Experimental Investigation of Fast Charging Protocols Over Aging Using Multilayer Pouch Cells with Silicon-Dominant Anodes

Fast charging (FC) capability is a frequently mentioned advantage of silicon as an anode active material for lithium-ion cells. In this work, the FC capability of multilayer pouch-cells containing 70 wt% silicon anodes and NCA cathodes is investigated over aging. Based on a physicochemical-thermal model, voltage trajectories are derived based on the constant anode potential (CAP). Different safety margins are used to derive different aggressive FC protocols. These voltage trajectories are experimentally applied to the cells, which are aged until 70% state-of-health (SoH) using the different FC protocols in different state-of-charge (SoC) windows. The resulting capacity retention was improved to almost 850 cycles at 70% SoH using the 50% ΔSoC window. FC times of ≈10 min for 50% ΔSoC and ≈19 min for 70% ΔSoC were achieved. The subsequent degradation mode analysis indicated the loss of lithium inventory (LLI) as the main aging mechanism, independent of the FC protocols. The LLI changed the cell balancing, causing the FC time to increase by a factor of up to 3, depending on the safety margins and ΔSoC. Finally, the post-mortem analysis confirmed the LLI as the main and the loss of active material of the anode and cathode only as minor degradation modes.