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

Accelerating Li 2 S 2 /Li 2 S 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 Li 2 S 2 to the final discharge product Li 2 S (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 Li 2 S 2 /Li 2 S conversion kinetics by increasing the solubility of Li 2 S/Li 2 S 2 . The three-electrode experimental and characterization studies disclose that the exchange current densities of Li 2 S 2 reduction, Li 2 S oxidation, and Li 2 S 2 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 Li 2 S”, thus providing more reactive sites and inducing small particle Li 2 S/Li 2 S 2 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 Li 2 S 2 /Li 2 S solubility via electrolyte modification provides practical opportunities toward long-life batteries.