Domain knowledge-guided machine learning framework for state of health estimation in Lithium-ion batteries

Accurate estimation of battery state of health is crucial for effective electric vehicle battery management. Here, we propose five health indicators that can be extracted online from real-world electric vehicle operation and develop a machine learning-based method to estimate the battery state of health. The proposed indicators provide physical insights into the energy and power fade of the battery and enable accurate capacity estimation even with partially missing data. Moreover, they can be computed for portions of the charging profile and real-world driving discharging conditions, facilitating real-time battery degradation estimation. The indicators are computed using experimental data from five cells aged under electric vehicle conditions, and a linear regression model is used to estimate the state of health. The results show that models trained with power autocorrelation and energy-based features achieve capacity estimation with maximum absolute percentage error within 1.5% to 2.5% .

Taking Second-life Batteries from Exhausted to Empowered using Experiments, Data Analysis, and Health Estimation

The reuse of retired electric vehicle (EV) batteries in electric grid energy storage emerges as a promising strategy to address environmental concerns and boost economic value. This study concentrates on devising health monitoring algorithms for retired batteries (BMS$_2$) deployed in grid storage applications. Over 15 months of testing, we compile, analyze, and publicly share a dataset of second-life (SL) batteries, implementing a cycling protocol simulating grid energy storage load profiles within a 3 V-4 V voltage window. Four machine learning-based health estimation models, relying on BMS$_2$ features and initial capacity, are developed and compared, with the selected model achieving a Mean Absolute Percentage Error (MAPE) below 2.3% on test data. Additionally, an adaptive online health estimation algorithm is proposed by integrating a clustering-based method, limiting estimation errors during online deployment. These results constitute an initial proof of concept, showcasing the feasibility of repurposing retired batteries for second-life applications. Based on obtained data and representative power demand, these SL batteries exhibit the potential, under specific conditions, for over a decade of grid energy storage use.