The silicon-graphite composite electrode is the main focus of the high energy and high power density 18650 Li-ion battery cells, while the large volume expansion of the composite electrode may induce the steel case of the cell to deform largely, even rupture. The mechanical reliability of the steel case is very important to the safety and durability of the battery cell. In the paper, the hoop strain of the steel case is in-situ monitored during 18650 Li-ion battery cell operation. At the early cycle stage, the hoop strain of the steel case is induced by the thermal expansion. After a long-term cycle (cycled number > 300 times), inhomogeneous strain distribution, even negative strain, is found on the steel case. Based on the CT images and non-concentric numerical model, it is found that the gap between the jelly roll and steel case is the root of the different hoop strain on the steel case during the cycle. It is suggested that the gap (the diameter ratio of the jelly roll to steel case) need be focused in the engineering design for the cylindrical Li-ion battery cell with next-generation silicon composite electrode.

硅石墨复合电极是高能量和高功率密度18650锂离子电池的主要研究对象，而复合电极的大体积膨胀可能会导致电池的钢制外壳发生较大变形，甚至破裂。钢壳的机械可靠性对于电池的安全性和耐用性非常重要。在本文中，在18650锂离子电池工作期间对钢壳的环向应变进行了现场监测。在循环的早期阶段，钢壳的环向应变是由热膨胀引起的。经过长期循环（循环次数> 300次）后，在钢壳上发现了不均匀的应变分布，甚至是负应变。根据CT图像和非同心数值模型，结果发现，果冻卷和钢制外壳之间的间隙是循环过程中钢制外壳上不同的环向应变的根源。建议在具有下一代硅复合电极的圆柱形锂离子电池的工程设计中，应注意间隙（果冻卷与钢制外壳的直径比）。