Advances in micro-supercapacitors (MSCs) with high energy density and fast charge-discharge capabilities for flexible bioelectronic devices—A review

Supercapacitors are a new brand of high-performance nanoengineered devices that match the high capacity of batteries for electric energy storage with the ability of dry capacitors for ultra-fast charging or discharging rates. Thus, supercapacitors are capable of simultaneously providing the high energy-density and high power-density, demanded in a plethora of biosensors and portable electronic devices. In this review, a variety of nanomaterials investigated for possible applications in novel supercapacitors have been evaluated including different carbon nanoforms, metal oxides or hydroxides, chalcogenides, carbides and phosphates, as well as organic redox species, conductive polymers, metal-organic frameworks, MXenes and others. Different strategies for boosting volumetric capacitance, power density and charge or discharge cycling stability of micro-supercapacitors (MSCs) designed from these materials have been reviewed and their application potential assessed. Special attention has been given to micro-supercapacitor's designs that are suitable for miniaturization and integration with flexible microcircuits for wearable and implantable biomedical devices, remotely rechargeable sensors, microprocessor-controlled data processing chips, biomorphic computing, smart phone communication, military, automotive applications and emerging technologies. The different strategies applied for MSCs design and fabrication, including femto-laser writing, photolithography, screen printing, stamping, inkjet printing, mask patterning and others, have been assessed. The exciting future perspectives of MSCs have been discussed.