(Invited) A Rational Design for Batteries at Nanoscale by Atomic Layer Deposition

Abstract

A self-aligned nanostructured battery fully confined within a single nanopore presents a powerful platform to determine the rate performance and cyclability limits of nanostructured storage devices. Atomic layer deposition (ALD) has enabled us to create and evaluate such structures, comprised of nanotubular electrodes and electrolyte confined within anodic aluminum oxide (AAO) nanopores as “all-in-one” nanopore batteries.This nanopore battery displays exceptional power-energy performance and cyclability when tested as massively parallel devices (~2billion/cm2), each with ~1um3 volume (~1fL). [1]The unprecedented thickness and conformality control of ALD and the highly self-aligned nanoporous structure of anodic aluminum oxide (AAO) are essential to enable fabrication of precision, self-aligned, regular nanopore batteries. To realize such structure, we began with fine tuning of ALD process conformality inside high aspect ratio (300:1) AAO nanopores. Ru/Pt metal is optimized to be 15µm deep at both sides of 50µm long AAO pores in order to provide fast electron transport to overlying V2O5 at both anode and cathode sides, while keeping them spatially and electrically isolated. Crystalline V2O5 was deposited as active storage material inside the metal nanotubes using O3 as the oxidant. Then the V2O5 was electrochemically prelithiated at one end to serve as anode while pristine V2O5 without Li at the other end served as cathode, enabling the battery to be cycled between 0.2V and 1.8V. Capacity retention of this full cell is 95% at 5C rate and 46% at 150C, with more than 1000 charge/discharge cycles. Further increase of full cell output potential is also demonstrated for SnO2 and TiO2 anodes in asymmetric full cells with V2O5cathodes. These results demonstrate the promise of ultrasmall, self-aligned/regular, densely packed nanobattery structures as a test bed to study ionics and electrodics at nanoscale with a variety of geometrical modifications and as a building block for high performance energy storage systems. [1] Liu, C.; Gillette, E. I.; Chen, X.; Pearse, A. J.; Kozen, A. C.; Schroeder, M. A.; Gregorczyk, K. E.; Lee, S. B.; Rubloff, G. W., An all-in-one nanopore battery array. Nature Nanotechnology 2014, 9 (12), 1031-1039.