The rapid development of printable electronic devices with flexible and wearable characteristics requires supercapacitor devices to be printable, light, thin, integrated macro- and micro-devices with flexibility. Herein, we developed a consecutive spray printing strategy to controllably construct and integrate diverse supercapacitors on various substrates. In such a strategy, all supercapacitor components are fully printable, and their thicknesses and shapes are well controlled. As a result, supercapacitors obtained by this strategy achieve diverse structures and shapes. In addition, different nanocarbon and pseudocapacitive materials are applicable for the fabrication of these diverse supercapacitors. Furthermore, the diverse supercapacitors can be readily constructed on various objects with planar, curved, or even rough surfaces (e.g., plastic film, glass, cloth, and paper). More importantly, the consecutive spray printing process can integrate several supercapacitors together in the perpendicular and parallel directions of one substrate by designing the structure of electrodes and separators. This enlightens the construction and integration of fully printable supercapacitors with diverse configurations to be compatible with fully printable electronics on various substrates.Keywords: carbon nanotube; diverse structures; printable; spray printing; supercapacitor;

Freestanding reduced graphene oxide–sulfur (rGO–S) composite films were fabricated by combining solution infiltration of sulfur into solvated rGO films with freeze-drying. Such rGO–S composite films can directly serve as the cathodes of lithium–sulfur (Li–S) batteries. The nanostructured architecture of rGO–S composite films considerably improved the cycling stability of Li–S batteries.

Carbon fiber cloth/sulfur (CFC/S) composites were prepared by loading sulfur in the carbon fiber cloth (CFC) that was obtained by carbonizing the renewable cotton cloth. The CFC/S composites are the excellent cathodes of room-temperature sodium-sulfur (RT Na-S) batteries due to their three-dimensional (3D) interconnected network and high electrolyte uptake of 1156%. The CFC/S composite with area sulfur loading of 2 mg cm−2 displays an initial discharge capacity of 390 mA h g−1 at 0.1 C (1 C=1675 mA g−1) and a capacity of 120 mA h g−1 after 300 cycles with tetra ethylene glycol dimethyl ether liquid electrolyte. Furthermore, since the freestanding CFC/S composites exhibit good flexibility and conductivity, they can serve as the cathodes of flexible RT Na-S batteries. As a proof of concept, the soft-packaged RT Na-S batteries were fabricated. The capacity of soft-packaged RT Na-S batteries can remain stable when the batteries are bent.Carbon fiber cloth/sulfur (CFC/S) composites were prepared by loading sulfur in the carbon fiber cloth (CFC) that was obtained by carbonizing the renewable cotton cloth. The CFC/S composites are the excellent cathodes of room-temperature sodium-sulfur (RT Na-S) batteries due to their interconnected network and high electrolyte uptake. Soft-packaged RT Na-S batteries based on CFC/S composites can remain stable electrochemical properties at bending state.Download high-res image (264KB)Download full-size image

•Highly stretchable integrated system for micro-supercapacitors with AC line filtering and UV detector were fabricated.•The integrated system can be readily designed into diverse structures and shapes.•The integrated device can still show stable photocurrent response and AC line filtering even stretched up to 200%.In-plane micro-supercapacitors (MSCs) possess higher volumetric energy density and are thus more compact compared with traditional aluminum electrolytic capacitors (AECs). As a result, developing in-plane MSCs with AC line filtering function is desired to replace the AECs and integrate with other electronic devices. Here, highly stretchable integrated system for in-plane MSCs with AC line filtering and UV detector were fabricated by designing buckled micro-electrodes based on SWCNT film and TiO2 NPs. Although gel electrolyte was used in these MSCs, they still show an ultrafast frequency response with a phase angle of -75.2° because of their unique structure. Such MSCs thus can function as the AC line filtering devices. Furthermore, their AC line filtering behavior remains almost unchanged even stretched up to 200%. Further coating TiO2 NPs on the buckled SWCNT micro-electrodes is able to endow the MSCs with another ability of UV photodetection with the sensitivity of 6.2. Importantly, such integrated device can still show stable photocurrent response and capacitance behaviors at different stretching times and even repeated stretching 100 times. The rational design of such stretchable integrated system for MSCs with AC line filtering and UV photodetector will pave the way for the applications in assembling supercapacitors and other electronics into highly stretchable integrated devices.Highly stretchable integrated system with micro-supercapacitor and UV photodetector were fabricated by designing buckled micro-electrodes based on SWCNT film and TiO2 NPs. Such integrated device can still show stable photocurrent response and capacitance behaviors at 200% stretching strain.Download high-res image (204KB)Download full-size image

A critical challenge in fabricating the electrodes of flexible supercapacitors is to optimize their electrochemical performance without deteriorating their mechanical properties. We report here a strategy to prepare freestanding reduced graphene oxide@polyvinyl alcohol (rGO@PVA) composite films by synchronously reducing and assembling GO sheets with PVA molecules on a metal surface. Such rGO@PVA composite films realize the controllable assembly of rGO sheets and PVA in an ordered layered structure as well as the molecular level couplings between rGO sheets and PVA molecules. As a result, the rGO@PVA composite films display extremely high strength and Young's modulus. After introducing H2SO4, the PVA/H2SO4 electrolyte layer between rGO sheets can form fast ion transport channel at the molecular level in the composite films. Therefore, the composite films deliver high volumetric capacity (206.8 F cm−3), excellent energy density (7.18 mW h cm−3) and power density (2.92 W cm−3). More importantly, the supercapacitors based on the composite films show stable electrochemical performance under different stresses and bending states, even when the supercapacitors were bent to 180°. The high flexibility and electrochemical performance of such supercapacitors will enable a broad field of energy-storage devices to be compatible with flexible and wearable electronics.

