A Computational Study of a Single-Walled Carbon-Nanotube-Based Ultrafast High-Capacity Aluminum Battery

Abstract

Exploring suitable electrode materials is a fundamental step toward developing Al batteries with enhanced performance. In this work, we explore using density functional theory calculations the feasibility of single-walled carbon nanotubes (SWNTs) as a cathode material for Al batteries. Carbon nanotubes with hollow structures and large surface area are able to overcome the difficulty of activating the opening of interlayer spaces as observed in graphite electrode during the first intercalation cycle. Our results show that AlCl₄ binds strongly with the SWNT to result in an energetically and thermally stable AlCl₄ -adsorbed SWNT system. Diffusion calculations show that the SWNT system allows ultrafast diffusion of AlCl₄ with a more favorable inner surface diffusion than outer surface diffusion. Our charge-density difference and Bader atomic charge analysis confirm the oxidation of SWNT upon adsorption of AlCl₄ , which shows a similar behavior to the previously studied graphite cathode. The average open-circuit voltage and AlCl₄ storage capacity increases with increasing SWNT diameter and can be as high as 1.96 V and 275 mA h g^-1 in (25,25) SWNT relative to graphite (70 mA h g^-1 ). All of these properties show that SWNTs are a potential cathode material for high-performance Al batteries and should be explored further.

Keywords: aluminum; carbon; density functional calculations; electrochemistry; nanotubes.