Lithium-ion capacitor based on nanoarchitectured polydopamine/graphene composite anode and porous graphene cathode

Developing lithium ion capacitors (LICs) with high energy density is still challenging, due to the kinetic mismatch between the capacitor-type cathode and the battery-type anode. In addition, metal-free LICs are preferred over high-cost and unsustainable metal-containing electrode materials. Exploring appropriate metal-free cathode and anode materials with high capacity and excellent rate performance is one of the keys to attain such goal. Herein, nanoarchitectured graphene-based LICs are successfully constructed by using 2D polydopamine-graphene heterostructured anode and porous graphene cathode. The 2D nature of polydopamine-graphene facilitate the transport of electrolyte ions while graphene promotes electron transfer. The high specific surface area of the porous graphene endows ions with accessibility and fast transport. The metal-free LIC device achieves a high energy density (135.6 Wh kg⁻¹ at 210.4 W kg⁻¹), high power density (21.0 kW kg⁻¹ at 78.9 Wh kg⁻¹), high low-temperature performance (76.4 Wh kg⁻¹ at −20 °C), and reasonably long cycling life. This work provides an effective strategy to design metal-free LIC with high performance at wide temperature range.