A mathematical method for open-circuit potential curve acquisition for lithium-ion batteries

Abstract A half-cell test is often used to obtain electrode potentials for lithium-ion batteries when using an electrochemical model to simulate terminal voltage, which needs a series of time-consuming processes. However, this method generally requires expensive electrochemical measuring equipment, reference electrodes, and a vacuum glove box. This study develops a mathematical method for open-circuit potential curve acquisition. With a known open-circuit potential of the positive electrode and full-cell open-circuit voltage approximately measured at a low discharge rate of 0.02C, an open-circuit potential curve of the negative electrode can be calculated. A mathematical expression incorporating hyperbolic tangent functions and exponential functions with central coordinate positions against different lithiation states is then selected to describe the negative open-circuit potential. Finally, a least squares fitting method is adopted to identify the unknown coefficients in the expression. Five types of batteries are then tested to assess the accuracy and robustness of the method.