Mg batteries are a promising battery technology that could lead to safer and significantly less expensive non-aqueous batteries with energy densities comparable or even better than state-of-the-art Li-ion batteries. Although the first prototype Mg battery using stable Mo6S8 as cathode was introduced over fifteen years ago, major challenges remain to be solved. In particular, the design of high energy cathode materials and the development of non-corrosive electrolytes with high oxidative stability are issues that need to be tackled. Herein, we present a new, general, and robust approach towards achieving stable cycling of Mg batteries. The core of our approach is the use of stable polymer cathode and Mg powder anode coupled with non-nucleophilic electrolytes. Our systems exhibit an excellent rate capability and significant improvement in electrochemical stability.

Magnesium−sulfur batteries are considered as attractive energystorage devices due to the abundance of electrochemically active materials and high theoretical energy density. Here we report the mechanism of a Mg−S battery operation, which was studied in the presence of simple and commercially available salts dissolved in a mixture of glymes. The electrolyte offers high sulfur conversion into MgS in the first discharge with low polarization. The electrochemical conversion of sulfur with magnesium proceeds through two well-defined plateaus, which correspond to the equilibrium between sulfur and polysulfides (high-voltage plateau) and polysulfides and MgS (low-voltage plateau). As shown by XANES, RIXS (resonant inelastic X-ray scattering), and NMR studies, the end discharge phase involves MgS with Mg atoms in a tetrahedral environment resembling the wurtzite structure, while chemically synthesized MgS crystallizes in the rock-salt structure with octahedral coordination of magnesium.

A comprehensive study is reported entailing a comparison of Li, Na, K, Mg, and Ca based electrolytes and an investigation of the reliability of electrochemical tests using half-cells. Ionic conductivity, viscosity, and Raman spectroscopy results point to the cationsolvent interaction to follow the polarizing power of the cations, i.e. Mg 2+ > Ca 2+ > Li + > Na + > K + and to divalent cation based electrolytes having stronger tendency to form ion pairs -lowering the cation accessibility and mobility. Both increased temperature and the use of anions with delocalized negative charge, such as TFSI, are effective in mitigating this issue. Another factor impeding the divalent cations mobility is the larger solvation shells, as compared to those of monovalent cations, that in conjunction with stronger solvent -cation interactions contribute to slower charge transfer and ultimately a large impedance of Mg and Ca electrodes. An important consequence is the non-reliability of the pseudo-reference electrodes as these present both significant potential shifts as well as unstable behaviors. Finally, experimental protocols in order to achieve consistent results when using half-cell set-ups are Although the lithium-ion battery is currently being considered as the most promising technology for electric vehicle propulsion, the development of alternative and complementary battery chemistries and technologies is of great importance, especially aiming at large-scale applications, i.e. the grid for which the cost in $/kWh and sustainability are crucial indicators. Indeed, the implementation of lithium based technology at large scale faces a significant challenge, since the controversial debates on lithium availability and cost cannot be overlooked. Amongst several chemistries possible the most appealing alternatives involve the use of sodium (Na), magnesium (Mg) or calcium (Ca) for mainly two reasons. The prime is the abundance of the raw materials, i.e. Na, Mg, and Ca being the 6 th , 8 th , and 5 th most abundant elements in the Earth's crust, vs. 25 th for Li, making them 20 to 50 times cheaper than Li, e.g. $5000/ton, $135-165/ton, $265/ton, and $100/ton for Li 2 CO 3 , Na 2 CO 3 , MgO 2 , and CaCO 3 , 1 respectively. Performance wise, the low cost alternatives of Na, Mg, and Ca technologies would also benefit from high standard reduction potentials, ca. −2.71, −2.37, and −2.87 V vs. SHE for Na, Mg, and Ca, respectively, as compared to −3.04 V for Li, and large theoretical electrochemical capacities, both gravimetric and volumetric, for the metal electrodes (Fig. 1).Sodium metal anodes are already used in the liquid state (m.p. ∼97• C) in the Na/S technology 2 and room-temperature Na-ion technology is currently intensively investigated with hundreds of papers appearing per year, with progress being summarized in several review papers amongst which 3-5 are the most recent. For Mg and Ca metal anodes, the situation is radically different. For the Mg battery technology, proof-of-concept was achieved as late as in 2000, 6 although i...

The impact of the solid film deposit (mainly Li2S) on the complex electrochemistry of a Li–S cell is studied in detail. Already a simple, straightforward experiment strongly indicates that this impact might be much smaller than usually assumed. Notably, a similar phenomenon is demonstrated for another battery operated on the same basic principle: the magnesium–sulfur battery. In order to better detect the surface-specific phenomena associated with formation and properties of the solid surface deposit, we construct special electrochemical cells with a flat glassy carbon disc or other well-defined materials. Different model systems are prepared in which crucial variables such as the electrode configuration, separator type, and state of charge are varied in a systematic and controlled way. Electrochemical results are supplemented with data from microstructural analysis, in particular focused ion beam–scanning electron microscopy (FIB-SEM) imaging and X-ray diffraction analysis. We show that the growth of the surface film is more complex than generally assumed and that its defect-rich morphology hardly represents any obstacle for electrochemical reaction(s) to take place. Rather, the cell operation is limited by diffusional processes and depletion of polysulfide concentration in electrolyte. The new insight into the occurrence, properties, and especially the impact of solid film deposits on operation of the Li–S system is expected to have important implications for future design of Li–S practical cells.

Organic materials are receiving an increasing amount of attention as electrode materials for future post lithium-ion batteries due to their versatility and sustainability. However, their electrochemical reaction mechanism has seldom been investigated. This is a direct consequence of a lack of straightforward and broadly available analytical techniques. Herein, a straightforward in operando attenuated total reflectance infrared spectroscopy method is developed that allows visualization of changes of all infrared active bands that occur as a consequence of reduction/oxidation processes. In operando infrared spectroscopy is applied to the analysis of three different organic polymer materials in lithium batteries. Moreover, this in operando method is further extended to investigation of redox reaction mechanism of poly(anthraquinonyl sulfide) in a magnesium battery, where a reduction of carbonyl bond is demonstrated as a mechanism of electrochemical activity. Conclusions done by the in operando results are complemented by synthesis of model compound and density functional theory calculation of infrared spectra.