Low-temperature characteristics of cathode materials for lithium-ion batteries

The low-temperature characteristic layered structure of the layered structure cathode material not only has the incomparable rate performance of the one-dimensional lithium ion diffusion channel, but also has the structural stability of the three-dimensional channel. It is the earliest commercial lithium ion battery cathode material. Its representative materials are LiCoO2, Li(Co1-xNix)O2 and Li(Ni,Co,Mn)O2 and so on. Xie Xiaohua and others took LiCoO2/MCMB as the research object and tested its low-temperature charge and discharge characteristics. The results showed that with the decrease of temperature, its discharge platform dropped from 3.762V (0℃) to 3.207V (-30℃); its total battery capacity also dropped sharply from 78.98mA·h (0℃) to 68.55mA·h (–30°C). 2 The low-temperature characteristics of the spinel structure cathode material The spinel structure LiMn2O4 cathode material does not contain Co element, so it has the advantages of low cost and non-toxicity. However, the variable valence of Mn and the Jahn-Teller effect of Mn3+ lead to the structural instability and poor reversibility of this component. Peng Zhengshun et al. pointed out that different preparation methods have a greater impact on the electrochemical performance of LiMn2O4 cathode materials. Take Rct as an example: the Rct of LiMn2O4 synthesized by high-temperature solid-phase method is significantly higher than that synthesized by sol-gel method, and this phenomenon is caused by lithium ion. The diffusion coefficient is also reflected. The reason is mainly due to the greater influence of different synthesis methods on the crystallinity and morphology of the product. 3 Low-temperature characteristics of phosphate system cathode materials LiFePO4 has become the main body of current power battery cathode materials due to its excellent volume stability and safety, together with ternary materials. The poor low-temperature performance of lithium iron phosphate is mainly due to the material itself is an insulator, low electronic conductivity, poor lithium ion diffusivity, and poor conductivity at low temperatures, which increases the internal resistance of the battery, greatly affected by polarization, and hinders the charging and discharging of the battery, so the low temperature Performance is not ideal. When studying the charging and discharging behavior of LiFePO4 at low temperature, Gu Yijie et al. found that the coulombic efficiency dropped from 100% at 55℃ to 96% at 0℃ and 64% at -20℃; the discharge voltage dropped from 3.11V at 55℃. Decrease to 2.62V at -20℃. Xing et al. used nano-carbon to modify LiFePO4, and found that after adding nano-carbon conductive agent, the electrochemical performance of LiFePO4 is less sensitive to temperature, and the low-temperature performance is improved; after modification, the discharge voltage of LiFePO4 is 3.40 at 25°C. When V drops to 3.09V at -25℃, the reduction is only 9.12%; and its battery efficiency at -25℃ is 57.3%, which is higher than 53.4% u200bu200bwithout nano-carbon conductive agent. Recently, LiMnPO4 has aroused great interest. The study found that LiMnPO4 has the advantages of high potential (4.1V), no pollution, low price, and large specific capacity (170mAh/g). However, due to the lower ion conductivity of LiMnPO4 than LiFePO4, in practice, Fe is often used to partially replace Mn to form LiMn0.8Fe0.2PO4 solid solution. The low-temperature characteristics of lithium-ion battery anode materials are more serious than cathode materials. The low-temperature deterioration of lithium-ion battery anode materials is more serious, mainly due to the following three reasons: battery polarization is serious during low-temperature high-rate charging and discharging, and lithium metal on the negative electrode surface A large amount of deposition, and the reaction product of lithium metal and electrolyte is generally not conductive; from the perspective of thermodynamics, the electrolyte contains a large number of polar groups such as C–O and C–N, which can react with the negative electrode material to form the SEI The film is more susceptible to low temperature; the carbon negative electrode has difficulty in inserting lithium at low temperature, and there is asymmetric charge and discharge.