Drastic Effect of Salt Concentration in Ionic Liquid on Performance of Lithium Sulfur Battery

Lithium sulfur (Li–S) battery is an appealing energy storage system due to its high theoretical specific capacity and specific energy. However, two main challenges, lithium polysulfides (LPS) dissolution from the sulfur cathode and the unstable Li anode, impede the practical application of Li–S battery. Developing advanced electrolyte is an effective strategy to tune the stability of both sulfur cathode and Li anode. Here, a concentrated imidazolium-based ionic liquids (IL) electrolyte was explored for Li–S battery with the synergistic advantages of both IL and high concentrated electrolyte. A systematic study was conducted to reveal the effect of salt concentration on the properties of the IL electrolyte and the electrochemical performances of Li–S battery. It is found that an effective suppression of LPS dissolution and improved stability of Li anode can be obtained with increase of salt concentration. As a result, a good cycling stability of the Li–S battery is achieved in the concentrated IL electrolyte, with high capacity retention of 92% after 100 cycles at current density of 0.1 C. The concentrated electrolyte based on IL solvent exhibits good compatibility with both cathode and anode, offering a new opportunity for designing electrolyte to achieve stable electrochemical system.