An essential requirement for electrolytes in rechargeable magnesium-ion (Mg-ion) batteries is to enable Mg plating−stripping with low overpotential and high Coulombic efficiency. To date, the influence of the Mg/ electrolyte interphase on plating and stripping behaviors is still not well understood. In this study, we investigate the Mg/ electrolyte interphase from electrolytes based on two Mg salts with weakly coordinating anions: magnesium monocarborane ( M g ( C B 1 1 H 1 2 ) 2 ) a n d m a g n e s i u m b i s -(trifluoromethanesulfonyl)imide (Mg(TFSI) 2 ). Cyclic voltammetry and chronopotentiometry of Mg plating−stripping demonstrate significantly lower overpotential in the Mg-(CB 11 H 12 ) 2 electrolyte than in Mg(TFSI) 2 under the same condition. Surface characterizations including X-ray photoelectron spectroscopy and scanning electron microscopy clearly demonstrate the superior chemical and electrochemical stability of the Mg(CB 11 H 12 ) 2 electrolyte at the Mg surface without noticeable interphase formation. On the other hand, characterizations of the Mg/electrolyte interface in the Mg(TFSI) 2 electrolyte indicate the formation of magnesium oxide, magnesium sulfide, and magnesium fluoride as the interfacial compounds resulting from the decomposition of TFSI − anions because of both chemical reduction by Mg and cathodic reduction during Mg deposition.

The synthesis and application of the first high voltage, non-corrosive, Mg battery electrolyte based on small carborane anions are reported. This electrolyte displays equal oxidative stability compared to its larger 12-vertex cousin, but is more cost effective to prepare.

Rechargeable aluminum−sulfur (Al−S) batteries have recently garnered significant interest to the low cost, earth abundance, safety, and high theoretical capacity of the electrode materials. However, Al−S batteries exhibit many challenges that plague other metal−sulfur battery systems, including significant capacity fade of the sulfur electrode due to the formation of electrolyte-soluble reaction intermediates. Here, Al−S cells using chloroaluminate-containing ionic liquid electrolytes were investigated up from the molecular level using multidimensional solid-state 27 Al MAS NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical measurements. Solid-state 27 Al single-pulse NMR measurements acquired on cycled sulfur electrodes containing electrolyte-soaked separator revealed multiple discharge products, which were distinguished into liquid-and solid-phase products based on 27 Al chemical exchange and nutation NMR experiments. During discharge, electrolyte-soluble sulfide species form that coordinate with the AlCl 4 − chloroaluminate anions, resulting in (S x AlCl 4 ) y− electrolyte complexes. These electrolyte-coordinated sulfide species persist upon charge, resulting in the loss of active mass that explains the significant capacity fade observed upon galvanostatic cycling. XPS, XRD, and solid-state 27 Al NMR measurements reveal that solid amorphous Al 2 S 3 forms reversibly upon discharge. The results highlight the technological importance of understanding how electrolyte-soluble sulfide species coordinate with the complex electroactive species used in multivalent metal−sulfur batteries, which can affect their reversibility and electrochemical properties.

No abstract

Rechargeable aluminum metal batteries are an emerging energy storage technology with great promise: aluminum has among the highest capacities of common metal electrodes and is low cost, earth abundant, environmentally friendly, and inherently safe. Despite these opportunities, their technological development has been hindered due to fundamental challenges associated with aluminum electrochemistry. Few electrolytes enable the reversible electrodeposition of aluminum metal at room temperature, while few positive electrode materials have been demonstrated that exhibit high energy density and cycle life in those electrolytes. Here, recent progress will be discussed in the development and characterization of positive electrode materials for rechargeable aluminum metal batteries, including graphites, organic materials, sulfur, and crystalline transition metal compounds. Molecular-scale understanding of their charge storage mechanisms will be elucidated, revealed by a combination of electrochemical, spectroscopic, diffraction, imaging, and theoretical methods, such as multi-dimensional solid-state nuclear magnetic resonance (NMR) spectroscopy, in operando X-ray diffraction (XRD), electron microscopy, and density functional theory (DFT). The diversity of electrochemical charge storage mechanisms possible for aluminum battery chemistries will be highlighted. Overall, the results are aimed at developing next-generation rechargeable aluminum metal batteries for diverse energy storage applications.