Electrochemical study of TiO2 in aqueous AlCl3 electrolyte via vacuum impregnation for superior high-rate electrode performance

A W Holland,R G A Wills,A Hector,A Cruden,A Zerey

doi:10.1186/s42500-019-0010-9

Abstract

This communication elucidates the charge storage mechanism of a TiO2 electrode in 1 mol dm− 3 AlCl3 for use in aqueous-ion batteries. Cyclic voltammetry studies suggest a surface contribution to charge storage and that cycle life can be improved by limiting the potential ≥ − 1.0 V vs SCE. In order to enhance this surface contribution, a simple vacuum impregnation technique was employed to improve electrode-electrolyte contact. This resulted in a significant improvement in the high rate performance of TiO2, where a capacity of 15 mA h g− 1 was maintained at the very high specific current of 40 A g− 1, a decrease of only 25% from when the electrode was cycled at 1 A g− 1. The vacuum impregnation process was also applied to copper-hexacyanoferrate, envisaged as a possible positive electrode, again resulting in significant improvements to high-rate performance. This demonstrates the potential for using this simple technique for improving electrode performance in other aqueous electrolyte battery systems.

Highlights

Asymmetric and hybrid devices based on a combination of capacitive, psuedocapacitive or battery intercalation electrodes have gained interest lately due to performance characteristics that could bridge the gap between the high energy density of Li-ion chemistries and high power of supercapacitors
TiO2 provides a possible option for a negative electrode, having been studied in aqueous aluminium salt electrolytes and shown to have working potentials lower than ca. < − 0.5 V vs saturated calomel electrode (SCE) [15,16,17,18,19,20], presenting the opportunity for dual-ion devices working at higher voltages [21,22,23,24]
Analysis of the CV response from TiO2 at different scan rates suggested the contribution of a surface controlled charge storage mechanism

Summary

Introduction

Asymmetric and hybrid devices based on a combination of capacitive, psuedocapacitive or battery intercalation electrodes have gained interest lately due to performance characteristics that could bridge the gap between the high energy density of Li-ion chemistries and high power of supercapacitors. Capacitive or surface contributions to charge storage cannot be entirely ruled out, especially at high rates. A graphene incorporated TiO2 electrode studied by Lahan et al, provided a capacity of approximately 20 mA h g− 1 at 6.25 A g− 1, though the electrode showed very limited redox peaks during CV scans, suggesting the possibility of a capacitive or psuedocapacitive mechanism [1]. Previous work has shown high rate capability, up to 360 C (7.2 A g− 1), from commercial TiO2 nanopowders, though relatively low capacities were measured [25]. This communication elucidates the charge storage mechanism of commercial TiO2 powder electrodes in 1 mol dm− 3 AlCl3 and demonstrates a TiO2 electrode capable of stable cycling at 40.0 A g− 1 with close to 100% charge efficiency

Experimental procedures

Results and discussion

Conclusions