A Rapid Liquid Metal Battery Sorting Method Based on Ensemble Learning
Xia Junyi1, Shi Qionglin1, Jiang Kai2, He Yaling2, Wang Kangli1
1. State Key Laboratory of Advanced Electromagnetic Engineering and Technology School of Electrical and Electronic Engineering Huazhong University of Science and Technology Wuhan 430074 China; 2. Engineering Research Center of Power Safety and Efficiency Ministry of Education Wuhan 430074 China
Abstract Liquid metal battery (LMB) is a newly emerged battery technology for large scale energy storage, which requires massive batteries in group operation. Battery sorting, which could effectively reduce the inconsistency among batteries, is a useful method to significantly improve the performance of energy storage and reduce potential safety risks. However, because of the characteristics of LMB, including large capacity and small internal resistance, existing sorting methods, which mainly focus on lithium ion batteries, cannot meet the precision requirements of liquid metal battery sorting. In addition, these methods also require additional battery testing to obtain input features, thus there is room for further optimization of test time and cost. In order to address these issues, a rapid sorting method for liquid metal batteries based on ensemble learning is proposed. Combining the advantages of different models by adopting feature selection and ensemble learning methods, it precisely predicts the sorting index and conducts battery sorting with satisfactory accuracy. Firstly, a dataset is constructed based on LMB’s cycling data during activation, which comprises samples in 1D vector form. Secondly, features of the dataset are selected on the basis of a comprehensive method, which takes various aspects into consideration. Thirdly, three different base models are trained and optimized with the help of three-fold validation and grid search optimization, and then two ensemble model, which adopts voting and stacked ensemble method respectively, are trained based on these base models. Fourthly, all the models, including base models and ensemble ones, and a contrast model (neural network) are evaluated on the test set, which demonstrates the superiority of the stacked ensemble model. Finally, battery sorting is conducted on the basis of capacity predictions made by the stacked ensemble model. In this sorting method, the feature selection method reduces the dimension of data and selects the most effective features and ensemble methods integrate advantages of different base models, both of which contribute to the improvement of capacity predictions’ precision and reliability. Evaluation results on the test set show that the stacked ensemble model has the best performance, with a root mean square error (RMSE) of 0.227 8 A·h, a root mean square percentage error (RMSPE) of 0.455 6% and reliability of 97.42%. In contrast with the mainstream model neural network, its prediction error is reduced by 52.16% and the reliability is improved by 9.10%. Furthermore, compared with models without feature selection, all the models have better overall performance after feature selection, with better precision and higher reliability. Sorting results demonstrate that when the best model, the stacking ensemble model, is applied to LMB sorting, the proposed sorting method achieves both high accuracy and recall rate in battery sorting, which are 96.62% and 93.18% respectively. The following conclusions can be drawn from the evaluation and sorting results: (1) Compared with existing sorting methods, the proposed method not only saves a lot of time by utilizing data during the activation period instead of data from extra test but also achieves high accuracy and recall rate in battery sorting on the basis of a precise and reliable ensemble model. (2) The comprehensive feature selection method adopted by the proposed sorting method is effective. In a comparison of models without feature selection, models trained after feature selection, including base models and ensemble models, have achieved overall performance improvement with smaller errors and higher reliability. (3) The performance of the proposed ensemble model is not only better than the base model used for ensemble learning, but also superior to the mainstream neural network model on the basis of essential indicators such as model validation score, test set score, and reliability. Therefore, it is a promising model for sorting index prediction in LMB sorting applications.
Xia Junyi,Shi Qionglin,Jiang Kai等. A Rapid Liquid Metal Battery Sorting Method Based on Ensemble Learning[J]. Transactions of China Electrotechnical Society, 2023, 38(21): 5900-5912.
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2023, Vol. 38 
