Cathode material for use in lithium secondary battery and manufacturing method thereof
A cathode material for use in a lithium secondary battery of excellent thermal stability contributing to the improvement of safety of the battery and having large discharging capacity, as well as a method of manufacturing the cathode material for use in the lithium secondary battery, based on the improved method for measuring the thermal stability of the cathode material, the cathode material comprising a compound represented by the chemical formula: Li x Ni y Co z M m O 2 in which the material is powdery and the BET specific surface area is 0.8 m 2 /g or less, M in the chemical formula represents one or more of element selected from Ba, Sr and B, and x, y, z and m are, respectively, 0.9≦x≦1.1, 0.5≦y≦0.95, 0.05≦z≦0.5 and 0.0005≦m≦0.02.
1. A cathode material for use in a lithium secondary battery comprising a compound represented by the chemical formula: Li x Ni y Co z M m O 2 when not in a charged state, having high thermal stability and large discharging capacity in which M is selected from the group consisting of Ba and Ba with Sr, and x, y, z and m are values for the molar ratio of each element: 0.9≦x≦1.1, 0.5≦y≦0.95, 0.05≦z≦0.5 and 0.0005≦m≦0.005, wherein the compound represented by the chemical formula: Li x Ni y Co z M m O 2 when not in a charged state changes to a compound when in a charged state represented by the chemical formula: Li a Ni b Co c M n O 2 and a, b, c and n are values for the molar ratio of each element and are, respectively, 0.2≦a≦0.4, 0.5≦b≦0.95, 0.05≦c≦0.5, and 0.0005≦n≦0.005 and the material is powdery, has a BET specific surface area 0.8 m 2 /g or less and has a DTG increase start temperature at 215° C. or higher.
2. The cathode material defined in claim 1 , wherein the BET specific surface area is less than 0.5 m 2 /g.
3. The cathode material defined in claim 1 , wherein the compound represented by the chemical formula: Li x Ni y Co z M m O 2 has a tap density of 1.5 g/cm 3 or more.
4. A lithium secondary battery containing the cathode material defined in claim 1 .
5. A method of manufacturing a cathode material comprising a powdery compound represented by the chemical formula: Li x Ni y Co z M m O 2 , which M is Ba or Ba with Sr, and x, y, z and m are values for the molar ratio of each element: 0.9≦x≦1.1, 0.5≦y≦0.95, 0.05≦z≦0.5 and 0.0005≦m≦0.02, having a BET specific surface area 0.8 m 2 /g or less, comprising:
mixing only by a dry mixing process a powder of a compound represented by Ni y Co z (OH) 2 having a tap density 1.8 g/cm 3 or more and an average particle diameter of 5 to 20 μm, a lithium salt and a salt containing the element M to form a dry mixture, and
forming the cathode material by heating and pulverizing the diy mixture.
6. The method defined in claim 5 , wherein powdery particles of the compound represented by Ni y Co z (OH) 2 have a spherical shape.
7. The method defined in claim 5 , wherein heating includes conducting successively preliminary heating at 300 to 500° C. for 2 to 6 hrs in an oxygen atmosphere, a temperature elevation process of elevating the temperature at a rate of 5 to 30C/min after the preliminary heating and final heating at 650 to 900° C. for 2 to 30 hrs succeeding temperature elevation.
8. A cathode material for use in a lithium secondary battery comprising a compound represented by the chemical formula: Li x Ni y Co z M m O 2 having high thermal stability and large discharging capacity in which M is Ba or Ba with Sr, and x, y, z and m are values for the molar ratio of each element0.9≦x≦1.1, 0.5≦y≦0.95, 0.05≦z≦0.5 and 0.0005≦m≦0.005, wherein the material is powdery, has a BET specific surface area 0.8 m 2 /g or less, and has a DTG increase start temperature of 230° C. or higher in a charged state.
9. The cathode material defined in claim 8 , wherein the BET specific surface area is less than 0.5 m 2 /g.
10. The cathode material defined in claim 8 , wherein the compound represented by the chemical formula: Li x Ni y Co z M m O 2 has a tap density of 1.5 g/cm 3 or more.
11. A lithium secondary battery containing the cathode material defined in claim 8 .