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Emerging wearable electronics require stretchable energy storage devices to achieve energy autonomy for future commercialization. Stretchable microsupercapacitors (SMSCs) with neutral multivalent electrolytes are desired to increase the specific capacitance while addressing the safety concerns of using acidic/organic electrolytes near the human body. Ti3C2Tx MXene nanosheets exhibit attractive electrochemical properties for various energy storage applications, yet few MXene SMSCs with neutral electrolytes were reported. Herein, a two-step contraction process was developed for fabrication of MXene SMSCs with high specific capacitance. After thermal shrinkage and solvent-induced contraction, an elastomer-infiltrated MXene (e-MXene) device with miniaturized dimensions and interdigitated electrodes was obtained. Upon incorporating an acidic gel electrolyte, the e-MXene SMSC demonstrated high areal capacitance (CA, 127.9 mF cm−2), high rate performance (64.0% retention from 10 to 200 mV s−1), and high mechanical stability under 50% strain for 3000 cycles (91.6% preservation). Furthermore, the e-MXene SMSC with neutral multivalent electrolyte demonstrated high CA of 61.4 and 51.7 mF cm−2 under 0% and 50% strains, respectively. Compared with the literature, our e-MXene SMSC with acidic electrolyte showed superior energy density (5.4 μW h cm−2 at 0.15 mW cm−2), and the SMSC with neutral multivalent electrolyte demonstrated high electrochemical performance (3.1 μW h cm−2 at 0.03 mW cm−2) together with ensured user safety.

Excellent self-healability is considered as a critical element for next-generation flexible/wearable energy-storage devices. However, realizing superior electrochemical performances remains a big challenge for such devices because self-healability intrinsically offsets their basic energy-storage functions. Here we demonstrate that the conflict can be effectively addressed for a supercapacitor via rationally designing its device configuration at a molecular level. The capacitor is fabricated by in situ integrating polyaniline (PANI) and H2SO4 solution into a single network comprising the copolymer of vinylimidazole and hydroxypropyl acrylate (PVH). The all-in-one configuration combines fast charge-carrier transportation, good structural durability and excellent self-healability. Consequently, the resulting capacitor delivers a high specific areal capacitance and rate capability superior to its counterparts, but also maintains ultra-long cycling life even after breaking/healing 10 times. This example of configuration engineering offers a new and promising avenue to design self-healable energy-storage devices with outstanding performances.

Flexible, high-performance miniature supercapacitors that offer reliable energy storage and output are desirable for use in portable and wearable electronics. Herein, we developed micro-supercapacitors with three-dimensional electrodes by printing assembly of graphene. By controlling the microstructures and macroscopic architectures of the graphene electrodes, superior electrochemical performance was achieved; especially, we demonstrated an advancement to address the limitation of areal capacitance. The unique three-dimensional graphene structure also provides this new class of micro-supercapacitors with exceptional mechanical flexibility. With these remarkable features, facile integration of the micro-supercapacitor array into flexible printed circuits was demonstrated. This printing assembly approach will pave the way to explore energy storage systems with diverse structures and extended functionalities.

Herein, a facile and available electrochemical activation approach has been developed to markedly boost the capacitive performance of carbon fiber paper (CFP). The activated CFP could deliver a significant areal capacitance of 1.56 F cm−2 at a high current density of 5 mA cm−2 with excellent rate capability and cycling performance.

Porous single-crystalline nanosheet (NS) arrays of Co3S4 have been synthesized via a simple shape and phase transformation route, which exhibits high specific capacitance (1081 F g−1 at 1.61 A g−1) and areal capacitance (2.69 F cm−2 at 4 mA cm−2 and 2.33 F cm−2 at 12 mA cm−2) with good cycling performance (96.2% capacitance retention after 3000 cycles).

A symmetric micro-supercapacitor is constructed by electrochemically depositing manganese oxide onto micro-patterned current collectors. High surface-to-volume ratio of manganese oxide and short diffusion distance between electrodes give an ultra-high areal capacitance of 56.3 mF cm(-2) at a current density of 27.2 μA cm(-2).

Ni0.25Co0.75(OH)2 hierarchical nanowire@nanoplatelet arrays were prepared by an in situ conversion from Ni0.5Co1.5(OH)2CO3 nanowire arrays in a highly concentrated basic solution at room temperature. These unique hierarchical nanoarrays showed a 7 times larger areal capacitance and better rate capability than the precursive one-dimensional nanowire arrays.

We designed and fabricated supercapacitors by directly drawing graphite on cellulose paper. The supercapacitors show stable long cycling performance and a high areal capacitance of 2.3 mF cm−2, which is much higher than the literature reported values. This solvent-free deposition technique represents a low cost, highly scalable and versatile fabrication method for integrated paper-based energy devices.