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Magnesium (Mg) anode-electrolyte interaction is not trivial and investigation of the interfacial process can be helpful for the development of Mg batteries. In this work, we studied the Mg metal anode cycled in a chloride (Cl)-free magnesium tetrakis (hexafluoroisopropyloxy) borate electrolyte using a full-cell configuration with TiS$_{2}$ model cathode. Electrochemical measurements and structural analysis of the cathode showed reversible de-/magnesiation of TiS$_{2}$ with some entrapment of irreversibly bound Mg$^{2+}$. Electrochemical impedance spectroscopy (EIS) was applied to analyze the Mg-electrolyte interaction in a three-electrode system. The results showed a rapid increase in charge transfer resistance on the anode side with increasing resting time. In contrast, we observed a significant drop in the charge transfer impedance upon cycling along with the appearance of an additional semi-circle, which suggested to the development of a solid interphase. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) corroborated the EIS results and confirmed the solid interphase layer formation, in which MgF$_{2}$ was identified as the primary species contributing to its formation. The current study provides fundamental insights into the interfacial phenomena between the metallic Mg anode and Cl-free electrolyte by highlighting the role played by the formed interphase on the reversible Mg stripping and plating in a Mg full-cell.

Making the difference: The influence of different additives on the oxygen reduction reaction/oxygen evolution reaction (ORR/OER) behavior in a Mg���containing ionic liquid N���butyl���N���methylpyrrolidinium bis(trifluoromethanesulfonyl)imide on glassy carbon was studied by differential electrochemical mass spectrometry. The addition of a stoichiometric excess of additives reduced the tendency to passivate the electrode surface but also the reversibility of the ORR/OER. The influence of different additives on the oxygen reduction reaction/oxygen evolution reaction (ORR/OER) in magnesium���containing N���butyl���N���methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([BMP][TFSI]) on a glassy carbon electrode was investigated to gain a better understanding of the electrochemical processes in Mg���air batteries. 18���Crown���6 was used as a complexing agent for Mg ions to hinder the passivation caused by their reaction with ORR products such as superoxide and peroxide anions. Furthermore, borane dimethylamine complex (NBH) was used as a potential water���removing agent to inhibit electrode passivation by reacting with trace impurities of water. The electrochemical processes were characterized by differential electrochemical mass spectrometry to monitor the consumed and evolved O2 in the ORR/OER and determine the number of transferred electrons. Crown ether and NBH efficiently masked Mg2+. A stochiometric excess of crown ether resulted in reduced formation of a passivation layer, whereas at too high concentrations the reversibility of the ORR/OER was diminished., publishedVersion

Lithium‐rich layered oxides (LRLOs) exhibit specific capacities above 250 mAh g$^{-1}$, i.e., higher than any of the commercially employed lithium‐ion‐positive electrode materials. Such high capacities result in high specific energies, meeting the tough requirements for electric vehicle applications. However, LRLOs generally suffer from severe capacity and voltage fading, originating from undesired structural transformations during cycling. Herein, the eco‐friendly, cobalt‐free Li$_{1.2}$Ni$_{0.2}$Mn$_{0.6}$O$_{2}$ (LRNM), offering a specific energy above 800 Wh kg$^{-1}$ at 0.1 C, is investigated in combination with a lithium metal anode and a room temperature ionic liquid‐based electrolyte, i.e., lithium bis(trifluoromethanesulfonyl)imide and N‐butyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide. As evidenced by electrochemical performance and high‐resolution transmission electron microscopy, X‐ray photoelectron spectroscopy, and online differential electrochemical mass spectrometry characterization, this electrolyte is capable of suppressing the structural transformation of the positive electrode material, resulting in enhanced cycling stability compared to conventional carbonate‐based electrolytes. Practically, the capacity and voltage fading are significantly limited to only 19% and 3% (i.e., lower than 0.2 mV per cycle), respectively, after 500 cycles. Finally, the beneficial effect of the ionic liquid‐based electrolyte is validated in lithium‐ion cells employing LRNM and Li$_{4}$Ti$_{5}$O$_{12}$. These cells achieve a promising capacity retention of 80% after 500 cycles at 1 C.

Li-rich disordered rock-salt oxides such as Li$_{1.2}$Ni$_{1/3}$Ti$_{1/3}$Mo$_{2/15}$O$_{2}$ are receiving increasing attention as high-capacity cathodes due to their potential as high-energy materials with variable elemental composition. However, the first-cycle oxygen release lowers the cycling performance due to cation densification and structural reconstruction on the surface region. This work explores the influence of lithium excess on the charge compensation mechanism and the effect of surface modification with LiNbO$_{3}$ on the cycling performance. Moving from a stoichiometric LiNi$_{0.5}$Ti$_{0.5}$O$_{2}$ composition toward Li-rich Li$_{1.2}$Ni$_{1/3}$Ti$_{1/3}$Mo$_{2/15}$O$_{2}$, oxygen redox is accompanied by oxygen release. Thereby, cationic charge compensation is governed by the Ni$^{2+/3+}$ and Mo$^{3+/6+}$ redox reaction. Contrary to the bulk oxidation state of Mo$^{6+}$ in the charged state, a mixed Mo valence on the surface is found by XPS. Furthermore, it is observed that smaller particle sizes result in higher specific capacities. Tailoring the surface properties of Li$_{1.2}$Ni$_{1.3}$Ti$_{1/3}$Mo$_{2/15}$O$_{2}$ with a solid electrolyte layer of LiNbO$_{3}$ altered the voltage profile, resulting in a higher average discharge voltage as compared to the unmodified material. The results hint at the interdiffusion of cations from the metal oxide surface coating into the electrode material, leading to bulk composition changes (doping) and a segregated Nb-rich surface. The main finding of this work is the enhanced cycling stability and lower impedance of the surface-modified compound. We argue that surface densification is mitigated by the Nb doping/surface modification.