Lithium plating accurate detection of lithium-ion capacitors upon high-rate charging

Lithium-ion capacitors (LICs) offer higher power density and longer cycle life compared to lithium-ion batteries, and greater energy density than supercapacitors, making them ideal for applications requiring both high energy and power density. However, during high-rate charging, LIC anodes may suffer from lithium plating, a critical issue that remains unaddressed. To date, no direct analytical technique exists to study lithium plating behavior on LIC anodes. This study is the first to employ a 3-electrode pouch-type LICs, using differential analysis of the anode potential rather than the traditional terminal voltage approach, to accurately detect the charging rates at which lithium plating begins. We employed differential charging voltage (DCV), Coulombic efficiency (CE), and voltage relaxation profile (VRP) methods to comprehensively analyze lithium plating behavior. The feasibility of indirectly detecting lithium plating was validated by applying the CE and VRP methods to high-capacity 1,100 F LICs. The study found that lithium plating in LICs begins at a charging current of 20 C. The lithium deposited at currents below 50 C is reversible, while at currents above 50 C, irreversible dead lithium is formed. Furthermore, the study identified two reverse reactions following lithium deposition on the anode: lithium stripping and lithium intercalation. For soft carbon anodes, the potential difference between lithium stripping and intercalation was approximately 20 mV under relaxation conditions, and about 45 mV under constant voltage conditions. This research provides critical theoretical insights and practical guidance for optimizing LIC charging strategies.