Benzimidazole-derived anion for lithium-conducting electrolytes

• New salt for lithium conducting electrolytes, the LiTDBI, is presented.
• Salt has been synthesized, characterized spectroscopically and electrochemically.
• Salt is stable up to 270 °C and up to 4.7 V vs Li.
• Electrolytes have conductivity >1 mS cm−1 and very high Li+ transference number, 0.75.
• Salt has been tested in half-cell with graphite, showing good capacity retention.

In this work we announce new lithium salt of 5,6-dicyano-2-(trifluoromethyl)benzimidazolide (LiTDBI) designed for application in lithium conductive electrolytes. It was synthesized and completely characterized by NMR techniques. Studies show salt's thermal stability up to 270 °C and electrochemical stability in liquid solvents up to +4.7 V vs. metallic lithium anode. Basic characterization of electrolytes made with this salt show conductivity over 1 mS cm−1 and unusually high transference number at high concentrations (0.74 in EC:DMC 1:2 ratio mixture) along with low onset of conductivity peak. As a final proof of concept, cycling in half-cell was performed and electrolyte based on LiTDBI showed perfect capacity retention. Such properties show remarkable progress in creating efficient lithium-conducting electrolytes with use of weakly-coordinating anions.