3D microbatteries are proposed as a step change in the energy and power per footprint of surface mountable rechargeable batteries for microelectromechanical systems (MEMS) and other small electronic devices. Within a battery electrode, a 3D nanoarchitecture gives mesoporosity, increasing power by reducing the length of the diffusion path; in the separator region it can form the basis of a robust but porous solid, isolating the electrodes and immobilising an otherwise fluid electrolyte. 3D microarchitecture of the whole cell allows fabrication of interdigitated or interpenetrating networks that minimise the ionic path length between the electrodes in a thick cell. This article outlines the design principles for 3D microbatteries and estimates the geometrical and physical requirements of the materials. It then gives selected examples of recent progress in the techniques available for fabrication of 3D battery structures by successive deposition of electrodes, electrolytes and current collectors onto microstructured substrates by self-assembly methods.

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High surface area mesoporous polyaniline (M-PANI) films can be produced on the surface of glassy carbon electrodes by the electrochemical polymerization from a composite made by mixing a Brij 98 surfactant with a water solution of aniline and sulfuric acid. The surfactant serves as a structure directing agent. When the quantity of Brij 98 in the composite was 45% by weight, it formed a hexagonal phase that comprises a template of cylinders arranged on a hexagonal lattice with a hydrophilic core. The aniline monomer infiltrated the core of the templates. When the potential of the glassy carbon electrode was cycled, the polymerization occurred inside the hollow core and cast it with the PANI film. Subsequently, the Brij 98 template was removed by a thorough washing with water to produce a well-ordered M-PANI film. The structure and the surface morphology of the M-PANI films were fully characterized by a scanning electron microscope and a transmission electron microscope. The electrochemical capacitance properties were investigated using electrochemical techniques, e.g., cyclic voltammetry, galvanostatic cycling and electrochemical impedance. The data showed a significant increase in the specific capacitance (as high as 532 F g −1 ) of the M-PANI films when compared with a non M-PANI electrode, which delivered a specific capacitance of 228 F g Supercapacitors, also known as electrochemical capacitors, have attracted immense attention as one type of efficient energy storage device because of their unique capability to store and release the charge at a very high rate.1,2 Supercapacitors store electrical charges at the interface between high surface area electrodes and liquid electrolytes. The energy stored in supercapacitors comes from the non-faradaic current due to charging of the electrical double layer as well as the pseudocapacitance produced by the faradaic current, which is caused by oxidation-reduction processes that take place at the surface of the electroactive materials.3-5 Therefore, supercapacitors could store capacitances several orders of magnitude higher than conventional capacitors while still maintaining the unique advantage of a high power density and exhibiting excellent reversibility with a long life cycle. 6,7 Many materials have been used to fabricate supercapacitor electrodes, such as carbon 8 and metal oxides, e.g., RuO 2 and NiO x . 9,10Also, conducting polymers of polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), and polythiophene are widely employed as electrode materials in supercapacitor applications. 11,12 Conducting polymers mainly store energy through a faradaic current resulting from the transfer of charge between electrode and electrolyte (pseudocapacitors). The charge-transfer process is usually accompanied by electrosorption, oxidation-reduction reactions, and intercalation processes.13 When oxidation occurs, ions are transferred to the polymer backbone and, in case of reduction, the ions are released back into the solution; therefore, the charge-discharge process in con...

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