A top-down approach to build Li2S@rGO cathode composites for high-loading lithium–sulfur batteries in carbonate-based electrolyte

Li2S In Situ Grown on Three-Dimensional Porous Carbon Architecture with Electron/Ion Channels and Dual Active Sites as Cathodes of Li-S Batteries

Li₂S-based Li-S batteries are taken as promising energy storage systems due to the high theoretical specific capacity/energy density and nature of a matching Li-metal-free anode. However, the cyclic stability of the Li₂S-based Li-S battery is seriously prevented by the shuttle effect of lithium polysulfides (LiPSs). Meanwhile, due to the poor electrical conductivity of Li₂S, the Li-S battery displays slow reaction kinetics. In this work, we design 3D-porous carbon (PC) architecture as a host for inhabiting the LiPS shuttle based on physical capture. Furthermore, this porous carbon architecture is modified by introducing two kinds of heteroatoms (N and S) to form dual active sites (named as NSPC) for chemically binding LiPSs and accelerating their conversion. The polyvinyl pyrrolidone-coated Li₂SO₄·H₂O is embedded in the NSPC skeleton and further forms the Li₂S/NSPC cathode via a carbothermal reduction process. In consequence, the NSPC architecture possesses continuous electron/ion channels and abundant active sites, which are beneficial to the fast diffusion of Li⁺ and timely conversion of sulfur species. As a result, the as-prepared Li₂S/NSPC cathode exhibits a high initial discharge capacity of 690 mAh g^-1 at a high rate of 1C and keeps a capacity of 587 mAh g^-1 after 200 cycles with a good capacity retention rate of 85% and low fading rate of 0.075% per cycle. Therefore, this work offers a brand-new platform to understand the synergistic effects of promoting reaction kinetics for Li₂S-based Li-S batteries.

Defect Control in the Synthesis of 2 D MoS2 Nanosheets: Polysulfide Trapping in Composite Sulfur Cathodes for Li-S Batteries

One of the inherent challenges with Li-S batteries is polysulfide dissolution, in which soluble polysulfide species can contribute to the active material loss from the cathode and undergo shuttling reactions inhibiting the ability to effectively charge the battery. Prior theoretical studies have proposed the possible benefit of defective 2 D MoS₂ materials as polysulfide trapping agents. Herein the synthesis and thorough characterization of hydrothermally prepared MoS₂ nanosheets that vary in layer number, morphology, lateral size, and defect content are reported. The materials were incorporated into composite sulfur-based cathodes and studied in Li-S batteries with environmentally benign ether-based electrolytes. Through directed synthesis of the MoS₂ additive, the relationship between synthetically induced defects in 2 D MoS₂ materials and resultant electrochemistry was elucidated and described.

A new high-capacity and safe energy storage system: lithium-ion sulfur batteries

Lithium-ion sulfur batteries as a new energy storage system with high capacity and enhanced safety have been emphasized, and their development has been summarized in this review. The lithium-ion sulfur battery applies elemental sulfur or lithium sulfide as the cathode and lithium-metal-free materials as the anode, which can be divided into two main types. One is anode-type, where elemental sulfur is applied as the cathode, and the anode provides lithium ions. The other one is cathode-type, where lithium sulfide as the cathode provides lithium ions, and lithium-metal-free materials (e.g., graphite, silicon/carbon) function as the anode. Recently, some new lithium-ion sulfur battery systems have also been proposed, and are discussed in this review as well. The lithium-ion sulfur batteries not only maintain the advantage of high energy density because of the high capacities of sulfur and lithium sulfide, but also exhibit the improved safety of the batteries due to a non-lithium-metal in the anode. This review paper aims to track the recent progress in the development of lithium-ion sulfur batteries and summarize the challenges and the approaches for improving their electrochemical performances, including the lithiation methods to prepare lithium-metal-free anodes in anode-type lithium-ion sulfur batteries and the lithium sulfide cathode modification approaches in cathode-type lithium-ion sulfur batteries. Furthermore, the challenges and perspectives for future research and commercial applications have also been enumerated.