Electrochemical and Physical Properties of Imidazolium Chloride Ionic Liquids with Pyrrolidinium or Piperidinium Cation Addition and Their Application in Dual‐Ion Batteries

Herein, nonflammable ionic liquid (IL) electrolytes are prepared for dual‐ion batteries (DIBs) by mixing 1‐methyl‐1‐propylpyrrolidinium chloride (P 13 Cl) or 1‐butyl‐1‐methylpiperidinium chloride (PP 14 Cl) with 1,2‐dimethyl‐3‐propylimidazolium chloride (DMPICl)/aluminum chloride (AlCl 3 ) to form mixed IL electrolytes. Then, viscosity, ionic conductivity, thermal stability, and electrochemical limits measurements are recorded to reveal the fundamental properties of the mixed IL electrolytes for DIBs, which are not reported previously. As compared with DMPICl/AlCl 3 (=1 in mole ratio) electrolyte, using electrolyte with addition of P 13 Cl or PP 14 Cl (e.g., 0.63 mole to replace DMPICl), the DIB with graphite electrodes show better electrochemical stability. With the addition of 0.63 P 13 Cl, the Coulombic efficiency of the DIB reaches up to 96.7% (≈91% for DMPICl/AlCl 3 ); however, specific capacity loss should be considered. In general, ideas for designing higher energy density electrochemical energy storage devices are provided.