Analysis and detection of lithium deposition after fast charging of lithium-ion batteries by investigating the impedance relaxation

Lithium deposition (LD) is a harmful degradation mechanism of lithium-ion batteries with intercalation electrodes induced by fast charging, especially at low temperatures. For the prevention of an accelerate ageing under fast charging conditions it is crucial, first, to analyse the cell behaviour, to identify critical charging events and to detect LD. Second, to reduce irreversible effects of LD the charging rate needs to be adjusted depending on the detection result. A sensitive, reliable, and automated operando detection method based on the impedance relaxation behaviour is developed. Results are shown for both a high-power and a high-energy cell type at a minimum of four different, critical and uncritical C-rates. Two complementary methods are used to detect irreversible LD, the coulombic efficiency and the dilation method. For the detection of reversible LD the differential voltage analysis and the newly developed impedance relaxation method are applied. Characteristic frequencies of anodic processes are identified using impedance spectroscopy to enable a mechanistic interpretation of the occurring phenomena. The impedance behaviour during relaxation reveals a reproducible anomaly that detects LD with a high sensitivity and reliability. A detection algorithm is introduced, which indicates the likelihood that metallic lithium was deposited during charging within short relaxation times.