David Pech

Ultrahigh-power micrometre-sized supercapacitors based on onion-like carbon

Electrochemical capacitors, also called supercapacitors, store energy in two closely spaced layers with opposing charges, and are used to power hybrid electric vehicles, portable electronic equipment and other devices. By offering fast charging and discharging rates, and the ability to sustain millions of cycles, electrochemical capacitors bridge the gap between batteries, which offer high energy densities but are slow, and conventional electrolytic capacitors, which are fast but have low energy densities. Here, we demonstrate microsupercapacitors with powers per volume that are comparable to electrolytic capacitors, capacitances that are four orders of magnitude higher, and energies per volume that are an order of magnitude higher. We also measured discharge rates of up to 200 V s(-1), which is three orders of magnitude higher than conventional supercapacitors. The microsupercapacitors are produced by the electrophoretic deposition of a several-micrometre-thick layer of nanostructured carbon onions with diameters of 6-7 nm. Integration of these nanoparticles in a microdevice with a high surface-to-volume ratio, without the use of organic binders and polymer separators, improves performance because of the ease with which ions can access the active material. Increasing the energy density and discharge rates of supercapacitors will enable them to compete with batteries and conventional electrolytic capacitors in a number of applications.

Microsupercapacitors as miniaturized energy-storage components for on-chip electronics

The push towards miniaturized electronics calls for the development of miniaturized energy-storage components that can enable sustained, autonomous operation of electronic devices for applications such as wearable gadgets and wireless sensor networks. Microsupercapacitors have been targeted as a viable route for this purpose, because, though storing less energy than microbatteries, they can be charged and discharged much more rapidly and have an almost unlimited lifetime. In this Review, we discuss the progress and the prospects of integrated miniaturized supercapacitors. In particular, we discuss their power performances and emphasize the need of a three-dimensional design to boost their energy-storage capacity. This is obtainable, for example, through self-supported nanostructured electrodes. We also critically evaluate the performance metrics currently used in the literature to characterize microsupercapacitors and offer general guidelines to benchmark performances towards prospective applications.

3D RuO₂ Microsupercapacitors with Remarkable Areal Energy.

Large areal capacitance electrodes made of ruthenium oxide on highly porous gold current collectors are realized by an attractive approach. The hybrid structure exhibits a capacitance in excess of 3 F cm(-2) and an areal energy density for all-solid-state microsupercapacitors that is comparable to those of microbatteries.

High-resolution on-chip supercapacitors with ultra-high scan rate ability

A simple approach for the fabrication of high-resolution on-chip supercapacitors with increased performances is demonstrated. The resulting micro-devices display high specific cell capacitance (3 mF cm−2 using a hydrous ruthenium oxide electrode) and impressive scan rate abilities, up to 10000 V s−1 for multi-walled carbon nanotube based micro-supercapacitors, which is five orders of magnitude higher than those of conventional supercapacitors.

High resolution electrochemical micro-capacitors based on oxidized multi-walled carbon nanotubes

This study reports the preparation of all-solid-state micro-supercapacitors in planar interdigitated configuration based on MWCNTs via the electrophoretic deposition technique. The carbon nanotubes were functionalized with carboxylic groups via a HNO3 concentric solution in order to prevent their agglomeration and obtain a stable aqueous suspension, and to add a pseudo-capacitance contribution to the predominant double-layer capacitance. The electrode materials were characterized in a 3 electrode configuration, and the micro-devices in a two-electrode configuration using electrochemical impedance spectroscopy and cyclic voltammetry in 0.5 M sulfuric acid and a gel of PVA-H3PO4-H2O doped by SiWA electrolyte. Spatial resolution down to 10 μm was obtained for the device with specific capacitance up to 1.8 mF.cm−2 in electrolyte based PVA and a high power density of 1.28 W.cm−2 in 0.5 M H2SO4 electrolyte.

Potentialities of micro-supercapacitors as energy storage buffers in embedded micro-systems

Thanks to their unique properties and potential applications in various smart electronic devices, micro-supercapacitors have been increasingly investigated for on-chip energy storage. In this presentation, we describe our most recent attempts to increase the areal capacitance and energy of micro-supercapacitors. We deposited hydrated ruthenium oxide onto a highly porous gold current collector to realize a 3D electrode with unprecedented performances, fully compatible with current micro-fabrication and silicon-based device technology. The resulting electrode exhibits a capacitance per surface area in excess of 3 F.cm-2, and - for the first time - an all-solid-state micro-supercapacitor with a specific energy per surface area comparable to that of lithium-ion micro-batteries has been achieved, but with superior power and cycling stability.

Electrophoretic deposition of Li4Ti5O12 nanoparticles with a novel additive for Li-ion microbatteries

Electrophoretic deposition is presented as a handy and cost-effective technique to transfer nano-sized (powdered) electrode materials into thin- or thick-films for electrochemical energy storage applications. Electrophoretic deposition of Li4Ti5O12 nanoparticles is studied to prepare thick films as anodes for Li-ion microbatteries with MgCl2 additives – for the first time – as an efficient charging agent and a source of binder simultaneously. Electrochemical measurements in lithium test cells confirmed that the prepared thick-film Li4Ti5O12 electrode has good discharge (lithiation) capacities and cyclability, as well as good electronic and Li+ transport properties. Indeed, electrophoretic deposition is demonstrated to be a suitable alternative to prepare self-supported micro- or nano-structured Li4Ti5O12 for Li-ion microbatteries.