Abstract
The potential for low cost, environmentally friendly and high rate energy storage has led to the study of anatase-TiO2 as an electrode material in aqueous Al3+ electrolytes. This paper describes the improved performance from an electrochemically treated composite TiO2 electrode for use in aqueous Al-ion batteries. After application of the cathodic electrochemical treatment in 1 mol/dm3 KOH, Mott–Schottky analysis showed the treated electrode as having an increased electron density and an altered open circuit potential, which remained stable throughout cycling. The cathodic treatment also resulted in a change in colour of TiO2. Treated-TiO2 demonstrated improved capacity, coulombic efficiency and stability when galvanostatically cycled in 1 mol·dm−3AlCl3/1 mol·dm−3 KCl. A treated-TiO2 electrode produced a capacity of 15.3 mA·h·g−1 with 99.95% coulombic efficiency at the high specific current of 10 A/g. Additionally, X-ray diffraction, scanning electron microscopy and X-ray photoelectron spectroscopy were employed to elucidate the origin of this improved performance.
Highlights
Aqueous intercalation batteries are being explored as potentially cheap, safe, non-toxic and high power energy storage devices [1,2,3,4]
Other insertion materials with a suitably negative potential range in aqueous electrolytes, excluding those based on lithium salts, are limited to Nasicon titanium phosphates and vanadium oxides, while activated carbon has been employed as a capacitive negative electrode [12,13,14,15]
The colour change of a TiO2 electrode from white to pale yellow suggests the introduction of Ti3+, though this could not be confirmed with XPS measurements
Summary
Aqueous intercalation batteries are being explored as potentially cheap, safe, non-toxic and high power energy storage devices [1,2,3,4]. To date there has been limited discussion of the low coulombic efficiency of anatase TiO2 in aqueous aluminium salt electrolytes, especially during initial cycles This is an important point for the electrode to be considered for use in full, two electrode battery. 150 mA·h·g−1 was measured from TiO2 nanospheres at the low specific current of 50.25 mA/g, while a graphene-TiO2 electrode produced a discharge capacity of ca. TiO2 nanotube arrays has shown improved electrochemical performance as aqueous supercapacitor current collectors, while self-doped TiO2 nano structures have demonstrated improved photocatalytic activity for water splitting [27,28]. We report that this safe, facile and repeatable reduction treatment can be applied to composite TiO2 electrodes in order to improve their performance as a negative electrode in aqueous AlCl3 electrolyte, demonstrating high rate capability and stability during cycling. Doping of TiO2 is demonstrated to be an important factor for improving coulombic efficiency and initial cycling stability in aqueous electrolyte
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