Estimating Lithium-Ion Battery Electrode OCP without Cell Teardown*

Electrode open-circuit potential (OCP) is an intrinsic electrochemical property unique to the electrode material within a lithium-ion battery. It is critical to develop models of electrode OCP for accurate physics-based cell models used in modeling, estimation, and control applications. Measuring this relationship directly requires cell teardown, a costly procedure that destroys the cell. It is beneficial to develop alternative methods to estimate OCP avoiding teardown. This paper develops a series of methods to estimate electrode OCP using only cell open-circuit voltage (OCV) tests and a literature estimate of a known electrode OCP. We develop two main methods which were implemented in MATLAB. The first estimates the positive-electrode OCP using a given multi-species multi-reaction (MSMR) model of the negative electrode’s OCP. The second estimates the negative-electrode OCP assuming an MSMR model of the positive-electrode’s OCP with a separate procedure developed for LFP//graphite cells. Results were compared to measured cell OCV and electrode OCP. While these methods are heuristic, attempts to development mathematical algorithms to solve this problem have fallen short due to fundamental unobservability. We conclude that these methods might suit an AI application. These methods demonstrate that it is possible to find an estimate of electrode OCP without cell teardown as long as at least one of the electrode materials is known.