锂离子电池用微米厚度超薄集流体Cu箔和Al箔疲劳强度及损伤行为

Fatigue Strength and Damage Behavior of Micron-Thick Ultrathin Current Collector Cu Foil and Al Foil for Lithium-Ion Battery

随着高性能、高能量密度锂离子电池的飞速发展,锂离子电池用集流体金属箔轻薄化已成为行业技术升级的一个重要方向,随着集流体厚度的减小,其疲劳失效问题变得日益突出。本工作通过拉-拉疲劳实验和EBSD技术研究了循环载荷作用下锂离子电池用集流体Cu箔和Al箔的高周疲劳强度及失效行为。结果表明,Cu箔疲劳裂纹主要萌生于较大晶粒内部的滑移带处,并沿滑移带扩展。基于对损伤晶粒微观结构的观察和统计分析,获得了Cu箔疲劳裂纹萌生和材料微观结构(晶粒尺寸及其变异系数、晶粒取向、Schmid因子(Ω))的统计关系图。Al箔由于表面含有轧制缺陷,其疲劳裂纹优先在表面加工缺陷处萌生。通过极值统计法成功预测了Al箔样品中可能的缺陷分布以及存在的最大缺陷尺寸,并基于Kitagawa-Takahashi图建立了缺陷尺寸与疲劳极限之间的关系。

With the rapid development of high-performance and high-energy-density lithium-ion batteries,lightweight current collector metal foils for lithium-ion batteries have become a crucial direction of industrial technological advancements.As the thickness of the current collector decreases,the fatigue failure problem becomes increasingly prominent.Once the fatigue failure of the current collector occurs,it will have a catastrophic impact on the electrochemical and safety performances of lithium-ion batteries.Here,to further clarify the fatigue damage mechanism of current collector foils,the high cycle fatigue strength and fatigue failure behavior of current collector Cu and Al foils for lithium-ion batteries under cyclic loading were experimentally investigated using tensile-tensile fatigue test and the EBSD technique.Results show that the fatigue cracks of the Cu foils mainly originate from the slip bands with larger grain sizes and propagate along the slip bands.Based on the microstructure observation and analysis of damaged grains,a statistical relationship between fatigue crack initiation and microstructure(grain size and its coefficient of variation,grain orientation,and Schmid factor(Ω))of the Cu foils was obtained.Due to the presence of rolled defects on the surface of Al foils,the fatigue cracks are preferentially initiated at the surface defects.Extreme value statistics accurately predicted the possible defect population and the largest defect size in the Al foils,and the relationship between the defect size and fatigue limit was established using the Kitagawa-Takahashi diagram.