Insights into the Degradation Mechanism of the Magnesium Anode in Magnesium–Chalcogen Batteries: Revealing Principles for Anode Design with a 3D-Structured Magnesium Anode

Magnesium–chalcogen batteries are promising post lithium battery systems for large-scale energy storage applications in terms of energy density, material sustainability, safety, and cost. However, the soluble reaction intermediates, such as polysulfides or polyselenides, formed during the electrochemical processes can severely passivate the Mg metal anode, limiting the cycle life of the batteries. It is necessary to rescrutinize the failure in Mg–chalcogen batteries from an anodic perspective. Herein, the Mg metal anode failure mechanism is thoroughly examined, revealing that it is induced by an inhomogeneous Mg deposition promoted by soluble intermediates from chalcogen cathodes. To further confirm the mechanism and solve this anode failure problem, a multifunctional 3D current collector is used to decrease the local current density and regulate the Mg deposition behavior. The present findings are anticipated to provide guidance for anode design, enhance the life-span of Mg–chalcogen batteries, and facilitate the development of other magnesium metal batteries

A New, Highly Active Bimetallic Grubbs–Hoveyda–Blechert Precatalyst for Alkene Metathesis

A new Grubbs−Hoveyda−Blechert alkene metathesis catalyst, in which the benzylidene ligand has been coordinated to a highly electron-withdrawing tricarbonylchromium moiety, is presented. The structure of the complex provides evidence for a so far unreported attractive interaction between the benzylidene hydrogen atom and one of the mesityl substituents at the Arduengo carbene ligand. Screening of the catalytic properties shows that the activity of the new catalyst in ring-closing, enyne, cross, and homo metathesis of alkenes is comparable and in some cases better than that of known catalysts

Vanadium Oxychloride/Magnesium Electrode Systems for Chloride Ion Batteries

We report a new type of rechargeable chloride ion battery using vanadium oxychloride (VOCl) as cathode and magnesium or magnesium/magnesium chloride (MgCl₂/Mg) as anode, with an emphasis on the VOCl-MgCl₂/Mg full battery. The charge and discharge mechanism of the VOCl cathode has been investigated by X-ray diffraction, X-ray photoelectron spectroscopy, and electrochemical measurements, demonstrating the chloride ion transfer during cycling. The VOCl cathode can deliver a reversible capacity of 101 mAh g^–1 at a current density of 10 mA g^–1 and a capacity of 60 mAh g^–1 was retained after 53 cycles in this first study

A New, Highly Active Bimetallic Grubbs–Hoveyda–Blechert Precatalyst for Alkene Metathesis

A new Grubbs−Hoveyda−Blechert alkene metathesis catalyst, in which the benzylidene ligand has been coordinated to a highly electron-withdrawing tricarbonylchromium moiety, is presented. The structure of the complex provides evidence for a so far unreported attractive interaction between the benzylidene hydrogen atom and one of the mesityl substituents at the Arduengo carbene ligand. Screening of the catalytic properties shows that the activity of the new catalyst in ring-closing, enyne, cross, and homo metathesis of alkenes is comparable and in some cases better than that of known catalysts

Magnesium Anode for Chloride Ion Batteries

A key advantage of chloride ion battery (CIB) is its possibility to use abundant electrode materials that are different from those in Li ion batteries. Mg anode is presented as such a material for the first time and Mg/C composite prepared by ball milling of Mg and carbon black powders or thermally decomposed MgH₂/C composite has been tested as anode for CIB. The electrochemical performance of FeOCl/Mg and BiOCl/Mg was investigated, demonstrating the feasibility of using Mg as anode

Operando UV/vis Spectroscopy Providing Insights into the Sulfur and Polysulfide Dissolution in Magnesium–Sulfur Batteries

The magnesium–sulfur battery represents a promising post-lithium system with potentially high energy density and improved safety. However, just as all metal–sulfur systems, it is plagued with the polysulfide shuttle leading to active material loss and surface layer formation on the anode. To gain further insights, the present study aims to shed light on the dissolution characteristics of sulfur and polysulfides in glyme-based electrolytes for magnesium–sulfur batteries. Therefore, operando UV/vis spectroscopy and imaging were applied to survey their concentration in solution and the separator coloration during galvanostatic cycling. The influence of conductive cathode additives (carbon black and titanium nitride) on the sulfur retention and cycling overpotentials were investigated. Thus, valuable insights into the system’s reversibility and the benefit of additional reaction sites are gained. On the basis of these findings, a reduction pathway is proposed with S8, S62–, and S42– being the present species in the electrolyte, while the dissolution of S82– and S3•– is unfavored. In addition, the evolution of the sulfur species concentration during an extended rest at open-circuit voltage was investigated, which revealed a three-staged self-discharge

Magnesium Anode Protection by an Organic Artificial Solid Electrolyte Interphase for Magnesium-Sulfur Batteries

