New Method for Characterization of the Open Circuit Potential Curve for Battery Cathode Materials

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Battery management system (BMS) is a key component of the battery for electric vehicles and portable electronics, as it guaranties reliable and safe operation of the battery, while ensuring its longevity and optimal performance. State-of-the-art BMS relies on an equivalent circuit model, while an important research topic is the development of BMS, which is based on an electrochemical model.[1] The main task of BMS is to accurately estimate the available energy and power of the battery by tracking its current state of charge (SOC). The open circuit voltage (OCV) of a cell is often used for estimation of the SOC of a battery. It depends on the open circuit potential (OCP) of the anode and the cathode materials, which give the potential associated with a certain amount of lithium stored in each structure. The accuracy of the OCP curves of each electrode material is critical for use with BMS based on electrochemical models, as in addition to tracking the bulk SOC of a battery, it also tracks the surface SOC.[1] As a result, BMS based on electrochemical models can offer improved prediction for both instantaneous and pulse power relative to systems based on an equivalent circuit model.In this contribution, we propose a novel method for characterization of the open circuit potential vs. state of lithiation (OCP) curves for active materials commonly used in lithium-ion batteries. Our method offers increased accuracy over existing electrochemical procedures [1-3]by providing a standardized mapping process from the measured gravimetric capacity to state of lithiation and improving characterization in the region of the curve that is close to the lithium content of 1. We demonstrate the strengths of the method on two different cathode materials: LiCoO2 and LiNi1/3Mn1/3Co1/3O2, which are widely used in commercial cells for portable electronics and electric vehicles. [2-3] 1. Chaturvedi, N. A., Klein, R., Christensen, J., Ahmed, J. & Kojic, A. Algorithms for Advanced battery-Management Systems. IEEE Control Syst. Mag. 49–68 (2010).2. Daniel, C., Mohanty, D., Li, J. & Wood, D. L. Cathode materials review. AIP Conf. Proc. 1597, 26–43 (2014).3. Cairns, E. J. & Albertus, P. Batteries for Electric and Hybrid-Electric Vehicles. Annu. Rev. Chem. Biomol. Eng. 1, 299–320 (2010).