Conditions Extrêmes et Matériaux : Haute Température et Irradiation
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2021

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Nicolas Dubouis, Thomas Marchandier, Gwenaelle Rousse, Florencia Marchini, François Fauth, Maxim Avdeev, Antonella Iadecola, Benjamin Porcheron, Michael Deschamps, Jean-Marie Tarascon, Alexis Grimaud, 'Extending insertion electrochemistry to soluble layered halides with superconcentrated electrolytes', Nat. Mater. 20 1545–1550 (2021) doi:10.1038/s41563-021-01060-w

Following the discovery of Li-ion batteries, a frenetic race for designing new intercalation compounds started. However, while oxide, sulfide and polyanionic materials exhibit good compatibility with carbonate based electrolytes, other chemistries such as halides were not considered owing to drastic solubility issues. In this work, we demonstrate the possibility to reversibly intercalate lithium into vanadium trihalides (VX3, X = Cl, Br, I) that are widely studied for their physical properties. We followed an electrolyte engineering approach and found that superconcentrated electrolytes can thermodynamically alleviate transition metal dissolution. Doing so, we electrochemically synthetized and characterized using (operando) synchrotron techniques a novel family of LixVX3 phases. Such insights provide a new playground for solid-state chemists to design materials with tunable properties.Insertion compounds provide the fundamental basis of today’s commercialized Li-ion batteries. Throughout history, intense research has focused on the design of stellar electrodes mainly relying on layered oxides or sulfides, and leaving aside the corresponding halides because of solubility issues. This is no longer true. In this work, we show the feasibility of reversibly intercalating Li+ electrochemically into VX3 compounds (X = Cl, Br, I) via the use of superconcentrated electrolytes (5 M LiFSI in dimethyl carbonate), hence opening access to a family of LixVX3 phases. Moreover, through an electrolyte engineering approach, we unambiguously prove that the positive attribute of superconcentrated electrolytes against the solubility of inorganic compounds is rooted in a thermodynamic rather than a kinetic effect. The mechanism and corresponding impact of our findings enrich the fundamental understanding of superconcentrated electrolytes and constitute a crucial step in the design of novel insertion compounds with tunable properties for a wide range of applications including Li-ion batteries and beyond.