The estimation of State of Health (SOH) constitutes the fundamental basis for performance optimization and fault diagnosis of battery management systems under realistic operating conditions. This study aims to investigate the intrinsic correlations among battery capacity degradation, permanent expansion rate, and Electrochemical Impedance Spectroscopy (EIS) through detailed measurement and analysis of prismatic electric bicycle batteries before and after service. Firstly, by analyzing the internal inconsistencies within the module, it is identified that there is a close relationship between SOH and permanent thickness expansion rate. Secondly, Equivalent Circuit Models (ECMs) are fitted and Distribution of Relaxation Times (DRT) analysis is conducted with varying regularization parameters to examine the variations in EIS in relation to SOH and expansion rate. Subsequently, a novel empirical model is proposed for SOH estimation by introducing the permanent thickness expansion rate as new dimension, departing from the traditional models that utilize aging cycle counts. To extend the model's applicability, data from both pouch and prismatic batteries are evaluated, resulting in high values of 0.994 and 0.945, respectively. This research is helpful in comprehending battery aging mechanisms and forecasting battery lifetime, offering valuable theoretical and practical insights for the advancement of battery state estimation.

中文翻译：

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基于方形电池永久膨胀的电化学阻抗和健康状态分析

健康状态（SOH）的估计是电池管理系统在实际运行条件下性能优化和故障诊断的基本依据。本研究旨在通过对方形电动自行车电池使用前后的详细测量和分析，探讨电池容量退化、永久膨胀率和电化学阻抗谱（EIS）之间的内在相关性。首先，通过分析模块内部的不一致性，发现SOH与永久厚度膨胀率之间存在密切关系。其次，拟合等效电路模型 (ECM)，并使用不同的正则化参数进行弛豫时间分布 (DRT) 分析，以检查 EIS 相对于 SOH 和膨胀率的变化。随后，通过引入永久厚度膨胀率作为新维度，提出了一种新颖的 SOH 估计经验模型，与利用老化循环计数的传统模型不同。为了扩展模型的适用性，对软包电池和方形电池的数据进行了评估，分别得出 0.994 和 0.945 的高值。这项研究有助于理解电池老化机制和预测电池寿命，为电池状态估计的进步提供有价值的理论和实践见解。