Enhanced cycle life and capacity retention of dual electrolyte Li-ion capacitor through optimization of the solid electrolyte

Battery-supercapacitor hybrid devices bridge the gap between batteries and supercapacitors, offering high energy and power densities with excellent cycling stability. However, integrating their distinct energy storage mechanisms remains challenging. A strategy to address this challenge is advanced interphase engineering at the electrode|solid electrolyte junction. In this work, we present an optimized solid electrolyte (anolyte) for a layered graphite anode, designed to enhance lithium intercalation, mitigate lithium plating, and promote the formation of a stable Solid-Electrolyte Interphase (SEI) for a Lithium-Ion Capacitor (LiC). This approach significantly improves capacity retention and long-term stability, reaching 100 % over 3000 cycles and maintaining 96.6 % of the maximum capacity at 10,000 cycles, while also maintaining the anode potential below the operating voltage of lithiated graphite (<0.25 V vs Li|Li + ). These findings demonstrate a step toward high-performance hybrid capacitors with improved durability and energy storage capabilities. • Optimized alginate anolyte enables 100% capacity retention at 3,000 and 96.6% at 10,000 cycles. • Higher ionic liquid uptake (from 10% to 45%) in the ionogel increases LiFSI availability, promoting uniform SEI formation. • The hybrid capacitor maintains high energy density by keeping anode potential <0.25 V vs Li|Li⁺ throughout operation.