Insertion compounds provide the fundamental
basis of today’s commercialized Li-ion batteries. Throughout history, intense
research has focus 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 for the
first time the feasibility to reversibly intercalate electrochemically Li<sup>+</sup>
into VX<sub>3</sub> compounds (X = Cl, Br, I) via the use of superconcentrated
electrolytes, (5 M LiFSI in dimethyl carbonate), hence opening access to a
novel family of Li<sub>x</sub>VX<sub>3</sub> phases. Moreover, through an
electrolyte engineering approach we unambiguously prove that the positive attribute
of superconcentrated electrolytes against 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 beyond Li-ion batteries.
Superconcentrated Electrolytes Widens Insertion Electrochemistry to Soluble Layered Halides