Field of the Invention
The present invention relates to a method of manufacturing a lithium nickel complex oxide, a lithium nickel complex oxide manufactured thereby, and a cathode active material including the lithium nickel complex oxide.
Description of the Related Art
Demand for secondary batteries as an energy source has been significantly increased as technology development and demand with respect to mobile devices have increased. Among these secondary batteries, lithium secondary batteries having high energy density, high operating potential, long cycle life, and low self-discharging rate have been commercialized and widely used.
Also, in line with growing concerns about environmental issues, a significant amount of research into electric vehicles and hybrid electric vehicles, which may replace vehicles using fossil fuels, such as gasoline vehicle and diesel vehicle, one of major causes of air pollution, has been conducted.
Nickel-metal hydride secondary batteries have been mainly used as power sources of the electric vehicles and hybrid electric vehicles. However, research into the use of lithium secondary batteries having high energy density and discharge voltage has been actively conducted and some of the research are in a commercialization stage.
Lithium-containing cobalt oxides are mainly used as cathode active materials of lithium secondary batteries, and in addition, the uses of lithium-containing manganese oxides having a layered crystal structure or a spinel crystal structure and lithium-containing nickel oxides are also in consideration.
The lithium-containing cobalt oxides among the above cathode active materials have been most widely used due to their excellent life characteristics and charge and discharge efficiency. However, since the lithium-containing cobalt oxides have low high-temperature stability and are relatively expensive materials due to the resource limit of cobalt used as a raw material, the lithium-containing cobalt oxides have disadvantages in that price competiveness is limited. The lithium-containing manganese oxides having a layered crystal structure or a spinel crystal structure have advantages in that thermal stability is excellent, they are inexpensive, and synthesis thereof is easy. However, the lithium-containing manganese oxides have limitations in that capacity is low, high-temperature characteristics are poor, and conductivity is low.
Also, the lithium nickel oxides are relatively inexpensive and exhibit battery characteristics such as high discharge capacity, but the lithium nickel oxides have limitations in that a rapid phase transition of a crystal structure may occur due to the volume changes accompanying charge and discharge cycles and stability may be rapidly reduced when exposed to air and humidity.
In order to address the above limitations, a significant amount of attempts and research into using lithium oxides, in which nickel-manganese and nickel-cobalt-manganese are respectively mixed at a ratio of 1:1 and 1:1:1, as a cathode active material has been conducted. A cathode active material prepared by mixing nickel, cobalt, or manganese has improved physical properties in comparison to cathode active materials prepared by separately using transition metals. However, simplification of a manufacturing process and improvement of rate capability still remain as issues that need to be addressed.
In particular, a lithium secondary battery including a typical cathode active material presents difficulties in its application to electric vehicles because it exhibits unstable life characteristics under high-voltage charge and discharge conditions for obtaining high capacity, and accordingly, the improvement thereof is required.