Off-line method to determine the electrode balancing of Li-ion batteries

In this paper, we propose a non-invasive method to determine the electrode balancing of the lithium-ion batteries, which is the determination of (i) individual electrodes capacities and (ii) individual curves of equilibrium potentials of the electrodes as functions of the battery state of charge. The proposed method requires the average measurements of the battery voltage between discharge and charge for a low current. This averaged voltage is then associated with the reference average curves of the electrode equilibrium potentials issued from literature. To determine the electrode balancing, the method was first used on a pristine LiFePO4/graphite cell. The results are consistent with this cell data and the proposed method accuracy is compared to a reference method of the literature. We then used the proposed method on an aged cell of the same type to evaluate the method robustness with respect to the change in the cell state of health. The tracking of each electrode capacity during the battery lifespan can be used as a non-invasive diagnosis tool to monitor the state of health evolution to each electrode. Furthermore, the access to the individual curves of electrodes equilibrium potentials as functions of the battery state of charge is the first step towards the implementation of a non-invasive tool for an optimal prediction of the battery operating limits during fast recharging.