As energy storage devices, supercapacitors that are also called electrochemical capacitors possess high power density, excellent reversibility and long cycle life. The recent boom in electronic devices with different functions in transparent LED displays, stretchable electronic systems and artificial skin has increased the demand for supercapacitors to move towards light, thin, integrated macro- and micro-devices with transparent, flexible, stretchable, compressible and/or wearable abilities. The successful fabrication of such supercapacitors depends mainly on the preparation of innovative electrode materials and the design of unconventional supercapacitor configurations. Tremendous research efforts have been recently made to design and construct innovative nanocarbon-based electrode materials and supercapacitors with unconventional configurations. We review here recent developments in supercapacitors from nanocarbon-based electrode materials to device configurations. The advances in nanocarbon-based electrode materials mainly include the assembly technologies of macroscopic nanostructured electrodes with different dimensions of carbon nanotubes/nanofibers, graphene, mesoporous carbon, activated carbon, and their composites. The electrodes with macroscopic nanostructured carbon-based materials overcome the issues of low conductivity, poor mechanical properties, and limited dimensions that are faced by conventional methods. The configurational design of advanced supercapacitor devices is presented with six types of unconventional supercapacitor devices: flexible, micro-, stretchable, compressible, transparent and fiber supercapacitors. Such supercapacitors display unique configurations and excellent electrochemical performance at different states such as bending, stretching, compressing and/or folding. For example, all-solid-state simplified supercapacitors that are based on nanostructured graphene composite paper are able to maintain 95% of the original capacity at a 180° folding state. The progress made so far will guide further developments in the structural design of nanocarbon-based electrode materials and the configurational diversity of supercapacitor devices. Future developments and prospects in the controllable assembly of macroscopic nanostructured electrodes and the innovation of unconventional supercapacitor configurations are also discussed. This should shed light on the R&D of supercapacitors.

A critical challenge in fabricating the electrodes of flexible supercapacitors is to optimize their electrochemical performance without deteriorating their mechanical properties. We report here a strategy to prepare freestanding reduced graphene oxide@polyvinyl alcohol (rGO@PVA) composite films by synchronously reducing and assembling GO sheets with PVA molecules on a metal surface. Such rGO@PVA composite films realize the controllable assembly of rGO sheets and PVA in an ordered layered structure as well as the molecular level couplings between rGO sheets and PVA molecules. As a result, the rGO@PVA composite films display extremely high strength and Young's modulus. After introducing H2SO4, the PVA/H2SO4 electrolyte layer between rGO sheets can form fast ion transport channel at the molecular level in the composite films. Therefore, the composite films deliver high volumetric capacity (206.8 F cm−3), excellent energy density (7.18 mW h cm−3) and power density (2.92 W cm−3). More importantly, the supercapacitors based on the composite films show stable electrochemical performance under different stresses and bending states, even when the supercapacitors were bent to 180°. The high flexibility and electrochemical performance of such supercapacitors will enable a broad field of energy-storage devices to be compatible with flexible and wearable electronics.

As energy storage devices, supercapacitors that are also called electrochemical capacitors possess high power density, excellent reversibility and long cycle life. The recent boom in electronic devices with different functions in transparent LED displays, stretchable electronic systems and artificial skin has increased the demand for supercapacitors to move towards light, thin, integrated macro- and micro-devices with transparent, flexible, stretchable, compressible and/or wearable abilities. The successful fabrication of such supercapacitors depends mainly on the preparation of innovative electrode materials and the design of unconventional supercapacitor configurations. Tremendous research efforts have been recently made to design and construct innovative nanocarbon-based electrode materials and supercapacitors with unconventional configurations. We review here recent developments in supercapacitors from nanocarbon-based electrode materials to device configurations. The advances in nanocarbon-based electrode materials mainly include the assembly technologies of macroscopic nanostructured electrodes with different dimensions of carbon nanotubes/nanofibers, graphene, mesoporous carbon, activated carbon, and their composites. The electrodes with macroscopic nanostructured carbon-based materials overcome the issues of low conductivity, poor mechanical properties, and limited dimensions that are faced by conventional methods. The configurational design of advanced supercapacitor devices is presented with six types of unconventional supercapacitor devices: flexible, micro-, stretchable, compressible, transparent and fiber supercapacitors. Such supercapacitors display unique configurations and excellent electrochemical performance at different states such as bending, stretching, compressing and/or folding. For example, all-solid-state simplified supercapacitors that are based on nanostructured graphene composite paper are able to maintain 95% of the original capacity at a 180° folding state. The progress made so far will guide further developments in the structural design of nanocarbon-based electrode materials and the configurational diversity of supercapacitor devices. Future developments and prospects in the controllable assembly of macroscopic nanostructured electrodes and the innovation of unconventional supercapacitor configurations are also discussed. This should shed light on the R&D of supercapacitors.