Model-based lithium deposition detection method using differential voltage analysis

During fast charging of lithium-ion batteries with graphite electrodes, kinetic limitations of the desired intercalation process force the Li ions to deposit metallically on the electrode's surface. The degradation process of lithium deposition (LD) leads to rapid capacity fade and may lead to safety-critical conditions. Hence, a reliable and sensitive method for the operando detection of LD is needed that allows to adjust the charging current and to preserve the lifetime of the battery. Differential voltage analysis is a state-of-the-art electrochemical characterisation technique that enables the retrospective detection of LD during relaxation and discharge. However, in its current use it reveals weaknesses in terms of reliability and sensitivity. Our novel, model-based approach distinguishes normal, i.e., after intercalation only, and LD-affected relaxation. Hence, the charging process can be classified as critical or non-critical in terms of accelerated ageing. To test the method on real fast charging cycles, a measurement series with six commercial cells and different applied charging currents is performed, and the subsequent voltage behaviour during relaxation and discharge is investigated. As reference, the irreversible charge loss is measured for each cycle using coulomb counting. A detection algorithm is developed, which shows a remarkable sensitivity and furthermore enables an automated detection of LD.