Nowadays, millimeter scale power sources are key devices for providing autonomy to smart, connected and miniaturized sensors. However, until now, planar solid state microbatteries do not yet exhibit a sufficient surface energy density. In that context, architectured 3D (3 dimensional) microbatteries appear therefore to be a good solution to improve the material mass loading while keeping small the footprint area. Beside the design itself of the 3D microbaterry, one important technological barrier to address is the conformal deposition of thin films (lithiated or not) on 3D structures. For that purpose, Atomic Layer Deposition (ALD) technology is a powerful technique that enable conformal coatings of thin film on complex substrate. In this paper, an original, robust and highly efficient 3D scaffold is proposed to significantly improve the geometrical surface of miniaturized 3D microbattery.Four functional layers composing the 3D lithium ion microbattery stacking has been Received: ((will be filled in by the editorial staff))Revised: ((will be filled in by the editorial staff))
Smart integrated miniaturized microsystems require harvesting and storage power sources in order to be autonomous. From the energy point of view, commercially available lithium-ion microbatteries with planar topology do not have suffi cient performance to address the challenging autonomy of microsystems. In aiming for this goal, new concepts based on 3D topologies have been published [ 1 ] in last ten years. By developing a 3D topology, the surface area, and thus the capacity, of the device is increased. The fabrication of high-surfacecapacity devices at the microscale is performed by 1) nano-/micro-structuring a substrate and 2) making a conformal deposition of an electrochemically active thin fi lm on the 3D topology. To achieve conformal deposition on steps and other 3D features, electrodeposition (ED) or highvacuum atomic layer deposition (ALD) are required. The gain obtained with the 3D topology is referred to as the ratio between the 3D and 2D surface areas, and it is known as the area enlargement factor (AEF). The energy density is drastically increased in the 3D topology compared to the planar topology. The power density is also enhanced because the thickness of the 3D deposited material is kept relatively low; the diffusion length of the lithium ions inside the electrode material is reduced, leading to an increase in the charge/discharge rate of the 3D microstorage device.Interdigitated 3D lithium-ion microbatteries based on carbon micro-electromechanical system (C-MEMS) technology with a surface capacity close to 125 µA h cm -2 have been reported [ 2,3 ] by Dunn and co-workers. The micromachining of silicon or glass substrates has been performed by the Peled group [ 4,5 ] in order to fabricate a liquid-based 3D lithium-ion microbattery. Microcontainers fi lled with the battery materials have reached 1 mA h cm -2 under 2 V; the exacerbated surface capacity is clearly enhanced due to the 3D topology. Recently, an interdigitated lithium-ion microbattery based on porous electrodes has been reported with power and energy capabilities greatly enhanced by the 3D porous network. [ 6 ] Simon and co-workers [ 7 ] have developed a nano-architectured aluminum-based 3D metallic current-collector; on top of the 3D nanostructure, a thin layer of anatase TiO 2 polymorph was deposited by ALD. An AEF of 10 is exhibited between the measured 2D and 3D surface capacity. An interesting concept using top-down and bottom-up approaches has been published by Gerasopoulos et al. [ 8 ] using low-aspectratio gold micropillars decorated with biological nano-objects (tobacco mosaic virus, TMV); an enhancement of the surface capacity of a V 2 O 5 thin fi lm deposited by ALD was demonstrated using this novel structure. Previously, Gerasopoulos [ 9 ] et al. reported the ALD of TiO 2 onto biological scaffolds composed of TMV. The TMV nanostructures had been covered beforehand by a nickel conductive layer. The bio-templating approach [ 10 ] has also been used by Kim et al. to fabricate a TiO 2 3D nanonetwork based on peptide assembly; a h...
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