Mg、Ti离子复合掺杂改性磷酸铁锂正极材料及其电池性能

在氮气气氛下采用高温固相方法, 合成了Mg、Ti 离子复合掺杂改性的锂离子电池正极材料(Li_0.98Mg_0.01)(Fe_0.98Ti_0.01)PO₄/C, 并通过粉末X射线衍射(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和充放电循环对材料进行性能表征. 测试结果表明, 复合离子掺杂可显著改善材料的电化学性能, 模拟电池在0.2C和1C倍率下的放电比容量分别为154.7 和146.9 mAh·g^-1. 以此复合掺杂样品为正极材料组装60 Ah动力电池, 其3C倍率放电容量仍保持为1C倍率放电容量的100%; 低温0 和-20 °C测试条件下, 动力电池放电容量分别保持为常温初始放电容量的89.7%和63.1%; 在常温1C/1C充放电条件下, 经过2000次循环后, 电池容量依然保持为初始放电容量的89%, 显示出优良的倍率放电性能和循环性能. 研究结果表明, Mg、Ti 离子复合掺杂改性的磷酸铁锂正极材料及其电池具有优良的放电性能和循环稳定性, 可广泛应用于电动(或混合动力)汽车和储能电池系统.     

Analysis on the capacity degradation mechanism of a series lithium-ion power battery pack based on inconsistency of capacity

The lithium-ion battery has been widely used as an energy source. Charge rate, discharge rate, and operating tem- perature are very important factors for the capacity degradations of power batteries and battery packs. Firstly, in this paper we make use of an accelerated life test and a statistical analysis method to establish the capacity accelerated degradation model under three constant stress parameters according to the degradation data, which are charge rate, discharge rate, and operating temperature, and then we propose a capacity degradation model according to the current residual capacity of a Li-ion cell under dynamic stress parameters. Secondly, we analyze the charge and discharge process of a series power battery pack and interpret the correlation between the capacity degradations of the battery pack and its charge/discharge rate. According to this cycling condition, we establish a capacity degradation model of a series power battery pack under inconsistent capacity of cells, and analyze the degradation mechanism with capacity variance and operating temperature difference. The comparative analysis of test results shows that the inconsistent operating temperatures of cells in the series power battery pack are the main cause of its degradation; when the difference between inconsistent temperatures is narrowed by 5 ℃, the cycle life can be improved by more than 50%. Therefore, it effectively improves the cycle life of the series battery pack to reasonably assemble the batteries according to their capacities and to narrow the differences in operating temperature among cells.