Imidazolium ionic liquids containing LiBOB electrolyte for lithium battery

Bis(oxlate)borate anion (BOB −) has high reduction potential for 1-ethyl-3-methyl-imdazolium tetrafluoroborate (EMIBF 4) and forms solid electrolyte interface (SEI) on lithium (Li) metal surface. The addition of BOB − may make possible the use of EMIBF 4 for Li metal battery. The electrochemical properties of ionic liquids containing EMIBF 4 were analyzed. We investigated the stability of LiBOB/EMIBF 4 and LiBF 4/EMIBF 4 electrolyte for Li metal and the performance of Li/MnO 2 batteries with the electrolytes by 1H NMR, ac impedance spectra and the electrochemical method. From the 1H NMR spectra, LiBOB/EMIBF 4 was stable for Li metal and LiBF 4/EMIBF 4 was reduced on the surface of Li metal. The discharge capacity of MnO 2 cathode with LiBOB/EMIBF 4 was 235 mAh g −1. Li metal plating and stripping and Li–Al alloying reaction were reversible in LiBOB/EMIBF 4. Charge–discharge reaction of Li–Al alloy in LiBOB/EMIBF 4 had a high coulomb efficiency. The coulomb efficiency at 1st cycle was 86% and the efficiency at 5th cycle was up to 94%.