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Research status of high-pressure lithium cobalt oxide materials

At present, the most widely studied and widely used high-voltage cathode material is lithium cobalt oxide, which has a two-dimensional layer. The structure, α-NaFeO2 type, is more suitable for the insertion and expulsion of lithium ions. The theoretical energy density of lithium cobalt oxide is 274mAh/g, which has the advantages of simple production process and stable electrochemical properties, so it has a high market share. In practical applications, only some lithium ions can be reversibly embedded and expelled in lithium cobalt oxide materials, and its actual energy density is about 167mAh/g (working voltage is 4.35V). Increasing the operating voltage can significantly increase its energy density, for example, increasing the operating voltage from 4.2V to 4.35V can increase the energy density by about 16%. However, under high voltage, lithium ions are embedded and detached from the material many times, which will cause the structure of lithium cobalt oxide to change from trigonal crystal system to monoclinic crystal system, and the lithium cobalt oxide material no longer has the ability to embed and excrete lithium ions, and the particles of the cathode material will loosen and fall off from the current collector, resulting in the internal resistance of the battery becoming larger and the electrochemical performance worsening.

At present, the modification of lithium cobalt oxide cathode materials is important to improve the crystal structure stability and interface stability of the materials from two aspects: doping and coating.

At present, lithium cobalt oxide high-voltage materials have been used in batches in high-energy-density batteries, such as high-end mobile phone battery manufacturers have higher and higher requirements for battery performance, which is important in the higher requirements for energy density, such as the energy density of 4.35V mobile phone batteries with carbon as the negative electrode is required to be about 660Wh/L, and the 4.4V mobile phone battery has reached about 740Wh/L, which requires the cathode material to have a higher compaction density and higher air volume. As well as better stability of the material structure under high compaction and high voltage. However, lithium cobalt oxide electrode materials have shortcomings such as lack of cobalt resources and high price, and cobalt ions have certain toxicity, which limit their wide application in power lithium batteries.