Entire ultrathin two-dimensional pseudocapacitive nanosheets with high active covalent groups for flexible asymmetric all-solid-state micro-pseudocapacitors with high energy density and long cycle life

Micro-supercapacitors (MSCs) are gradually emerging as a strong contender for the next wearable and portable micro-energy storage devices. Low energy density and poor stability are significant challenges to their widespread application. Based on this, a novel asymmetric all-solid-state Micro-pseudocapacitors (AMPCs) is designed elaborately, in which all the active materials are based on conducting two-dimensional (2D) materials with thin lamellar thickness and active covalent groups on the surface. The positive electrode was made of covalently graft-modified GO with p-phenylenediamine (PrGO), while the negative electrode was made of MXene material. Besides, electrochemically exfoliated graphene (EG) was incorporated into the positive electrode to further improve the electrochemical performance of the PrGO@EG hybrid film electrode due to its excellent conductivity and favorable π-π stacking effects. As a result, the PrGO@EG-30 % electrode demonstrates a high specific capacity of 571 F cm −3 (411 F/g) and maintains excellent stability, retaining 100 % of its capacity even after 10,000 cycles. Surprisingly, the assembled-designed PrGO@EG//MXene AMPCs achieved remarkable electrochemical performance in solid-state electrolytes with a notable capacity of 185.4 F cm −3 (84.6 F/g), impressive stability with 100 % retention after 10,000 cycles, and outstanding volumetric energy density up to 50.5 μWh cm −3 , exceeding the majorities of other state-of-the-art MSCs. Moreover, the microdevices can be easily integrated and electrochemically stable under various bending conditions, demonstrating their significant potential as flexible micro-energy storage devices.