Field
This disclosure relates to a positive active material, a positive electrode and a lithium battery including the positive active material, and a method of manufacturing the same.
Description of the Related Technology
With the advancement of small high tech devices such as digital cameras, mobile devices, notebook computers, and personal computers, demand for lithium secondary batteries, which are an energy source for the small high tech devices, has dramatically increased. Also, a stable lithium ion battery having high capacity is currently being developed for electric cars, which includes hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and electric vehicles (EV).
Various positive active materials have been investigated to develop a lithium battery that is suitable for the purpose described above.
As a positive active material for a lithium secondary battery, a single-component lithium cobalt oxide (LiCoO2) has been used; however, use of lithium composite metal oxide (Li(Ni—Co—Mn)O2, Li(Ni—Co—Al)O2, or the like) having a layer-structure and high capacity has been increasing. Also, a spinel-type lithium manganese oxide (LiMn2O4) and an olivine-type iron phosphate lithium oxide (LiFePO4) having high safety are receiving attention.
In particular, research is being conducted to increase the amount of nickel included in the lithium composite metal oxide to increase capacity of a battery.
However, as the amount of nickel included in the lithium composite metal oxide increases, an amount of Ni2+, which may substitute lithium site, increases, which facilitates the formation of NiO an impurity. NiO is highly reactive and thus, may react with an electrolyte and two or more NiOs may be connected to locally form a three dimensional structure preventing diffusion of lithium ions. As a result, structural stability of the battery degrades to decrease the capacity of the battery.
Accordingly, a method of improving charge and discharge efficiency and lifespan properties of a lithium battery by improving structural stability of a positive active material having high nickel content is needed.