Providing More Active Sites via Reactivation of “Dead Li2S” to Enhance the Long Cycle Performance of Lithium–Sulfur Batteries

Accelerating Li2S2/Li2S reduction through catalysis to enhance the apparent conversion kinetics has emerged as an innovative paradigm for a highly efficient lithium–sulfur battery. Nonetheless, the sluggish kinetics of the solid–solid conversion from solid-state intermediate product Li2S2 to the final discharge product Li2S (corresponding to the last 50% of the theoretical capacity) leads to the premature end of discharge and low discharge capacity output and sulfur utilization. Here, we add 1-butyl-1-methylpyrrolidine trifluoromethanesulfonate ([P14][OTf]) to a typical ether electrolyte, which in turn promotes the slow Li2S2/Li2S conversion kinetics by increasing the solubility of Li2S/Li2S2. The three-electrode experimental and characterization studies disclose that the exchange current densities of Li2S2 reduction, Li2S oxidation, and Li2S2 oxidation are up to 2.28 times, 4.6 times, and 1.04 times than those of the control electrolyte, respectively. Furthermore, the modified electrolyte could activate “dead Li2S”, thus providing more reactive sites and inducing small particle Li2S/Li2S2 deposition. Accordingly, the LSBs containing the Control/5 wt % [P14][OTf] electrolyte exhibit a significantly improved capacity rate of 40% compared with the traditional electrolyte at 0.5 C for 500 cycles (corresponding to a fading rate 0.1% per cycle). We believe that increasing Li2S2/Li2S solubility via electrolyte modification provides practical opportunities toward long-life batteries.