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Nowadays, solid electrolytes are considered the main alternative to conventional liquid electrolytes in lithium batteries. The fabrication of these materials is however limited by the strict synthesis conditions, requiring high temperatures which can negatively impact the final performances. Here, it is shown that a modification of garnet-based Li 7 La 3 Zr 2 O 12 (LLZO) and the incorporation of tellurium can accelerate the synthesis process by lowering the formation temperature of cubic LLZO at temperatures below 700 °C. Optimized synthesis at 750 °C showed a decrease in particle size and cell parameter for samples with higher amounts of Te and the evaluation of electrochemical performances reported for LLZO Te0.25 a value of ionic conductivity of 5,15 × 10 À 5 S cm À 1 after hot-pressing at 700 °C, two orders of magnitude higher than commercial Al-LLZO undergoing the same working conditions, and the highest value at this densification temperature. Partial segregation of Te-rich phases occurs for high-temperature densification. Our study shows the advantages of Te insertion on the sintering process of LLZO garnet and demonstrates the achievement of highly conductive LLZO with a low-temperature treatment.

Magnesium-ion batteries represent promising environmentally sustainable energy-storage systems with higher energy densities than their lithium counterparts. In this work, the charge storage mechanisms of the olivine-related compound (Mg0.5Ni0.5)3(PO4)2 using Mg2+ and Li+ ions were investigated and compared for the first time when copper was chosen as the current collector. A comprehensive physicochemical and electrochemical characterization was performed on the pristine powder and electrodes at different states of charge. Although (Mg0.5Ni0.5)3(PO4)2 is electrochemically active, it undergoes irreversible conversion reactions in both Mg and Li chemistries. The conversion reactions proceed with an ionic exchange between structural Ni2+ and Mg2+ or Li+ cations, which results in the formation of sarcopside-Mg3(PO4)2, a Cu–Ni alloy and poorly crystalline Li3PO4, respectively. A capacity of 600 mA h g−1 was achieved with a Li metal counter electrode in the Li cell since the conversion reaction could go to completion. A capacity of 92 mA h g−1 was delivered in the Mg cell using an activated carbon counter electrode. These findings shed light on the fundamental mechanism of activity in olivine-related compounds, underlining the importance of performing systematic studies to unveil the complex interactions between both single-valent and multivalent ions with novel structures.

Magnesium‐ion batteries (MIBs) are a promising alternative to lithium‐ion batteries due to their higher theoretical energy densities and lower cost. However, fundamental limitations such as the sluggish diffusion of Mg2+ ions into cathode materials have hindered their practical implementation. In this work, the structural, morphological and interfacial changes of H2V3O8, a promising cathode material for MIBs, are elucidated upon Mg2+ intercalation in TFSI‐based electrolytes. Post‐mortem analysis revealed a shrinkage of the interlayer distance, an increase in cell volume, and a decrease of the surface V5+/V4+ ratio during discharge. These changes were only partially reversible upon subsequent charge due to Mg trapping. A cathode electrolyte interphase (CEI) formed mainly of TFSI− anions, its decomposition products, and MgF2 was detected on the surface of H2V3O8. The CEI thickness and chemical composition vary upon charge and discharge as well as during prolonged cycling, and its presence correlates with the additional capacity recorded during discharge. Our study aims to contribute to a better understanding of Mg2+ intercalation and cathode‐electrolyte interaction in high voltage cathode materials for MIBs.

The Cover Feature shows the different phenomena occurring when cycling H2V3O8, a promising cathode material for Mg‐ion batteries, in TFSI‐based electrolytes. Post‐mortem analysis showed evidence of Mg trapping into the crystal structure, formation of a cathode electrolyte interphase (CEI) containing TFSI ions and MgF2, and vanadium dissolution into the electrolyte. More information can be found in the Research Article by Y. Surace and co‐workers.