Coaxial Nanotube Battery inside Single Nanopore

We report here a nanobattery comprised of nanotubular electrodes and electrolyte confined within an anodic aluminum oxide (AAO) nanopore. To construct confined electrically insulating electrolyte space in batteries with aligned nanoelectrodes, we have used atomic layer deposition (ALD) to synthesize nanotubular, heterogeneous coaxial electrodes at both ends of AAO nanopores. The nanoelectrodes include Ru nanotube current collectors with V₂O₅storage material on top of the Ru to form a symmetric full storage cell, with anode and cathode separated by an electrolyte region.  

The V₂O₅ is prelithiated at one end to serve as anode while pristine V₂O₅ at the other end serves as cathode, so that the battery can be asymmetrically cycling between 0.2V and 1.8V. Capacity retention at high power (relative to 1C values 178mAh/g) is 95% at 5C and 46% at 150C. At 5C rate (12 min charge-discharge cycle), 81.3% capacity remains after 1000 cycles. The importance of incorporating integrated current collectors is demonstrated by the rate performance of V₂O₅ cathode with Ru nanotube current collector as compared to a Au planar current collector. While both show similar capacity at low rate (1C),  at high rates (150C) that demand fast electron transport the V₂O₅/Ru nanotube (78mAh/g) exhibits almost twice the capacity of the V₂O₅/planar Au (42mAh/g). 

This nanopore battery poses an extreme case of highly confined organic electrolyte environments in ultrasmall batteries.  These promising results demonstrate the importance of integrating current collectors with storage nanoelectrodes, the benefit of electrolyte-accessible surface area of the nanotubular electrodes, and the cycling robustness of the nanostructures. At the same time, they provide a valuable data source for fundamental modeling to understand and quantify a science of “nanoionics” – a mesoscale phenomenon resulting from dense packing of ion storage nanostructures.