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.

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A high-performance Al/graphite battery has been investigated, employing a natural graphite cathode (NG) and 1-ethyl-3methylimidazolium chloride (EMIMCl):AlCl 3 as electrolyte. The employed graphite is characterized by excellent reversibility as revealed by electrochemical tests and ex-situ XRD. The Al/ EMIMCl:AlCl 3 /NG battery showed extraordinary performance in terms of rate capability, and cycle life. The cell delivered a capacity of 110 mAh g À1 at lower current values, retaining 90 % and 60 % of the capacity employing a current of 20 A g À1 and 50 A g À1 , respectively (i. e., a complete charge-discharge cycle in 35 and 9 seconds, respectively). Furthermore, the cycling test performed using a current of 20 A g À1 revealed an extremely long calendar life of half million of cycles. The practical applicability of the investigated Al/graphite system has been ascertained; this involved estimating the energy efficiency as a function of current rate and carefully calculating the practical energy densities that can be obtained from the system.

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This paper presents a Review on the development of thin‐film (all‐solid‐state) Li‐ion microbatteries. The need to move from 2D to 3D configurations, the ever‐increasing necessity to adopt Li‐ion or rocking‐chair technology in microbatteries, and the development of new processing techniques and materials are discussed. Materials based on TiO2 are very promising as negative electrodes for Li‐ion microbatteries. Strong emphasis is placed on the possibility of utilising TiO2, especially self‐supported nanotubular TiO2, as an anode material for commercial 2D or 3D Li‐ion microbatteries. The use of TiO2 is ecologically and economically competitive and provides cells with low self‐discharge while eliminating the risk of overcharging due to its relatively high operating voltage. The high operating voltage of TiO2 also presents the advantage of negligible electrolyte decomposition. Each polymorphic form of TiO2 (anatase, rutile, TiO2(B), or brookite) has an attractive lithium storage behaviour, especially, when nanostructured. Owing to their remarkable nanoarchitecture, TiO2 nanotubes grown by potentiostatic anodization, and their derivatives (cation‐ or anion‐doped and hierarchical composites with nanostructured metals or metal oxides), deserve attention for the fabrication of 2D or 3D Li‐ion microbatteries.

The highly conformal electrodeposition of a copolymer electrolyte (PMMA-PEO) into self-organized titania nanotubes (TiO2nt) is reported. The morphological analysis carried out by scanning electron microscopy and transmission electron microscopy evidenced the formation of a 3D nanostructure consisting of a copolymer-embedded TiO2nt. The thickness of the copolymer layer can be accurately controlled by monitoring the electropolymerization parameters. X-ray photoelectron spectroscopy measurements confirmed that bis(trifluoromethanesulfone)imide salt was successfully incorporated into the copolymer electrolyte during the deposition process. These results are crucial to fabricate a 3D Li-ion power source at the micrometer scale using TiO2nt as the negative electrode.

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