锂离子电池正极材料低温性能衰退机理研究

Study on the Cathode Materials’Deterioration Mechanism for Lithium-ion Batteries at Low Temperature

锂离子电池凭借其高能量密度、长循环寿命等突出优势被广泛应用于便携式设备、电动汽车以及大规模储能领域。然而,锂离子电池对外界温度敏感,尤其是在较低的工作温度下,能量密度和功率密度急剧下降,这严重限制了其在寒冷地区的应用。为探究锂离子电池在低温环境下的性能衰减机理,选择磷酸铁锂(LiFePO_(4))、钴酸锂(LiCoO_(2))、层状三元(LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2))三种商业化正极材料作为研究对象,结合恒流充放电测试、电化学阻抗测试、恒电流间歇滴定技术以及X射线衍射分析和扫描电子显微镜表征技术,全面系统地比较了三种材料在室温(25℃)和低温(−20℃)下的电化学性能。恒流充放电测试结果显示三种正极材料在低温下均会出现比容量明显降低,三元NCM622表现出最佳的低温循环稳定性,在-20℃循环400圈时容量保持率为95.89%。进一步的交流阻抗测试分析和Li^(+)扩散速率计算表明,在低温条件下电解液电导率的降低、正极材料电荷转移阻抗的增加和Li^(+)扩散速率下降是导致锂离子电池正极材料低温性能退化的主要原因,该研究为提高锂离子电池的低温性能提供了可行的解决思路。

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(LiFePO_(4)),lithium cobalt oxide(LiCoO_(2)),and layered ternary oxide(LiNi_(0.6)Co_(0.2)Mn_(0.2)O_(2))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.