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

New Insight into Desodiation/Sodiation Mechanism of MoS₂: Sodium Insertion in Amorphous Mo–S Clusters

Molybdenum disulfide (MoS2) is a promising anode material for sodium batteries due to its high theoretical capacity. While significantly improved electrochemical performance has been achieved, the reaction mechanism is still equivocal. Herein, we applied electron pair distribution function and X-ray absorption spectroscopy to investigate the desodiation/sodiation mechanism of MoS2 electrodes. The results reveal that Mo–S bonds are well preserved and dominant in the sodiation product matrix but do not convert to metallic Mo and Na2S even at deep sodiation. The MoS2 multilayer sheets break into disordered MoSx clusters with modified octahedral symmetry during discharging. The long-range order was not rebuilt during subsequent charging but with partial recovery of the Mo–S coordination symmetry. The mechanism of the reaction is independent of the carbon matrix, although it prevents the MoSx clusters from leaching into the electrolyte and thus contributes to an extended cycle life. This work refreshes the fundamental understanding of the desodiation/sodiation mechanism of MoS2 materials

Surface Modification of Bacterial Cellulose Aerogels’ Web-like Skeleton for Oil/Water Separation

The cellulose nanofibers of bacterial cellulose aerogel (BCA) are modified only on their surfaces using a trimethylsilylation reaction with trimethyichlorosilane in liquid phase followed by freeze-drying. The obtained hydrophobic bacterial cellulose aerogels (HBCAs) exhibit low density (≤6.77 mg/cm³), high surface area (≥169.1 m²/g), and high porosity (≈ 99.6%), which are nearly the same as those of BCA owing to the low degrees of substitution (≤0.132). Because the surface energy of cellulose nanofibers decreased and the three-dimensional web-like microstructure, which was comprised of ultrathin (20–80 nm) cellulose nanofibers, is maintained during the trimethylsilylation process, the HBCAs have hydrophobic and oleophilic properties (water/air contact angle as high as 146.5°) that endow them with excellent selectivity for oil adsorption from water. The HBCAs are able to collect a wide range of organic solvents and oils with absorption capacities up to 185 g/g, which depends on the density of the liquids. Hence, the HBCAs are wonderful candidates for oil absorbents to clean oil spills in the marine environment. This work provides a different way to multifunctionalize cellulose aerogel blocks in addition to chemical vapor deposition method

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