Abstract
Achieving the full potential of magnesium-ion batteries (MIBs) is still a challenge due to the lack of adequate electrodes or electrolytes. Grignard-based electrolytes show excellent Mg plating/stripping, but their incompatibility with oxide cathodes restricts their use. Conventional electrolytes like bis(trifluoromethanesulfonyl)imide ((Mg(TFSI)2) solutions are incompatible with Mg metal, which hinders their application in high-energy Mg batteries. In this regard, alloys can be game changers. The insertion/extraction of Mg2+ in alloys is possible in conventional electrolytes, suggesting the absence of a passivation layer or the formation of a conductive surface layer. Yet, the role and influence of this layer on the alloys performance have been studied only scarcely. To evaluate the reactivity of alloys, we studied InSb as a model material. Ex situ X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy were used to investigate the surface behavior of InSb in both Grignard and conventional Mg(TFSI)2/DME electrolytes. For the Grignard electrolyte, we discovered an intrinsic instability of both solvent and salt against InSb. XPS showed the formation of a thick surface layer consisting of hydrocarbon species and degradation products from the solvent (THF) and salt (C2H5MgCl−(C2H5)2AlCl). On the contrary, this study highlighted the stability of InSb in Mg(TFSI)2 electrolyte.
Highlights
Nowadays, lithium-ion batteries (LIBs) are the main power source for portable applications due to their high energy and power density [1]
Surface Layer Composition in a Mg(TFSI)2-Based Electrolyte To compare the reactivity of the alloy compound in the Grignard electrolyte with a conventional electrolyte, we investigated the surface layer formed on a InSb electrode cycled in a Mg(TFSI)2-based electrolyte
We investigated with ex situ X-ray photoelectron spectroscopy (XPS) the surface reactivity of the InSb material at different stages of cycling in two different electrolytes for Mg batteries
Summary
Lithium-ion batteries (LIBs) are the main power source for portable applications due to their high energy and power density [1]. The electrochemical storage technology based on magnesium ion transport emerged as a promising candidate for post-lithium systems. Magnesium is an excellent alternative to lithium due to its high specific capacity, low cost, abundance on Earth, and low reactivity. The main bottleneck for the development of Mg-based technologies is the lack of a suitable electrolyte allowing both reversible Mg electrodeposition at the anode and reversible cation insertion in cathode materials at high potential. A blocking passivation layer forms that prevents Mg2+ ion migration [14,15] To address this issue, several strategies are being employed, most of them towards developing advanced electrolytes with wide electrochemical stability window and high ionic conductivity [16,17,18,19,20]. An adequate electrolyte compatible with both Mg anode and high-potential cathode is yet to be found
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