Lithium-ion batteries demonstrate a noticeable volume swell before thermal runaway occurs. Therefore, studying the changing law of power battery swelling force is significant for improving battery performance and early warning safety. This study explores the changing law of the swelling force for ternary/graphite batteries when charging at various temperatures and rates. The increase in the swelling force of the power battery is minimum when charged at 25 ℃. Consequently, the low ambient temperature causes lithium ions to accumulate on the surface of the graphite layer, thereby increasing the battery thickness and swelling force. Moreover, the higher the ambient temperature, the larger the volume of the power battery; an SEI film is produced during charging, leading to a greater expansion force. When the power battery is charged at different rates, the swelling force gradually rises with an increase in charging rate, possibly because the high rate charging increases the battery temperature; the SEI film is formed on the material's surface. The CT scan results accurately quantify and analyze the thickness variations of the battery during the charging process. The capacity differential curve (dQ/dV) during the charging process reveals that the variation in the growth trend of the swelling battery force is primarily due to the various phase transitions of the positive and negative materials in the different charging stages. Then, the change characteristics of the expansion force in the charging process of the power battery are revealed from the mechanism level.
Keywords：lithium-ion battery
;
swelling force
;
phase transition
LIN Chunjing. Research on swelling force characteristics of power battery during charging[J]. Energy Storage Science and Technology, 2022, 11(5): 1627-1633
Fig. 2
Changing characteristics of swelling force of power battery: (a) Power battery charging capacity and swelling force curve at 0.05 C and different temperatures; (b) Power battery voltage, temperature, swelling force and swelling force change rate at 5 ℃ and 0.05 C as a function of charging capacity; (c) The voltage, temperature, swelling force and swelling force change rate of power battery at 25 ℃ and 0.05 C vary with the change of charging capacity; (d) The voltage, temperature, swelling force, and swelling force change rate of power battery at 45 ℃ and 0.05 C varies with the rate of change Change graph of charging capacity
Table 2
表2
表2动力电池在0.05 C、不同温度下膨胀力及其变化阶段对应的SOC数据表
Table 2 The SOC data table corresponding to the swelling force and the change stage of the power battery at 0.05 C and different temperatures
