6LR61 battery.Three technologies improve the performance of lithium battery cathode materials

　　Increasing the voltage of lithium-ion battery cathode materials is a new idea to increase the energy density of lithium-ion batteries in recent years. High-voltage materials include two cathode materials with spinel-like crystal structure and olivine-like crystal structure. LiMPO4 (M=Co, Ni) is a typical high-voltage olivine-like crystal structure material. Among them, LiCoPO4 has a discharge potential of 4.8V, LiNiPO4 has a discharge potential of 5.2V, and the theoretical capacity is close to 170mAh/g.

　　5.2V is currently the highest charge and discharge voltage. Because an electrolyte that can match it has not yet been developed, there are no reports on the performance of LiNiPO4 cathode materials for lithium batteries. There are more reports on LiCoPO4 materials, but in the existing electrolyte system The cycle charge and discharge performance of the LiCoPO4 material obtained below is very poor.

　　The olivine-like crystal structure has three side effects under high voltage conditions: 1. The cathode material will react with the electrolyte to form a solid-liquid interface layer; 2. The electrolyte will partially dissolve Co ions, greatly deteriorating the cycle charge and discharge of lithium batteries. Performance; 3. Poor conductivity and low conductivity. Therefore, when using a high-voltage olivine-like crystal structure, necessary means must be implemented to improve its performance. There are three means.

　　1. Nanotechnology. The active material uses small nano-sized particles that have shorter lithium ion and electron transmission and diffusion paths than large micron-sized particles.

　　2. Doping. Unlike the spinel-like crystal structure, which can be doped with both cations and anions, the olivine-like crystal structure is only doped with cations to improve the conductivity of the cathode material.

　　3. Coating. Amorphous carbon coatings can form interconnected high-speed electron transmission channels to improve performance, especially first discharge capacity and charge-discharge cycle performance.

　　Generally speaking, LiMPO4 (M=Co, Ni) with an olivine-like crystal structure has more theoretical capacity than a spinel-like crystal structure, but due to low conductivity and poor cycle performance, this cathode material is used in lithium-ion batteries. There are not many R&D achievements in spinel-like crystal structure lithium-ion batteries, but entering the industrialization stage requires more advanced performance improvement technology, which mainly refers to power lithium batteries for electric vehicles.

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