Manthiram and colleagues have validated a Li + -ion mediation approach to enhance the electrochemical reversibility of ambient-temperature aluminumsulfur (Al-S) battery chemistry. They systematically investigated the relevant mechanisms with combined experimental and theoretical methodologies. Al-S chemistry is attractive for the development of high-energy, low-cost, safe, nextgeneration electrochemical energy storage technologies.

attract increasing attention. [2] However, the progress in Ca 2+ -ion batteries is very sluggish due to multiple difficulties. One major challenge is the lack of applicable electrolytes that can provide a proper function for the stripping and plating of calcium metal. [3] Another challenge is the difficulty in realizing proper cathode host materials. As a matter of fact, there are substantial differences in the interaction behavior between the divalent Ca 2+ -ion and that of the monovalent Li + -ion. [4] Therefore, neither theoretical guidance nor practical experience with Li + -ion intercalation cathode materials may be straightforwardly adopted for the development of Ca 2+ -ion batteries.In an early stage, V 2 O 5 has been explored as an intercalation-type cathode for Ca 2+ -ion batteries, but the utilization of Ca is very low. [5] Ca-SOCl 2 battery systems have also been exploited, but the utilization of the SOCl 2 electrode is very low due to the passivation of the electrode. [6] In recent years, an intercalation cathode CaCo 2 O 4[7] and various conversion-type hexacyanoferratebased cathodes [8] have been investigated. The Ca 2+ -ion cells demonstrated with these cathode materials have shown interesting performances. However, the capacity of these materials is intrinsically low. Nonaqueous metal-sulfur batteries based on a sulfur cathode chemistry have recently been considered as a promising solution for the development of nextgeneration electrochemical energy storage technologies. [9] Sulfur can facilitate a 2-electron charge transfer and theoretically deliver a high gravimetric capacity of 1672 mA h g −1 . In addition to the primary emphasis on lithium-sulfur (Li-S) batteries, [10] sodiumsulfur batteries, [11] magnesium-sulfur (Mg-S) batteries, [12] potassium-sulfur batteries, [13] and aluminum-sulfur (Al-S) batteries [14] have also received significant attention. However, to date, there has been only one study on calcium-sulfur (Ca-S) batteries, and the Ca-S cells demonstrated in that study were not reversible. [15] Furthermore, the Ca-S cell showed a low discharge voltage due to lack of an effective electrolyte.Herein, we present, for the first time, a reversible Ca-S battery enabled by a lithium-ion mediation strategy. The Ca-S battery is developed with a hybrid electrolyte comprised of a mixture of lithium and calcium ions. In addition to enabling the reversibility of Ca-S chemistry, the use of Li + -ion mediated electrolyte enhances the ionic charge transfer, thus both utilization of the active sulfur cathode and the discharge voltage of the Ca-S batteries are significantly improved.Calcium represents a promising anode for the development of high-energydensity, low-cost batteries. However, a lack of suitable electrolytes has restricted the development of rechargeable batteries with a Ca anode. Furthermore, to achieve a high energy density system, sulfur would be an ideal cathode to couple with the Ca anode. Unfortunately, a reversible calciumsulfur (Ca-S) battery has not yet been reported. Herein,...

Electrolyte and electrode materials used in lithium-ion batteries have been studied separately to a great extent, however the structural and dynamical properties of the electrolyte-electrode interface still remain largely unexplored despite its critical role in governing battery performance. Using molecular dynamics simulations, we examine the structural reorganization of solvent molecules (cyclic ethylene carbonate : linear dimethyl carbonate 1 : 1 molar ratio doped with 1 M LiPF) in the vicinity of graphite electrodes with varying surface charge densities (σ). The interfacial structure is found to be sensitive to the molecular geometry and polarity of each solvent molecule as well as the surface structure and charge distribution of the negative electrode. We also evaluated the potential difference across the electrolyte-electrode interface, which exhibits a nearly linear variation with respect to σ up until the onset of Li ion accumulation onto the graphite edges from the electrolyte. In addition, well-tempered metadynamics simulations are employed to predict the free-energy barriers to Li ion transport through the relatively dense interfacial layer, along with analysis of the Li solvation sheath structure. Quantitative analysis of the molecular arrangements at the electrolyte-electrode interface will help better understand and describe electrolyte decomposition, especially in the early stages of solid-electrolyte-interphase (SEI) formation. Moreover, the computational framework presented in this work offers a means to explore the effects of solvent composition, electrode surface modification, and operating temperature on the interfacial structure and properties, which may further assist in efforts to engineer the electrolyte-electrode interface leading to a SEI layer that optimizes battery performance.

No abstract