Fig. 3
When the power battery is charged at a rate of 0.05 C, 0.33 C, and 1 C at 25 ℃ (a) Charging capacity and swelling force curve; (b) Temperature change curve
Fig. 5
dQ/dV and voltage swelling force curve of power battery during charging at 25 ℃ and 0.05 C rate
容量微分曲线中的每个波峰反映了正负极材料的不同相变[18]，波峰对应的电压称为相变点。表3[19-22]列出了石墨负极不同锂化程度Li x C6对应的相及其对应的层间距，不同的层间距使得石墨负极的厚度不同，而动力电池充电过程中膨胀力的增加主要来自于负极厚度的增加。空电状态下石墨负极为2H相，随着充电过程的进行，逐渐发生相变，在波峰1处发生从1L→4L→3L的相变，此过程的石墨负极厚度增加较快，大约增加1.5%，进而导致膨胀力的快速增加。NCM正极材料在波峰2处较为稳定，收缩基本可忽略不计[19]；而石墨会发生3L→2L→2的相变，且相变过程由于石墨层间距增加较小，石墨负极厚度增加也较小，所以此时膨胀力增加缓慢。波峰3处的石墨负极相变为2→1，此相变过程石墨负极厚度增加较快，大约增加1.2%，则对应的膨胀力也快速增加。波峰4对应于NCM正极材料的相变，此时的正极材料具有明显的收缩；此外，此时的负极材料为LiC6，锂在石墨层的排布由杂乱状态转为有序状态，石墨负极厚度增加较小，正负极的综合作用使得膨胀力处于缓慢波动阶段[19]。
Table 3
表3
表3动力电池在25℃、0.05 C、0.33 C、1 C倍率充电时膨胀力数据表
Table 3 Swelling force data table of the power battery when charged at the rate of 0.05 C, 0.33 C, 1 C at 25 ℃
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... 容量微分曲线中的每个波峰反映了正负极材料的不同相变[18]，波峰对应的电压称为相变点.表3[19-22]列出了石墨负极不同锂化程度Li x C6对应的相及其对应的层间距，不同的层间距使得石墨负极的厚度不同，而动力电池充电过程中膨胀力的增加主要来自于负极厚度的增加.空电状态下石墨负极为2H相，随着充电过程的进行，逐渐发生相变，在波峰1处发生从1L→4L→3L的相变，此过程的石墨负极厚度增加较快，大约增加1.5%，进而导致膨胀力的快速增加.NCM正极材料在波峰2处较为稳定，收缩基本可忽略不计[19]；而石墨会发生3L→2L→2的相变，且相变过程由于石墨层间距增加较小，石墨负极厚度增加也较小，所以此时膨胀力增加缓慢.波峰3处的石墨负极相变为2→1，此相变过程石墨负极厚度增加较快，大约增加1.2%，则对应的膨胀力也快速增加.波峰4对应于NCM正极材料的相变，此时的正极材料具有明显的收缩；此外，此时的负极材料为LiC6，锂在石墨层的排布由杂乱状态转为有序状态，石墨负极厚度增加较小，正负极的综合作用使得膨胀力处于缓慢波动阶段[19]. ...
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... 容量微分曲线中的每个波峰反映了正负极材料的不同相变[18]，波峰对应的电压称为相变点.表3[19-22]列出了石墨负极不同锂化程度Li x C6对应的相及其对应的层间距，不同的层间距使得石墨负极的厚度不同，而动力电池充电过程中膨胀力的增加主要来自于负极厚度的增加.空电状态下石墨负极为2H相，随着充电过程的进行，逐渐发生相变，在波峰1处发生从1L→4L→3L的相变，此过程的石墨负极厚度增加较快，大约增加1.5%，进而导致膨胀力的快速增加.NCM正极材料在波峰2处较为稳定，收缩基本可忽略不计[19]；而石墨会发生3L→2L→2的相变，且相变过程由于石墨层间距增加较小，石墨负极厚度增加也较小，所以此时膨胀力增加缓慢.波峰3处的石墨负极相变为2→1，此相变过程石墨负极厚度增加较快，大约增加1.2%，则对应的膨胀力也快速增加.波峰4对应于NCM正极材料的相变，此时的正极材料具有明显的收缩；此外，此时的负极材料为LiC6，锂在石墨层的排布由杂乱状态转为有序状态，石墨负极厚度增加较小，正负极的综合作用使得膨胀力处于缓慢波动阶段[19]. ...
... 不同锂化程度的石墨层状化合物： X 是Li x C6 中的锂化程度， d 为参考文献中的层间距[19] ...
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... 容量微分曲线中的每个波峰反映了正负极材料的不同相变[18]，波峰对应的电压称为相变点.表3[19-22]列出了石墨负极不同锂化程度Li x C6对应的相及其对应的层间距，不同的层间距使得石墨负极的厚度不同，而动力电池充电过程中膨胀力的增加主要来自于负极厚度的增加.空电状态下石墨负极为2H相，随着充电过程的进行，逐渐发生相变，在波峰1处发生从1L→4L→3L的相变，此过程的石墨负极厚度增加较快，大约增加1.5%，进而导致膨胀力的快速增加.NCM正极材料在波峰2处较为稳定，收缩基本可忽略不计[19]；而石墨会发生3L→2L→2的相变，且相变过程由于石墨层间距增加较小，石墨负极厚度增加也较小，所以此时膨胀力增加缓慢.波峰3处的石墨负极相变为2→1，此相变过程石墨负极厚度增加较快，大约增加1.2%，则对应的膨胀力也快速增加.波峰4对应于NCM正极材料的相变，此时的正极材料具有明显的收缩；此外，此时的负极材料为LiC6，锂在石墨层的排布由杂乱状态转为有序状态，石墨负极厚度增加较小，正负极的综合作用使得膨胀力处于缓慢波动阶段[19]. ...
