磷酸铁锂电池寿命初期与末期安全性差异

doi:10.11949/0438-1157.20221339

摘要/Abstract

摘要：

相比新鲜电池，锂离子电池在全生命周期内的安全性研究更值得关注。以寿命初期（BOL）与寿命末期（EOL）两种状态下的大尺寸方型铝壳磷酸铁锂动力电池为研究对象，先分析了BOL和EOL电池在比热容、热导率、材料热稳定性以及直流内阻方面的差异，再详细对比了电池在过放电、过充电、外部短路、加热、针刺、挤压等安全性能的差异。结果表明，相比BOL电池，EOL电池比热容由1.088 J/(g·℃)降低为1.065 J/(g·℃)；电池高度、宽度、厚度方向的热导率分别从25.84、21.21、1.05 W/(m·K)降低为22.20、18.44、1.00 W/(m·K)；负极材料和电解液的放热峰向低温偏移，121℃附近出现固体电解质界面膜分解放热峰，嵌锂石墨层间化合物、电解液和黏结剂间的反应放热焓由1019 J/g减小为841 J/g。安全性方面，EOL电池过放电产气更多，厚度鼓胀大；过充电产气更多，防爆阀提前7%荷电态开启；外部短路电流无法熔断转接片，电池将持续放电至过放态，产气鼓胀严重；针刺无烟雾释放、防爆阀未开启，安全性大幅提升，加热引发热失控的温度差别不大，其他安全测试项差异较小。研究结果丰富了锂离子电池全生命周期内安全性能的研究，有助于电池单体、模组及系统热失控防护设计。

关键词: 磷酸铁锂, 动力电池, 安全, 寿命初期, 寿命末期

Abstract:

Compared with fresh batteries, the safety research of lithium-ion batteries in the whole life cycle is more worthy of attention. The large-size prismatic aluminum-shell lithium iron phosphate power batteries in two states, i.e., beginning of life (BOL) and end of life (EOL) were selected as the research objects. The specific heat capacity, thermal conductivity, material's thermal stability and direct current internal resistance of BOL and EOL batteries were analyzed firstly. The safety differences of BOL and EOL batteries were compared in detail, such as over-discharge, over-charge, external short-circuit, heating, nail penetration, and crush, etc. The results show that compared to BOL battery, the specific heat capacity of the EOL battery decreases from 1.088 J/(g·℃) to 1.065 J/(g·℃). The thermal conductivity in the height, width, and thickness directions of the battery decreased from 25.84, 21.21, 1.05 W/(m·K) to 22.20, 18.44, 1.00 W/(m·K). The exothermic peaks shifted to low temperature, and the exothermic peak of solid electrolyte interface film decomposition appeared near 121℃, and the exothermic enthalpy of the reaction between the intercalated lithium-graphite compounds, electrolyte, and binder decreased from 1019 J/g to 841 J/g. In terms of safety, the EOL battery after over-discharge generated more gas, leading to a larger thickness swelling. Over-charge produced more gas with EOL battery, and the vent opened ahead of 7% state of charge. The external short-circuit current cannot fuse the connecting structure, and the battery would discharge continually to over-discharge state, giving more gas production and serious swelling. The nail penetration did not release smoke, the vent was not broke, and the safety was greatly improved. The temperature of thermal runaway caused by heating was close, and the differences of other safety test items were little. The research results enriched the research on the safety performance of lithium-ion batteries in the whole life cycle, and contributed to the thermal runaway protection design of batteries, modules and systems.

Key words: lithium iron phosphate, power battery, safety, beginning of life, end of life

中图分类号:

TM 912.9

刘伯峥, 王静波, 曾涛, 殷雅侠, 郭玉国. 磷酸铁锂电池寿命初期与末期安全性差异[J]. 化工学报, 2022, 73(12): 5555-5563.

Bozheng LIU, Jingbo WANG, Tao ZENG, Yaxia YIN, Yuguo GUO. Safety differences of LiFePO₄ batteries at the beginning of life and end of life[J]. CIESC Journal, 2022, 73(12): 5555-5563.

图/表 14

表1 寿命初期和寿命末期电池的热导率和比热容对比

Table 1 Themal conductivity and specific heat capacity contrast of BOL and EOL batteries

电池状态

热导率/(W/(m·K))

比热容/

(J/(g·℃))

图1 寿命初期和寿命末期电池拆解的活性材料与电解液DSC曲线

Fig.1 DSC curves of active materials and electrolyte disassembled from BOL and EOL batteries

图2 寿命初期和寿命末期电池的直流内阻及变化率

Fig.2 DCR and ΔDCR of BOL and EOL batteries

图3 寿命初期和末期电池过放电曲线

Fig.3 Overdischarge curve of BOL and EOL batteries

表2 寿命初期和末期电池过放电测试后的电压、内阻、质量及厚度变化

Table 2 Voltage， resistance， mass and thickness change of BOL and EOL batteries after overdischarge

电池状态	电压变化/mV	内阻变化/%	质量变化/g	厚度变化/%
BOL	-3345	+12.5	0	+6.6
EOL	-3346	+65.1	0	+28.0

图4 寿命初期和末期电池过充电曲线

Fig.4 Overcharge curve of BOL and EOL batteries

表3 寿命初期和末期电池过充电测试后的电压、内阻、质量及厚度变化

Table 3 Voltage， resistance， mass and thickness change of BOL and EOL batteries after overcharge

电池状态	电压变化/mV	内阻变化/%	质量变化/g	厚度变化/%
BOL	+100	+40.0	-11.0	+3.0
EOL	+19	+40.1	-46.0	+2.1

图5 寿命初期和末期电池外部短路曲线

Fig.5 External short circuit curve of BOL and EOL batteries

表4 寿命初期和末期电池过外部短路测试后的电压、内阻、质量及厚度变化

Table 4 Voltage， resistance， mass and thickness change of BOL and EOL batteries after external short circuit

电池状态	电压变化/mV	内阻变化/%	质量变化/g	厚度变化/%
BOL	-13	+2655	0	0.5
EOL	-2919	+30.4	0	21.1

图6 寿命初期和末期电池加热曲线T1,T4—加热箱温度;T2,T5—负极柱温度;T3,T6—负极侧壁温度

Fig.6 Heating curve of BOL and EOL batteries

表5 寿命初期和末期电池过加热测试后的电压、内阻、质量及厚度变化

Table 5 Voltage， resistance， mass and thickness change of BOL and EOL batteries after heating

电池状态	电压变化/mV	内阻变化/%	质量变化/g	厚度变化/%
BOL	-3350	+21.4	-588	+1.7
EOL	-3400	无	-568	+1.3

图7 寿命初期和末期电池针刺曲线

Fig.7 Nail penetration curve of BOL and EOL batteries

表6 电池寿命初期和末期针刺测试后的电压、内阻、质量及厚度对比

Table 6 Voltage， resistance， mass and thickness change of BOL and EOL batteries after nail penetration

电池状态	电压变化/mV	内阻变化/%	质量变化/g	厚度变化/%
BOL	-3353	945.6	-572	+6.5
EOL	-3326	78.6	-43.5	+2.8

图8 寿命初期和末期电池安全性变化

Fig.8 Safety performance changes of BOL and EOL batteries

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