Experimental and computational studies of electrochemical anion intercalation into graphite from target-oriented designed borate-based ionic liquid electrolytes

Here, we report on the fundamental experimental and computational analyses of target-oriented designed ionic liquid (IL) electrolytes composed of small and (electro)chemically stable borate-based anions with respect to their anion intercalation/de-intercalation behavior in graphite positive electrodes for dual-ion batteries (DIBs). Due to their relatively small size, borate-based anions (e.g., BF4ˉ) and electrolytes are of high interest for DIB cells in order to achieve a high specific capacity, which can, however, be impeded by electrolyte solvation effects. In order to exclude solvent effects, we develop and synthesize novel room-temperature IL electrolytes (RTILs), i.e., Pyr1101BF4/LiBF4 and Pyr1101CF3BF3/LiCF3BF3, which are characterized with respect to stability and anion intercalation behavior. These studies are combined with computational studies to gain fundamental insights into the electronic structures of the BF4ˉ and CF3BF3ˉ acceptor-type graphite intercalation compounds (GICs), staging stoichiometries, theoretical capacities and anion transport properties. [Display omitted] •Experimental and computational studies of anion intercalation into graphite.•Target-oriented design of borate-based ionic liquid electrolytes.•Synthesis of novel Pyr1101BF4/LiBF4 and Pyr1101CF3BF3/LiCF3BF3 electrolytes.•Insights into electronic structures of graphite intercalation compounds.•Analysis of transport properties of BF4ˉ and CF3BF3ˉ anions within graphite.