High lithium containing batteries are extensively used in modern life as electrochemical power sources.
There are two types of lithium batteries, namely primary lithium battery, and secondary battery. Lithium-ion secondary battery has been widely used in mobile phones, laptops and other modern appliances.
The cathode of a typical rechargeable lithium-ion battery uses a transition metal oxide material that can reversibly intercalate/deintercalate lithium at a high potential difference when carbon, for example, is used as the anode material. The first commercial lithium-ion batteries introduced in 1990 by Sony Corporation used LiCoO2 as the cathode material, which continues to be used in more than 90% of lithium-ion batteries. LiCoO2 has a well-ordered layered crystal structure, which is easily prepared and enables a fast and reversible lithium intercalation. However, LiCoO2 has poor thermal stability and is toxic, rendering it unsuitable for large-sized battery applications, such as electric and hybrid vehicles, that require batteries to be stable, economical and environmentally friendly, along with good performance.
To replace layer-structured LiCoO2, other cathode materials have been developed for many years. These other cathode materials can be divided into cathode materials having a spinel crystal structure and cathode materials having an olivine crystal structure. A typical cathode material with an olivine crystal structure, for example, LiFePO4, has high theoretical capacity of about 170 mAh/g, low cost and non toxicity. However, the electronic conductivity of this type of cathode materials is poor, limiting its use in high charge/discharge rate applications, for example, in hybrid vehicles. Many methods have been researched to improve the conductivity of olivine lithium-based cathode materials. For example, LiFePO4 particles have been coated with a thin carbon layer or doped with some metal cations, and nano-sized cathode particles have been synthesized. These methods have improved the electric conductivity.
Manganese oxides having a spinel crystal structure offer lower cost and lower toxicity compared to cobalt, and have been demonstrated to be safer when overcharged. The most readily prepared lithiated manganese oxide with a spinel crystal structure is LiMn2O4. LiMn2O4 includes three-dimensional channels, which allow for lithium diffusion. Lithiated manganese oxide has a high work voltage (around 4.2V), but a lower capacity than that of LiCoO2, and low stability due to J-T distortion during lithium intercalation/de-intercalation. To improve its performance, LiMn2O4 has been doped with transition metals such as Cr, Ni and Cu among which LiNi0.5Mn1.5O4 shows a higher work voltage (around 4.5˜4.7V), a large capacity (around 147 mAh/g) and a relatively good cycle performance below a relative high current density of around 147 mA/g. Many efforts have been made to further optimize the electrochemical performance of lithiated nickel manganese oxide at high current density by the synthesizing nano-sized particles of lithiated nickel manganese oxide to make lithium diffusion easier and by doping lithiated nickel manganese oxide with metal cations to improve its structural stability and enhance its conductivity. However, these improvements have not been that effective in rendering the structural stability and conductivity of LiNi0.5Mn1.5O4 suitable for hybrid vehicles.