Rechargeable Mg-metal batteries (RMBs) are considered promising alternatives to conventional Li-ion batteries owing to their high volumetric capacity and low cost. In addition, Mg anodes for RMBs do not suffer from metal dendritic growth or internal short circuit. However, the notion that Mg anodes are indeed dendrite-free has recently been under debate, and further clarification is crucial for advancing practical RMBs. In this work, we closely investigated Mg dendrite behaviors under various electrochemical test conditions using operando observation techniques. The critical current density inducing fatal Mg dendritic growth was defined by directly monitoring the dendritic growth process leading to a short circuit. We further propose a new strategy to regulate the dendrite growth by introducing magnesiophilic sites of Au nanoseeds on a substrate. We not only elucidated the effect of the applied current density and capacity utilization on the Mg growth behaviors but also demonstrated the effect of magnesiophilic seeds in suppressing Mg dendrite growth.
Single-atom M-N-C catalysts have attracted tremendous attention for their application to electrocatalysis. Nitrogen-coordinated mononuclear metal moieties (MN x moities) are bio-inspired active sites that are analogous to various metal-porphyrin cofactors. Given that the functions of metal-porphyrin cofactors are highly dependent on the local coordination environments around the mononuclear active site, engineering MN x active sites in heterogeneous M-N-C catalysts would provide an additional degree of freedom for boosting their electrocatalytic activity. This work presents a local coordination structure modification of FeN 4 moieties via morphological engineering of graphene support. Introducing highly wrinkled structure in graphene matrix induces nonplanar distortion of FeN 4 moieties, resulting in the modification of electronic structure of mononuclear Fe. Electrochemical analysis combined with firstprinciples calculations reveal that enhanced electrocatalytic lithium polysulfide conversion, especially the Li 2 S redox step, is attributed to the local structure modified FeN 4 active sites, while increased specific surface area also contributes to improved performance at low C-rates. Owing to the synergistic combination of atomic-level modified FeN 4 active sites and morphological advantage of graphene support, Fe-N-C catalysts with wrinkled graphene morphology show superior lithium-sulfur battery performance at both low and high C-rates (particularly 915.9 mAh g −1 at 5 C) with promising cycling stability.
Hierarchical mesoporous carbon was studied as a key material for enhancing sulfur utilization in Li−S batteries. Commonly, thermal sulfur infiltration into mesoporous carbon was a representative method for S−C composites; however, these had some problems such as pore blocking or nonuniform deposition of sulfur. Electrochemical sulfur impregnation without chemical or thermal infiltration reduced the preprocess time and enabled efficient polysulfide diffusion into the carbon pores. As the soluble polysulfides are smaller and more mobile than solid‐state sulfur, they could be physically or chemically adsorbed into the pores of the carbon additives. This approach enhanced the cycle stability and rate performance of the batteries. This study will provide an efficient and economic use of porous carbons in the Li−S battery field.
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