Graphene quantum dots as sulfiphilic and lithiophilic mediator toward high stability and durable life lithium-sulfur batteries

The development of lithium-sulfur (Li-S) battery as one of the most attractive energy storage systems among lithium metal batteries is seriously hindered by low sulfur utilization, poor cycle stability and uneven redeposition of Li anode. It is necessary to propose strategies to address the problems as well as improve the electrochemical performance. One of the effective solutions is to improve the sulfiphilicity of sulfur cathode and the lithiophilicity of the Li anode. Herein, we reported that a synergistic functional separator (graphene quantum dots (GQDs)-polyacrylonitrile (PAN) @polypropylene (PP) separator) improved the electrochemical activity of sulfur cathode as well as the stability of Li anode. GQDs induced uniform Li+ nucleation and deposition, which slowed down the passivation of Li anode and avoided short-circuit. Further, three-dimensional network constructed by electrospinning nanofibers and the polar functional groups of GQDs could both effectively inhibit the shuttle of LiPSs and improve the sulfur utilization. The stability of Li-S battery was improved by the synergistic effect. In addition, GQDs and electrospinning nanofibers protector increased lifetime of separators. Benefiting from the unique design strategy, Li//Li symmetric battery with GQDs-PAN@PP separators exhibited stably cycling for over 600 h. More importantly, the Li-S full batteries based GQDs-PAN@PP separators enabled high stability and desirable sulfur electrochemistry, including high reversibility of 558.09 mA h g−1 for 200 cycles and durable life with a low fading rate of 0.075% per cycle after 500 cycles at 0.5 C. Moreover, an impressive areal capacity of 3.23 mA h cm−2 was maintained under high sulfur loading of 5.10 mg cm−2. This work provides a new insight for modification separator to improve the electrochemical performance of Li-S/Li metal batteries.