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Rechargeable aqueous zinc–metal batteries (AZBs) are a promising complimentary technology to the existing lithium‐ion batteries and the re‐emerging lithium–metal batteries to satisfy the increasing demands on energy storage. Despite considerable progress achieved in the past years, the fundamental understanding of the solid‐electrolyte interphase (SEI) formation and how its composition influences the SEI properties are limited. This review highlights the functionalities of anion‐tuned SEI on the reversibility of zinc–metal anode, with a specific emphasis on new structural insights obtained through advanced characterizations and computational techniques. Recent efforts in terms of key variables that govern the interfacial behaviors to improve the long‐term stability of zinc anode, i.e., Coulombic efficiency, plating morphology, dendrite formation, and side‐reactions, are comprehensively reviewed. Lastly, the remaining challenges and future perspectives are presented, providing insights into the rational design of practical high‐performance AZBs. [ABSTRACT FROM AUTHOR]

FSI−‐based ionic liquids (ILs) are promising electrolyte candidates for long‐life and safe lithium metal batteries (LMBs). However, their practical application is hindered by sluggish Li+ transport at room temperature. Herein, it is shown that additions of bis(2,2,2‐trifluoroethyl) ether (BTFE) to LiFSI‐Pyr14FSI ILs can effectively mitigate this shortcoming, while maintaining ILs′ high compatibility with lithium metal. Raman spectroscopy and small‐angle X‐ray scattering indicate that the promoted Li+ transport in the optimized electrolyte, [LiFSI]3[Pyr14FSI]4[BTFE]4 (Li3Py4BT4), originates from the reduced solution viscosity and increased formation of Li+‐FSI− complexes, which are associated with the low viscosity and non‐coordinating character of BTFE. As a result, Li/LiFePO4 (LFP) cells using Li3Py4BT4 electrolyte reach 150 mAh g−1 at 1 C rate (1 mA cm−2) and a capacity retention of 94.6% after 400 cycles, revealing better characteristics with respect to the cells employing the LiFSI‐Pyr14FSI (operate only a few cycles) and commercial carbonate (80% retention after only 218 cycles) electrolytes. A wide operating temperature (from −10 to 40 °C) of the Li/Li3Py4BT4/LFP cells and a good compatibility of Li3Py4BT4 with LiNi0.5Mn0.3Co0.2O2 (NMC532) are demonstrated also. The insight into the enhanced Li+ transport and solid electrolyte interphase characteristics suggests valuable information to develop IL‐based electrolytes for LMBs. [ABSTRACT FROM AUTHOR]

Iron sulfides are promising materials for lithium‐ and sodium‐ion batteries owing to their high theoretical capacity and widespread abundance. Herein, the performance of an iron sulfide‐carbon composite, synthesized from a Fe‐based metal–organic framework (Fe‐MIL‐88NH2) is reported. The material is composed of ultrafine Fe7S8 nanoparticles (<10 nm in diameter) embedded in a heteroatom (N, S, and O)‐doped carbonaceous framework (Fe7S8@HD‐C), and is obtained via a simple and efficient one‐step sulfidation process. The Fe7S8@HD‐C composite, investigated in diethylene glycol dimethyl ether‐based electrolytes as anode material for lithium and sodium batteries, shows high reversible capacities (930 mAh g−1 for lithium and 675 mAh g−1 for sodium at 0.1 A g−1). In situ X‐ray diffraction reveals an insertion reaction to occur in the first lithiation and sodiation steps, followed by conversion reactions. The composite electrodes show rather promising long‐term cycling stability and rate capability for sodium storage in glyme electrolyte, while an improved rate capacity and long‐term cycling stability (800 mAh g−1 after 300 cycles at 1 A g−1) for lithium can be achieved using conventional carbonates. [ABSTRACT FROM AUTHOR]

The electroactivity of sodium‐rich manganese hexacyanoferrate (MnHCF) material constituted of only abundant elements, as insertion host for Li‐ and Na‐ions is herein comprehensively discussed. This material features high specific capacities (>130 mAh g−1) at high potentials when compared to other materials of the same class, i.e., Prussian blue analogs. The reversible electronic and structural modifications occurring during ion release/uptake, which are responsible for such high specific capacity, are revealed herein. The in‐depth electronic and structural analysis carried out combining X‐ray diffraction and X‐ray absorption spectroscopy (XAS), demonstrates that both Fe and Mn sites are involved in the electrochemical process, being the high delivered capacity the result of a reversible evolution in oxidation states of the metallic centers (Fe3+/Fe2+ and Mn2+/Mn3+). Along with the Mn2+/Mn3+ oxidation, the Mn local environment experiences a substantial yet reversible Jahn–Teller effect, being the equatorial Mn‐N distances shrunk by 10% (2.18 Å → 1.96 Å). Na‐rich MnHCF material offers slightly higher performance upon uptake and release of Na‐ions (469 Wh kg−1) than Li‐ions (457 Wh kg−1), being, however, the electronic and structural transformation independent of the adopted medium, as observed by XAS spectroscopy. [ABSTRACT FROM AUTHOR]

Electrolytes based on organic carbonates are widely used for sodium‐ion batteries (SIBs) due to several advantages such as high ionic conductivity, wide liquidus range, and high electrochemical stability. In this work, this class of electrolyte is investigated focusing on two conductive salts, namely NaPF6 (sodium hexafluorophosphate) and NaTFSI (sodium bis(trifluoromethanesulfonyl)imide), using PC (propylene carbonate) as solvent. The investigation of different salt concentrations, from rather diluted to highly concentrated (i.e., 0.1, 1, and 3 m), extends from their glass transition temperature to viscosity, ionic conductivity, electrochemical stability window, and electrochemical stability toward Al. Raman spectroscopy discloses the salt–solvent coordination and its possible modification due to changes in temperature, proving that the viscosity played a major role in influencing ionic conductivity rather than ions and molecules' coordination. Finally, the electrochemical performance of half‐cells employing NaxNi0.22Co0.11Mn0.66O2 as the cathode material with the various electrolytes is also reported, and cells containing electrolyte with 1 m salt concentration outperform the other in terms of delivered capacity and rate performance. The ionic conductivity of high‐concentration sample strongly decreases with decreasing temperatures, differently than samples with lower concentrations. This is an effect of the dramatic change of viscosity by cooling down the samples, rather than related to the different coordination of electrolyte's molecules. [ABSTRACT FROM AUTHOR]

Silicon‐based compounds are interesting candidate anode materials but show only relatively low electrochemical performances with sodium. Controversial reports are available about the electrochemical interaction between Na and silicon, which encourage to investigate the mechanism in a silicon‐based material in detail. This study reports the results of a systematic investigation of the electrochemical sodium ion storage in silicon oxycarbide (SiCO) using ex situ X‐ray photoelectron spectroscopy and magic‐angle spinning nuclear magnetic resonance spectroscopy. Comparison of pristine and hydrofluoric acid‐etched silicon oxycarbide shows that the silicon oxycarbide is active itself, but not by an alloying process. Instead, results reveal an irreversible structural change and amorphization of SiCO upon the initial sodium uptake and support the existence of reversible insertion‐based reactions in the subsequent cycles. A systematic investigation of the electrochemical sodium ion storage in silicon oxycarbide (SiCO) is reported. In this mechanistic study, reversible redox activity of Si during an insertion process is proved; furthermore, the existence of an alloying reaction between sodium and silicon or a reversible conversion reaction to form silicon carbide (SiC) is excluded. [ABSTRACT FROM AUTHOR]