Application of reaction engineering approach in modelling vacuum baking of lithium battery

doi:10.11949/0438-1157.20220141

Abstract

Abstract:

Vacuum baking before electrolyte injection has an important impact on the cycling performance, safety and stability of lithium battery. Differences in cell structure design, material system, oven size, etc. will lead to differences in the vacuum drying process. For vacuum baking, drying performance varies with different cell design, materials and oven size. Reaction engineering approach (REA) to drying modelling has been widely used for convective drying under atmospheric pressure and high initial water content materials. Here, REA was applied to the extremely low moisture process for battery vacuum baking. The results matched well with the experimental results. The influence of environmental humidity on drying process is considered in this work, and the prediction error is less than 10%. The rules of thumb established in this work by single factor experiment can guide the improvement of vacuum drying process of lithium-ion battery. The application in mass production is also briefly introduced here. The current work has demonstrated that REA can have excellent application in vacuum drying for lithium battery.

Key words: lithium battery, vacuum, baking, reaction engineering approach, evaporation, simulation

摘要：

锂离子电池注液之前的真空干燥，对于电芯的循环性能、安全性、稳定性有极其重要的影响。电芯结构设计、材料体系、烘箱尺寸等的不同会导致真空干燥过程存在差异。反应工程方法(REA)在常压、高初始水含量的对流干燥模拟预测上已有广泛应用，本研究将REA干燥理论应用于真空、低初始水含量的干燥过程仿真，发现与实验结果匹配良好。同时考虑了电芯气袋与烘箱环境湿度变化对干燥过程的影响，水含量预测偏差小于10%，利用单因子仿真实验所总结的规律能用于指导锂电池真空干燥工艺的改善。介绍了该模型在生产中的应用情况，也表明REA将在锂电池真空干燥预测上有很好的工业应用前景。

关键词: 锂电池, 真空, 干燥, 反应工程方法, 蒸发, 模拟

CLC Number:

TQ 02

Xingfu YANG, Wen CHEN, Jie XIAO, Xiaodong CHEN. Application of reaction engineering approach in modelling vacuum baking of lithium battery[J]. CIESC Journal, 2022, 73(7): 3262-3272.

杨兴富, 陈文, 肖杰, 陈晓东. 反应工程方法在锂电池真空干燥模拟上的应用[J]. 化工学报, 2022, 73(7): 3262-3272.

Figures/Tables 22

Fig.1 Simplified model of vacuum drying

Fig.2 Simplified temperature (a) and environment pressure logarithm (b) curve

Table 1 Experimental conditions of vacuum drying

组别	温度/℃	真空度/kPa
1	85	-97
2	95	-97
3	85	-101
4	95	-101

Fig.3 Comparison of the simulated drying curve and experiment data

Fig.4 Comparison of the average vapor pressure in the cell under different conditions

Fig.5 Moisture contour of solid and gas phase (Group1：85℃ & -97 kPa)

Table 2 Deviation analysis

项目	组1	组2	组3	组4
相关系数平方R²	0.99909	0.99950	0.99889	0.99893
均方根误差RMSE	9.99408	10.69929	13.09409	9.70212
平均相对误差MRE	0.04018	0.07066	0.08872	0.07039

Table 3 Initial value of characteristic variable

变量	数值	数据来源
换气	有/无	实验
传质系数	$h m = D g δ × θ$	文献[13]
多孔介质平均直径	15 μm	实验
孔隙率	0.3	实验
初始水含量	700 mg/kg	实验

Table 3 Initial value of characteristic variable

变量	数值	数据来源
换气	有/无	实验
传质系数	$h m = D g δ × θ$	文献[13]
多孔介质平均直径	15 μm	实验
孔隙率	0.3	实验
初始水含量	700 mg/kg	实验

Fig.6 Effect of breathing action on drying process

Fig.7 Effect of breathing action on vapor pressure in the cell

Fig.8 Effect of mass transfer coefficient on drying process

Fig.9 Effect of average diameter of porous media on drying process

Fig.10 Effect of porosity of porous media on drying process

Fig.11 Effect of battery initial moisture on drying process

Fig.12 Comparison of drying simulation results between 0-D model and 3-D model

Fig.13 Temperature (a) and environment pressure logarithm (b) curve

Table 4 Equilibrium moisture content（dry basis） of lithium cobalt oxide battery

温度/℃	平衡干基含水率X_b
20	0.000300
75	0.000105
85	0.000086
95	0.000080
105	0.000070

Fig.14 Relative activation energy curve of lithium cobalt oxide battery

Fig.15 Comparison of moisture content prediction and experimental result of lithium cobalt oxide battery

Table 5 Comparison of measured and predicted moisture content under different experimental conditions

实验条件	实测水含量/ (mg/kg)	预测水含量/ (mg/kg)	偏差/ (mg/kg)
85℃&干燥200 min	73.4	79.9	6.5
85℃&干燥150 min	88.0	85.4	-2.6
85℃&干燥90 min	99.9	108.5	8.6
82℃&干燥90 min	119.5	116.1	-3.4
80℃&干燥85 min	129.7	132.7	3.0
85℃&干燥65 min	143.8	146.7	2.9
83℃&干燥65 min	158.3	164.5	6.2
83℃&干燥60 min	165.9	185.5	19.6

Fig.16 Comparison of measured and predicted moisture content in mass production

Fig.17 Comparison of moisture content prediction and experimental result of lithium iron phosphate (a) and ternary lithium battery (b)

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