(Invited) Nanopore Batteries: Fast and Slow Ion Transport in 1D and 3D Networked Porous Nanostructure Electrodes
Authors: Lee Sang Bok 
Published: February 2020

While interest in nanostructured materials for batteries has been growing enormously in recent years, limited systematic studies have been carried out on controlled architectures to explore the impact of structure on ion transport and resulting charge-discharge rate performance in these electrodes. Here we utilize a combination of well-defined porous 1D and 3D networked nanostructures and atomic layer deposition to fabricate a variety of systematically variable electrode architectures and describe a systematic study from 1D array electrode to 3D electrode. The structural control and electrode design are described in detail. Then, analysis of the rate performance, with a focus on distinguishing between diffusion and charge transfer limited reaction mechanisms, is carried out for two distinct electrode systems, focusing on different issues which face advanced electrode architectures. First, we study a quantitative understanding of 1D nanopore battery electrode’s superior power performance – fast electrochemistry through surface-dominant Li ion insertion. The kinetics of the charge storage reaction strongly influences high power characteristic of the electrode materials. An asymmetric nanopore battery was also fabricated to give higher energy storage. Second, we analyze the impact of transitioning from 1D to 3D structured electrodes. The traditional straight porous AAO films are fabricated for 1D nanotube array and interconnected pores 3D interconnected nanotube array electrode structures. Nanostructured V2O5 electrodes in the nanopores were examined for Li ion batteries as it is one of the well characterized cathode material. V2O5 can reversibly accommodate up to two Li ions. When V2O5 was cycled within the one Li insertion window, the 3D interconnected nanotubular structure showed superior power capabilities over the 1D nanotubular array. With the two Li ion insertion window, an opposite trend was observed, with interconnected electrode performing worse. As the structure between the one and two Li insertion windows were kept constant, possible hypothesis and explanation will be discussed through a dramatic change of V2O5 electrical and electrochemical properties. Up to one lithiation, the conductivity of the material slightly increases whereas with the second lithiation the conductivity dramatically drops by two orders of magnitude due to the disruption in the electron conduction mechanism. In the interconnected electrode, with one Li insertion, the conductivity of the electrode near the current collector increases with the degree of lithiation allowing better usage of the material farther away from the current collector due to lower ohmic loss of the overpotential needed. However, with two Li insertion the conductivity drops near the current collector which prevents the utilization of the material farther away resulting in lower power performance. This study opens up opportunities for rationally designed advanced electrode architectures to optimize the performance of electrochemical energy storage devices in the future.