Estimation of Cyclable Lithium for Li-ion Battery State-of-Health Monitoring

State of health (SOH) estimation for Li-ion batteries enables high-fidelity monitoring and high-performance in advanced battery management systems for applications such as mobile devices, electrified transportation, and energy storage. In order to achieve accurate SOH information, this paper improves the output voltage prediction by considering state-dependent parameters for a reduced-order electrochemical model. In addition, the SOH information is defined as the total moles of lithium in both solid-phase and electrolyte-phase, which directly affects the initial conditions of the electrochemical states in the model. We validate that the change of these parameters leads to capacity fade and power fade in terms of battery life cycling. The sensitivity equations are derived for these SOH parameters, and used to track the parameter changes via gradient-based parameter fitting algorithm. Simulation results demonstrate the proposed SOH estimation scheme using voltage and current measurements.