Real-time estimation of negative electrode potential and state of charge of lithium-ion battery based on a half-cell-level equivalent circuit model

Equivalent circuit models (ECMs) have been widely used for capturing the electrical behaviour of lithium-ion batteries (LIBs). However, one limitation of the conventional full-cell level ECM is that it cannot capture the battery's internal states at half-cell level, e.g., the negative electrode (NE) potential. Real-time monitoring of NE potential is highly desirable for improving battery performance and safety, as it can prevent lithium plating which occurs when the NE potential drops below a threshold value. This paper proposes an easy-to-implement framework for real-time estimation of the NE potential of LIBs. An ECM at half-cell level is developed and parametrised by a bespoke experimental method, exemplified on a commercial 21700 LIB cell. The cell is instrumented with a lithium reference electrode that enables direct measurement of the per-electrode potential. Based on the developed model, an extended Kalman filter is implemented to estimate the battery's NE potential and SoC in real-time using only onboard available signals including the terminal current and voltage. Experimental results show that the proposed method achieves high modelling and estimation accuracy. The root mean square error of the real-time NE potential estimation is below 8 mV. The low computational complexity of the developed algorithm can facilitate practical implementation in commercial BMS.