Li-ion battery electrode state of charge and degradation monitoring using battery casing as the reference electrode

Abstract

Lithium-ion battery (LIB) internal state such as state of charge (SOC), electrode capacity, and available lithium-ion monitoring is helpful for effective battery degradation monitoring. Monitoring these internal parameters is challenging due to the weak observability of the electrode parameters and lack of information about available lithium-ion contents in the cell. A reference electrode can be useful to measure the electrode potentials, which can provide information about the internal states, SOC, electrode capacity, and the available lithium-ions in the cell. In this thesis, we proposed a novel three-electrode battery setup approach using battery casing for electrode parameter estimation and degradation monitoring. The presented work introduces a curve matching algorithm to estimate electrode capacity, SOC, and available lithium-ion in the cell and an unknown input observer to estimate anode SOC and capacity. Further, electrode and cell degradation are analyzed by comparing the capacity. The proposed reference electrode setup has less impact on cell degradation compared to the existing reference electrode setup methods. In contrast, the proposed method is practically feasible regarding the practical application of three-electrode batteries for electrode level parameter estimation and available lithium-ion monitoring in the cell.