Adaptive fast charging control using impedance-based detection of lithium deposition

Abstract

The recently introduced impedance-based detection method for the retrospective identification of lithium deposition is used in a long-term ageing study. Six lithium-ion cells are fast charged for 250 cycles with two different strategies, (i) constant-current constant-voltage and (ii) detection-based, adaptive charging control in which the current of the following step is controlled by the detection result of the previous step. The adaptive charging control leads intentionally to critical charging currents with minor lithium deposition effects for the majority of cases. Nevertheless, only marginal capacity fade can be observed after the whole long-term experiment, proving that the detection method reacts sensitively and reliably on minor lithium deposition. On the other hand, the adaptive charge control leads to significantly higher currents, thus reduced charging durations. Hence, the method qualifies for both adaptive fast charging control and for the identification of charging rate limits. A differential voltage analysis is performed before and after the long-term study, identifying the loss of lithium inventory, as well as the loss of anode active material as dominant degradation modes. Additionally, a sensitivity analysis with varying detection time and measurement accuracy is carried out to identify minimum measurement requirements and to increase the method’s time- and cost-efficiency.