Cathode active material and lithium secondary battery containing the same
View Patent ↗Provided is a non-aqueous electrolyte-based, high-power lithium secondary battery having a long service life and superior safety at both room temperature and high temperature, even after repeated high-current charging and discharging. The battery comprises a cathode active material composed of a mixture of lithium/manganese spinel oxide and lithium/nickel/cobalt/manganese composite oxide wherein the cathode active material exhibits the life characteristics that the capacity at 300 cycles is more than 70% relative to the initial capacity, in the provision of satisfying the condition (i) regarding the particle size and the condition (ii) regarding the mixing ratio.
1. A cathode active material for a lithium secondary battery, comprising a mixture of a lithium/manganese spinel oxide represented by Formula I and a lithium/nickel/cobalt/manganese composite oxide represented by Formula II, wherein the cathode active material exhibits the life characteristics that the capacity at 300 cycles is more than 80% relative to the initial capacity, in the provision that the below conditions (i) and (ii) are satisfied,
(i) the lithium/manganese spinel oxide of Formula I has an average particle diameter of 15-30 μm, or the lithium/manganese spinel oxide of Formula I and the lithium/nickel/cobalt/manganese composite oxide of Formula II have an average particle diameter of 15-30 μm, respectively; and
(ii) the mixing ratio of the lithium/manganese spinel oxide:lithium/nickel/cobalt/manganese composite oxide is in the range of 10:90 to 70:30 (w/w),
Li 1+x Mn 2 O 4 (I)
Li 1+y Ni b Mn c Co 1−(b+c) O 2 (II)
wherein,
0≦x≦0.2;
0≦y≦0.1;
0.2≦b≦0.7;
0.2≦c≦0.7; and
b+c<1;
wherein each oxide is an aggregate of large numbers of oxide units, and
wherein an oxide unit of the lithium/manganese spinel oxide of Formula I has a particle diameter of 0.2 to 12 μm and surface area of 0.1 to 1.0 m 2 /g.
2. The cathode active material according to claim 1 , wherein the lithium/nickel/cobalt/manganese composite oxide of Formula II is Li 1+z Ni 1/3 Co 1/3 Mn 1/3 O 2 .
3. The cathode active material according to claim 1 , wherein the lithium/nickel/cobalt/manganese composite oxide of Formula II is Li 1+z Ni 0.4 Mn 0.4 Co 0.2 O 2 .
4. The cathode active material according to claim 1 , wherein the lithium/manganese spinel oxide is a lithium/manganese spinel oxide of Formula III wherein a portion of manganese (Mn) is substituted with other metal elements:
Li 1+x Mn 2−z M z O 4 (III)
wherein,
M is a metal having an oxidation number of 2 or 3;
0≦x≦0.2; and
0<z≦0.2.
5. The cathode active material according to claim 4 , wherein M in Formula III is aluminum (Al), magnesium (Mg) or both of them.
6. The cathode active material according to claim 4 , wherein the value of z is in the range of 0.01 to 0.2.
7. A lithium secondary battery comprising a cathode active material of claim 1 .