Influence of the anode overhang on the open-circuit voltage and the ageing of lithium-ion batteries-A model based study

The anode overhang has been proven to be a non-negligible influencing factor in the ageing trajectory of lithium-ion batteries. It acts through the transfer of active lithium between the anode overhang and the active anode by changing reversibly the cell balancing. In this work, the anode overhang is proven to influence the open-circuit voltage. Through a high-precision measurement, a persistent rise of the open-circuit voltage was observed, which we have demonstrated to originate in the anode overhang effect. The dimensions and structure of the anode overhang were verified by a post-mortem analysis of the cell and matched with the voltage behaviour. Derived from this finding, an existing electrical-thermal ageing model was extended to allow the simulation of the interaction between the anode overhang and the capacity. With a Bayesian optimisation approach, the extended model allowed to drastically improve model parametrisation when ageing test data include an increase in capacity. The resulting model was verified with the simulation of two ageing profiles, each including varying ageing conditions and phases of capacity recovery. The model allows ageing predictions with a deviation below 4% of the remaining capacity after more than 750 days of ageing. The model is publicly available as part of an open-source project.

Automated summary

The anode overhang has a significant influence on the ageing trajectory of lithium-ion batteries. It affects the cell balancing by transferring active lithium between the anode overhang and the active anode. This study demonstrates that the anode overhang also influences the open-circuit voltage, leading to a persistent rise.