Comparison and analysis of performance of cathode materials for lithium ion batteries
Common cathode materials include lithium cobalt oxide, lithium manganate, lithium iron phosphate, and ternary materials.
1. Lithium Cobalt Oxide (LiCoO2)
Lithium cobaltate is the first commercially available cathode material for lithium-ion batteries. It has a layered structure with a theoretical specific capacity of 274mAhg-1. However, in the actual charging and discharging process, in order to maintain the stability of the structure, only part of the lithium ions can be inserted and removed, so the actual capacity is only 130-140mAhg-1. At the same time, due to the relatively poor resources of cobalt, the high price, and the toxicity to the environment, coupled with the poor safety performance of the material and the relatively low capacity, its wide application and long-term development are greatly restricted. At present, lithium cobalt oxide material batteries are mainly used in digital batteries.
2. Lithium manganate
Lithium manganate has spinel type and layered type, the most important being spinel type lithium manganate. Compared with lithium cobalt oxide, it has the characteristics of abundant resources, low price, low environmental pollution and excellent safety performance. The theoretical capacity of LiMn2O4 with spinel structure is about 148mAhg-1. In practical applications, the capacity is 90-120mAhg-1, and the normal working voltage is 3-4V. However, within the charging and discharging range of 3V, the reversibility of Li+ insertion and extraction reactions is poor. It is difficult to maintain the integrity of the spinel structure, and the cycleability is poor. In high temperature cycles, the dissolution of manganese in the electrolyte and the Jahn-Teller effect also cause serious capacity degradation of the material.
3. Lithium iron phosphate
LiFePO4 has a typical olivine structure, the theoretical specific capacity is about 170mAhg-1, and it reaches 150mAhg-1 in practical applications. Lithium iron phosphate is rich in raw materials, relatively inexpensive compared to other materials, and is environmentally friendly, coupled with better cycle performance and high safety, making it the first to be used in electric vehicles. However, the conductivity of lithium iron phosphate materials is poor, and the tap density is low, resulting in a low volume energy density, which limits its further application.
4. Ternary materials
Inspired by the doping modification of metal elements of lithium cobalt oxide, the multi-element metal composite oxide—the ternary material LiNi1-x-yCoxNyO2 (N=Mn, Al) has developed rapidly. The ternary material combines the advantages of lithium cobaltate, lithium nickelate and lithium manganate (lithium aluminate) to form a ternary co-solution, which can give full play to the use of the three components. Its theoretical capacity is relatively high, with a relatively balanced nature, and occupies an important position in the power battery market.
At present, the domestic lithium cobalt oxide technology is relatively complete and is mainly used in the field of consumer batteries. However, due to the scarcity of cobalt resources and its toxicity, it is being replaced by higher voltage lithium cobalt oxide, ternary materials with more balanced energy density and cost.
With the steady rise of consumer batteries and the rapid rise of power batteries, the output of cathode materials has gradually expanded.
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