Abstract
Magnesium batteries are a promising technology for a new generation of energy storage for portable devices. Attention should be paid to electrolyte and electrode material development in order to develop rechargeable Mg batteries. In this study, we report the use of the spinel lithium titanate or Li4Ti5O12 (LTO) as an active electrode for Mg2+-ion batteries. The theoretical capacity of LTO is 175 mA h g−1, which is equivalent to an insertion reaction with 1.5 Mg2+ ions. The ability to enhance the specific capacity of LTO is of practical importance. We have observed that it is possible to increase the capacity up to 290 mA h g−1 in first discharge, which corresponds to the reaction with 2.5 Mg2+ ions. The addition of MgCl2·6H2O to the electrolyte solutions significantly improves their electrochemical performance and enables reversible Mg deposition. Ex-situ X-ray diffraction (XRD) patterns reveal little structural changes, while X-ray photoelectron spectrometer (XPS) (XPS) measurements suggest Mg reacts with LTO. The Ti3+/Ti4+ ratio increases with the amount of inserted magnesium. The impedance spectra show the presence of a semicircle at medium-low frequencies, ascribable to Mg2+ ion diffusion between the surface film and LTO. Further experimental improvements with exhaustive control of electrodes and electrolytes are necessary to develop the Mg battery with practical application.
Highlights
Magnesium batteries are promising energy storage devices, due to their natural virtues, such as abundance, high theoretical volumetric capacity (3832 mA h cm−3), and operational safety [1,2,3,4,5]
The development of Mg batteries has been blocked by the lack of proper inorganic cathode materials, which commonly suffer from extremely slow kinetics of the insertion of Mg2+ into the intercalation host
Stable and reversible magnesium plating/stripping was reported for Mg(TFSI)2 in dimethoxyethane (DME) and Mg(TFSI)2 in glyme, when MgCl2 or Mg(BH4)2 or anthracene was added [15,16,17]
Summary
Magnesium batteries are promising energy storage devices, due to their natural virtues, such as abundance, high theoretical volumetric capacity (3832 mA h cm−3), and operational safety [1,2,3,4,5]. The electrolyte, composed of magnesium triphenolate borohydride and Mg(TFSI), displays reversible Mg insertion/de-insertion in the Mo6S8 Chevrel cathode phase delivering a capacity value of 94 mA h g−1 and 96% coulombic efficiency, as reported by Hebié et al [17]. In these papers, it is claimed that the electrochemical performance of the TFSI-based electrolyte solutions is governed by their purity level. LTO is a well-known electrode material, with insertion properties useful for Li-ion and Na-ion batteries, that have been already studied [21,22,23,24]. The results, which were obtained by allowing water molecules to remain in the inorganic salt, may be useful in comparing with the results obtained by using the anhydrous salt
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