Lithium-ion cell equivalent circuit model identification by galvanostatic intermittent titration technique

When modelling lithium-ion batteries thorough identification of parameters across the entire operation domain is necessary to capture non-linear variations of properties caused by temperature or state of charge. This work presents a parameter identification method using galvanostatic intermittent titration technique (GITT) to create high resolution look-up tables and response surfaces for equivalent circuit models (ECM). Significant improvements are proposed over other parameter estimation method, such as HPPC. These improvements are open-circuit voltage change compensation, and ohmic resistance correction, which yield to better overall accuracy of the model. An iterative parameter identification algorithm (IPIA) is introduced to increase the robustness of the non-linear least square curve fitting for higher orders ECM. The method is applied to identify the parameters of 1RC and a 2RC ECM. The use of GITT in conjunction with IPIA has allowed greater fidelity of model response surfaces than previously published pulse identification methods. Experiments were conducted on Nickel-Manganese-Cobalt cathode lithium-ion cells. The methodology presented in this paper is intended to be applicable to any lithium-ion battery format or chemistry with minor adjustments.