富锂锰基正极材料在不同温度下的极化行为

Polarization behavior of lithium-rich manganese-based cathode materials at different temperatures

富锂锰基正极材料作为极具潜力的下一代锂离子动力电池正极材料,在不同温度下电化学性能表现出很大差异,严重限制了其在实际环境中的应用。采用多种电化学测试表征了富锂锰基材料在5~45℃温度范围内电化学性能的差异,从极化的角度分析了材料性能与温度依赖关系的影响因素。结果表明:富锂锰基材料的充放电容量随着温度的降低而降低,主要源于高电压和低电压区间内氧/锰离子反应随温度降低极化显著增大,造成其贡献的容量显著降低。这主要是因为氧/锰离子本征动力学性能差使电荷转移过程具有较高的表观活化能。此外,氧/锰离子参与电荷补偿反应使材料结构发生较大变化,一方面诱发界面膜成分发生变化,增加了低电压区间界面锂离子传输表观活化能,另一方面造成充放电末期锂离子固相扩散具有较高的表观活化能。因此,改善富锂锰基材料氧/锰离子反应动力学是提高其环境适应性的主要措施。

Lithium-rich manganese-based cathode material is a promising next-generation lithium-ion battery cathode material,however,it exhibits significant differences in electrochemical performance at different temperatures,which severely limits the application in practical environments.A variety of electrochemical measures were used to characterize the difference in electrochemical performance of lithium-rich material within the temperature range of 5-45℃.The influencing factors of material properties and temperature dependence were analyzed from the perspective of polarization.The results show that the charge/discharge capacity of lithium-rich material decreases with decreasing temperature,which is mainly due to the significant increase in the polarization of the oxygen/manganese ion reaction in the high-voltage and low-voltage ranges with decreasing temperature,resulting in a severe decrease in its capacity contribution.The significantly increased polarization is mainly caused by the poor intrinsic kinetic performance of oxygen/manganese ions,which leading to high apparent activation energy of the charge transfer process.In addition,the participation of oxygen and manganese ions in the charge compensation reaction changes the structure of the material seriously.It induces changes in the composition of the interface film,which increases the apparent activation energy of lithium ion transmission at the interface in the low voltage interval.Moreover,it causes bulk diffusion of lithium ions at the end of the charge and discharge process having higher apparent activation energy.Therefore,improving the oxygen/manganese ion reaction kinetics of lithium-rich material is the main method to enhance its environmental adaptability.