Ionic liquid-reinforced carbon nanofiber matrix enabled lean-electrolyte Li-S batteries via electrostatic attraction

Lithium–sulfur (Li–S) batteries are one of the most promising battery technologies to support the fast-expanding electrical vehicle and large-scale energy storage market. Reducing the electrolyte amount is critical for the high specific energy of Li–S batteries in practice. However, using lean electrolytes (that is, with a low Electrolyte to Sulfur (E/S) ratio) always leads to a sluggish sulfur reaction kinetics. Herein, a design strategy based on electrostatic attractions between the cations of ionic liquids and the polysulfide anions is proposed to boost the reaction. The positively charged ionic liquid grafted carbon nanofibers can offer a non-contact coulomb force to attract the polysulfides, accelerate the transport of S species for further strong adsorption and therefore improve the reactant kinetics, especially in a lean electrolyte condition. The electrostatic properties are verified by Zeta potential analysis, Kelvin probe force microscopy test and DFT calculation. As a result, it maintains a high stable discharge capacity of 830 mAh g⁻¹ after 400 cycles (sulfur mass loading: 4.0 mg cm⁻²; electrolyte/sulfur ratio = 5 μl mg⁻¹) and a capacity up to 845 mAh g⁻¹ with an extremely challenging E/S ratio of 3.5 μl mg⁻¹. This work provides a rational guidance for electrostatic design and a new strategy for the development of lean-electrolyte Li-S batteries.