Battery Internal Short Detection Methodology Using Cell Swelling Measurements

Li-ion battery internal short circuits are a major safety issue for electric vehicles, and can lead to serious consequences such as battery thermal runaway. An internal short can be caused by mechanical abuse, high temperature, overcharging, and lithium plating. The low impedance or hard internal short circuit is the most dangerous kind. The high internal current flow can lead to battery temperature increase, thermal runaway, and even explosion in a few seconds. Algorithms that can quickly detect such serious events with a high confidence level and which are robust to sensor noise are needed to ensure passenger safety. False positives are also undesirable as many thermal runaway mitigation techniques, such as activating pyrotechnic safety switches, would disable the vehicle. Conventional methods of battery internal short detection, including voltage and surface temperature based algorithms, work well for a single cell. However, these methods are difficult to apply in large scale battery packs with many parallel cells. In this study, we propose a new internal short detection method by using cell swelling information during the early stages of a battery heating caused by an internal short circuit. By measuring cell expansion force, higher confidence level detection can be achieved for an internal short circuit in an electric vehicle scale battery pack.

锂离子电池内部短路是电动汽车的一个主要安全问题，可能导致电池热失控等严重后果。内部短路可能由机械滥用、高温、过充和锂枝晶生长引起。低阻抗或硬性内部短路是最危险的类型。内部的高电流会导致电池温度升高、热失控，甚至在几秒钟内爆炸。为确保乘客安全，需要能够以高置信度快速检测此类严重事件且对传感器噪声具有鲁棒性的算法。误报也是不可取的，因为许多热失控缓解技术，如激活烟火式安全开关，会使车辆无法使用。传统的电池内部短路检测方法，包括基于电压和表面温度的算法，对单个电池单元效果良好。然而，这些方法很难应用于具有许多并联电池单元的大规模电池组。在这项研究中，我们提出了一种新的内部短路检测方法，该方法利用内部短路引起的电池发热早期阶段的电池膨胀信息。通过测量电池膨胀力，可以在电动汽车规模的电池组中对内部短路实现更高置信度的检测。