锂离子电池正极材料低温性能衰退机理研究

Lithium-ion batteries have been widely used in portable devices, electric vehicles and large-scale energy storage due to their advantages of high specific capacity and long cycle life. However, the battery performance of lithium-ion batteries is closely related to the operating temperature. At lower operating temperatures, the energy and power density of lithium-ion batteries drop sharply, which severely limits the application of lithium-ion batteries in some cold regions. In order to explore the electrochemical performance degradation mechanism of the current commercial lithium-ion battery cathode materials under low temperatures, three commercial cathode materials, lithium iron phosphate(LiFePO₄), lithium cobalt oxide(LiCoO₂), and layered ternary oxide(LiNi_0.6Co_0.2Mn_0.2O₂) are selected as the research objects, and the electrochemical performance of these three materials at room temperature(25 ℃) and low temperature(−20 ℃) are compared via comprehensive characterization technologies including constant current charge and discharge test, electrochemistry impedance spectroscopy(EIS), galvanostatic intermittent titration technique(GITT) test, X-ray diffraction analysis(XRD) and scanning electron microscope(SEM). Constant current charge and discharge results show that the specific capacities of the three materials are significantly reduced at low temperatures. Among them, NCM622 delivers the optimal cycling stability, of which the capacity retention rate achieves 95.89% after 400 cycles when operating at −20 ℃. Alternating current impedance test analysis results further show that the increase of charge transfer resistance and the decrease of Li⁺ diffusivity at low temperature conditions are responsible for the degradation of the battery performance of lithium-ion battery cathode materials. This study provides a feasible method for improving the low-temperature performance of lithium-ion batteries.