In the search for post-lithium battery systems, magnesium–sulfur batteries have attracted research attention in recent years due to their high potential energy density, raw material abundance, and low cost. Despite significant progress, the system still lacks cycling stability mainly associated with the ongoing parasitic reduction of sulfur at the anode surface, resulting in the loss of active materials and passivating surface layer formation on the anode. In addition to sulfur retention approaches on the cathode side, the protection of the reductive anode surface by an artificial solid electrolyte interphase (SEI) represents a promising approach, which contrarily does not impede the sulfur cathode kinetics. In this study, an organic coating approach based on ionomers and polymers is pursued to combine the desired properties of mechanical flexibility and high ionic conductivity while enabling a facile and energy-efficient preparation. Despite exhibiting higher polarization overpotentials in Mg–Mg cells, the charge overpotential in Mg–S cells was decreased by the coated anodes with the initial Coulombic efficiency being significantly increased. Consequently, the discharge capacity after 300 cycles applying an Aquivion/PVDF-coated Mg anode was twice that of a pristine Mg anode, indicating effective polysulfide repulsion from the Mg surface by the artificial SEI. This was backed by operando imaging during long-term OCV revealing a non-colored separator, i.e. mitigated self-discharge. While SEM, AFM, IR and XPS were applied to gain further insights into the surface morphology and composition, scalable coating techniques were investigated in addition to ensure practical relevance. Remarkably therein, the Mg anode preparation and all surface coatings were prepared under ambient conditions, which facilitates future electrode and cell assembly. Overall, this study highlights the important role of Mg anode coatings to improve the electrochemical performance of magnesium–sulfur batteries

LiBH₄−Mg(BH₄)₂: A Physical Mixture of Metal Borohydrides as Hydrogen Storage Material

The LiBH4−Mg(BH4)2 system has been investigated as a possible hydrogen storage material. Several composites were synthesized by ball milling, namely, xLiBH4−(1−x)Mg(BH4)2 with x = 0, 0.10, 0.25, 0.33, 0.40, 0.50, 0.60, 0.66, 0.75, 0.80, 0.90, 1. The physical mixture was investigated by using X- ray powder diffraction and thermal analysis. Interestingly, already a small amount of LiBH4 makes the α to β transition of Mg(BH4)2 reversible, which has not been reported before. The eutectic composition was found to exist at 0.50 x x = 0.50 composite releases about 7.0 wt % of hydrogen

Long-Cycle-Life Calcium Battery with a High-Capacity Conversion Cathode Enabled by a Ca²⁺/Li⁺ Hybrid Electrolyte

Calcium (Ca) batteries represent an attractive option for electrochemical energy storage due to physicochemical and economic reasons. The standard reduction potential of Ca (−2.87 V) is close to Li and promises a wide voltage window for Ca full batteries, while the high abundance of Ca in the earth’s crust implicates low material costs. However, the development of Ca batteries is currently hindered by technical issues such as the lack of compatible electrolytes for reversible Ca2+ plating/stripping and high-capacity cathodes with fast kinetics. Herein, we employed FeS2 as a conversion cathode material and combined it with a Li+/Ca2+ hybrid electrolyte for Ca batteries. We demonstrate that Li+ ions ensured reversible Ca2+ plating/stripping on the Ca metal anode with a small overpotential. At the same time, they enable the conversion of FeS2, offering high discharge capacity. As a result, the Ca/FeS2 cell demonstrated an excellent long-term cycling performance with a high discharge capacity of 303 mAh g–1 over 200 cycles. Even though the practical application of such an approach is questionable due to the high quantity of electrolytes, we believe that our scientific findings still provide new directions for studying Ca batteries with long-term cycling

Toward Highly Reversible Magnesium–Sulfur Batteries with Efficient and Practical Mg[B(hfip)₄]₂ Electrolyte

The rechargeable magnesium (Mg) battery has been considered a promising candidate for future battery generations due to unique advantages of the Mg metal anode. The combination of Mg with a sulfur cathode is one of the attractive electrochemical energy storage systems that use safe, low-cost, and sustainable materials and could potentially provide a high energy density. To develop a suitable electrolyte remains the key challenge for realization of a magnesium sulfur (Mg–S) battery. Herein, we demonstrate that magnesium tetrakis­(hexafluoroisopropyloxy) borate Mg­[B­(hfip)₄]₂ (hfip = OC­(H)­(CF₃)₂) satisfies a multitude of requirements for an efficient and practical electrolyte, including high anodic stability (>4.5 V), high ionic conductivity (∼11 mS cm^–1), and excellent long-term Mg cycling stability with a low polarization. Insightful mechanistic studies verify the reversible redox processes of Mg–S chemistry by utilizing Mg­[B­(hfip)₄]₂ electroylte and also unveil the origin of the voltage hysteresis in Mg–S batteries