1. Field
This disclosure relates to a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same.
2. Description of the Related Technology
Recently, research on rechargeable lithium batteries having high energy density for power source of portable electronic devices have been actively undertaken due to reductions in size and weight of portable electronic equipment, and popularization of portable electronic devices.
A rechargeable lithium battery is manufactured using materials for negative and positive electrodes that intercalate or deintercalate lithium ions, and filing an organic electrolyte solution or a polymer electrolyte that transfer lithium ions between the positive and negative electrodes.
A rechargeable lithium battery may use a lithium metal as a negative active material, but dendrite formation on the surface of the lithium metal during charge and discharge is possible and may cause a battery short circuit and battery destruction. In order to solve this problem, a carbon-based material reversibly receiving and supplying lithium ions as well as maintaining a structure and electric property and having a similar half-cell potential to a lithium metal during intercalation/deintercalation of lithium ions has been widely used as a negative active material.
For a positive active material of a rechargeable lithium battery, metal chalcogenide compounds being capable of intercalating and deintercalating lithium ions, and for example, composite metal oxide such as LiCoO2, LiMn2O4, LiNiO2, LiNi1−xCoxO2 (0<x<1), LiMnO2, and the like has been used. LiNiO2 among the positive active materials has high charge capacity but is difficult to synthesize, while a Mn-based active material such as LiMn2O4, LiMnO2, and the like is easy to synthesize, and relatively inexpensive but have relatively small capacity. In addition, the LiCoO2 shows electrical conductivity of about 10−2 S/cm to 1 S/cm at room temperature, high battery voltage, and excellent electrode characteristics and thus, has been widely used but has low stability during high-rate charge and discharge.
In general, these composite metal oxides are prepared in a solid-phase reaction method of mixing raw powders in a solid state and firing the mixture. For example, LiNi1−xCoxO2 (0<x<1) may be prepared by mixing Ni(OH)2 with Co(OH)2 or hydroxide containing Ni and Co, then, heat-treating, pulverizing, and filtering LiNi1−xCoxO2 (0<x<1) using sieves, and the like. Another method of preparing composite metal oxides includes forming a crystalline active material by reacting LiOH, Ni oxide, and Co oxide, primarily sintering the reactant to form an initial oxide at 400° C. to 580° C., and secondarily sintering the initial oxide at 600° C. to 780° C.
When active materials prepared using the above methods are used to manufacture a rechargeable lithium battery, the active materials may not maintain main characteristics of the rechargeable lithium battery at a high voltage due to a side reaction with an electrolyte and the like.