Mixing ionic liquids and ethylene carbonate as safe electrolytes for lithium-ion batteries

With aim to design safety and high electrochemical-stability electrolytes, mixtures ionic liquids (ILs) – ethylene carbonate have been prepared and investigated for lithium-ion cell using LiMn₂O₄ (LMO) and LiFePO₄ (LFP) as cathode materials. The addition of 20 vol% ethylene carbonate (EC) could decrease significantly the viscosity as well as improve ionic conductivity and cycling performance of the electrolyte at room temperature. In the electrolyte containing 20 vol% EC, lithium-ion diffusion coefficient is still lower than commercial one based on conventional solvents. However, the stable charge - discharge behavior with N,N‑dimethyl‑N‑ethyl‑N‑propylammonium bis(trifluoromethanesulfonyl) imide (N₁₁₂₃TFSI) based mixtures was achieved up to 120 mAh·g⁻¹ in the first cycle and remaining round 100 mAh·g⁻¹ within 20 cycles without any noticeable capacity loss, and a little bit lower with respect to 1‑ethyl‑3‑methylimidazolium bis(trifluoromethanesulfonul)imide (EMITFSI) and N,N‑dimethyl‑N‑ethyl‑N‑butylammonium bis(trifluoromethanesulfonyl) imide (N₁₁₂₄TFSI). The results also showed that the solvent addition up to 25 vol% maintained homogenous solution and good electrochemical stability of the electrolytes.