Figure 1 lists the characteristics, capacity, density, shape of the charge-discharge curve, and problems with cathode materials for lithium-ion batteries. Since the invention of lithium-ion batteries, LiCoO2 has occupied more than 90% of the market share of cathode materials for lithium-ion batteries, mainly used in mobile phones and notebook computers, and manganese-based materials occupy the remaining market share.
For batteries, the most important thing is how to increase the amount of active material per unit volume, so volumetric capacity is a key factor. Cobalt-based material is a promising cathode material due to its high density and volume specific capacity of 808 mA h. In addition, the discharge curve of the battery is also important because it is easier to design the protection circuit of the battery because the slope of the curve is large.
The capacity of Li-ion batteries was initially increased by improving the carbon anode, however, the increase in capacity can now also be achieved by increasing the charging voltage of the battery. By doping LiCoO2 with other ions, it is possible to achieve higher charging voltages for Li-ion batteries without fading in capacity. For the 18650-type battery, by doping the cathode material LiCoO2 with elements such as magnesium or aluminum, a capacity as high as 2.4 A·h can be obtained.
For safety reasons, the practical application of nickel-based materials in high volume specific capacity lithium-ion batteries has been postponed. However, the safety of LiNiO2 batteries doped with different metals has been verified, and batteries using nickel-based cathode materials have actually been used in 2004. annual production.
At the same time, spinel-like lithium manganate materials also show good safety performance, and are considered to be a kind of potential in the application fields of large batteries such as hybrid electric vehicles (HEV) and pure electric vehicles (EV). alternative material. As long as ten batteries with a capacity of 10A • h are connected in series, a HEV battery module can be formed. Lightweight laminated cells are suitable for these applications, and the price of the cells will be lower. In 2002, as a power source for electric motorcycles and power-assisted bicycles, a manganese-based material laminated battery has been put into the market. In 2003, the battery became the power source for hybrid vehicles. The capacity fading problem of manganese-based cathode materials at high temperatures has been overcome, and it is safe to say that such batteries will use manganese-based materials. Spinel doped with aluminum and magnesium is also widely used because it is not easy to form oxygen-deficient compounds.