transition metal oxide represented by the formula (2) wherein c and d satisfy the following equation, respectively: 0.0002≦c<0.005 and 0≦d<0.005.
3. The nonaqueous secondary battery according to claim 2 , wherein z in the formula (1) is larger than c in the formula (2).
4. The nonaqueous secondary battery according to claim 1 , wherein z in the formula (1) is larger than c in the formula (2).
5. The nonaqueous secondary battery according to claim 1 , wherein, in the formula (1), the metal elements M 2 are Mg and at least one metal element selected from the group consisting of Ti, Zr, Ge, Nb, Al and Sn; a content of Mg is from 0.1% by mole to less than 2% by mole based on the amount of the transition metal M 1 ; when Ti, Zr, Ge or Nb is contained, a total content thereof is from 0.05% by mole to less than 0.5% by mole based on the amount of the transition metal M 1 ; and when Al or Sn is contained, a total content thereof is from 0.1% by mole to less than 1% by mole based on the amount of the transition metal M 1 .
6. The nonaqueous secondary battery according to claim 1 , wherein, in the formula (2), the metal elements M 2 are Mg and at least one metal element selected from the group consisting of Ti, Zr, Ge, Nb, Al and Sn; a content of Mg is from 0.01% by mole to less than 0.5% by mole based on the amount of the transition metal M 1 ; when Ti, Zr, Ge or Nb is contained, a total content thereof is from 0.005% by mole to less than 0.3% by mole based on the amount of the transition metal M 1 ; and when Al or Sn is contained, a total content thereof is from 0.01% by mole to less than 0.5% by mole based on the amount of the transition metal M 1 .
7. The nonaqueous secondary battery according to claim 1 , wherein said positive electrode mixture layer has a density of 3.5 to 4.6 g/cm 3 .
8. The nonaqueous secondary battery according to claim 1 , wherein said electrolyte further contains a fluorine-containing aromatic compound other than said fluorine-containing organic solvent.
9. The nonaqueous secondary battery according to claim 1 , wherein the fluorine-containing organic solvent is fluoroethylene carbonate.
10. The nonaqueous secondary battery according to claim 1 , wherein M 1 represents Co.
11. A method of using a nonaqueous secondary battery according to claim 1 comprising the step of:
charging the battery so that a positive electrode voltage is in a range of 4.35 to 4.6 V with reference to the potential of lithium when the battery is fully charged.