Boronium-cation-based room-temperature ionic liquids (RTILs) were applied for the first time as novel supporting electrolytes in rechargeable LiLiFePO4 batteries. The physicochemical properties of three different materials (L~1L~2)BH2-NTf2, 3a (L~1, L~2 = 1-methyl imidazole (mim)), 3b (L~1, L~2 = 1-bulylimidazole (bim), and 3c (L~1 = trimethylamine (N_(111)), L~2 = dimethylethylamine (N_(112))), which are readily synthesized from inexpensive and commercially available starting materials, were established by DSC. TGA, conductivity, and cyclic voltammetry. These RTILs are stable up to between 238 and 335 °C and display sufficient conductivities and electrochemical windows (4.3-5.8 V) to be compatible with the Li anode of a battery. Stable battery cycling with good capacity retention was possible for > 300 cycles with (N_(111))(N_(112))BH2-NTf2 + LiNTf2 solutions at charge -discharge rates C/10 and C/5 between 50 and 30 °C. By contrast, a C4mpyr-NTf2 + LiNTf2 electrolyte system performed less well under the same conditions despite the higher conductivity of C4mpyr-NTf2 compared to the boronium RTIL 3c. Li battery cycling was also possible with the imidazole units containing material (bim)2BH2-NTf2 for 140 cycles at 80 °C. These new materials could emerge as important electrolytes for various electrochemical applications.
展开▼
