Energy Storage Science and Technology ›› 2024, Vol. 13 ›› Issue (6): 2010-2021.doi: 10.19799/j.cnki.2095-4239.2023.0918

• Energy Storage Test: Methods and Evaluation • Previous Articles     Next Articles

Estimated state of health for retired lithium batteries using kernel function and hyperparameter optimization

Chen LI(), Huilin ZHANG(), Jianping ZHANG   

  1. School of Mechanical Engineering University of Shanghai for Science and Technology, Shanghai 200093, China
  • Received:2023-12-19 Revised:2023-12-31 Online:2024-06-28 Published:2024-06-26
  • Contact: Huilin ZHANG E-mail:lichen_2021720@163.com;zhanghuilin@usst.edu.cn

Abstract:

Given the uncertainty surrounding preretirement battery conditions, this study aims to advance the data-driven approach for accurately estimating retired lithium batteries' state of health (SOH). To achieve this, an enhanced SOH estimation method based on the Gaussian process regression (GPR) model is proposed. Initially, cyclic charge and discharge data from retired lithium batteries are gathered, and statistical health characteristics are derived to depict the aging properties. Methods such as capacity increment analysis (ICA) and electrochemical impedance spectroscopy (EIS) are employed to consider temperature effects. The Pearson correlation coefficient was used to assess the correlation between selected statistical features and health characteristics, identifying those highly correlated with SOH to eliminate the feature redundancy. Subsequently, acknowledging the limitations of individual kernel functions and conventional hyperparameter optimization techniques, a hybrid approach combining linear and diagonal square exponential kernel functions is introduced to better accommodate the diverse nature of battery SOH estimation tasks. The whale optimization algorithm (WOA) is then applied to optimize the hyperparameters of the estimation model, ensuring optimal fitting. This leads to the establishment of an improved GPR estimation model to enhance estimation accuracy. Finally, the effectiveness of the proposed method was validated using four different cells with varied initial health conditions from the NASA battery dataset. Results demonstrate the method's capability to provide accurate SOH estimation, with a mean absolute error below 1.75% and a root mean square error below 2.42%.

Key words: retired lithium-ion batteries, state of health, whale optimization algorithm, kernel functions, Gaussian process regression

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