Fabrication And Electrochemical Performance Of Cathode Material For Lithium-sulfur Battery

Compared to the general lithium ion secondary batteries, lithium-sulfur battery with ultra-high specific capacity, low cost, low toxicity and easy recovery and other advantages to the electric car, reserve power and aerospace and other fields with attractive application prospects. Elemental sulfur is a kind of most promising cathode material for the next generation lithium batteries, due to its the highest specific capacity, abundant resources, and low toxicity. However, the insulating nature of sulfur and polysulfides and the loss of polysulfides in the liquid organic electrolyte lead to lithium-sulfur batteries have very low positive active material utilization and poor cyclability. The improved methods are proposed, but lots of material preparation process is more complicated, which is not good for large-scale operation.In this paper we present two simple ways to prepare composites:one is the microwave for expanded graphite-sulfur composites; another one is hydrothermal for graphene-sulfur composites. The composites were characterized by using XRD, SEM, TGA, and elemental analysis systematically. Explore their feasibility as a lithium battery cathode material. And the composite materials prepared above were assembled in to a battery to study.Here we have prepared sulfur-expanded graphite composites by microwave. We studied it from two aspects respectively. First, we studied the effects of different microwave time for material properties at the same proportion. The results show that we could control the sulfur load by change the microwave time. When the time is2min, the sulfur loading is highest and the distribution of sulfur particles is uniform, sulfur particle diameter in the range of100-400nm, and no significant agglomeration. After assembled into battery has the highest discharge capacity650mAhg-1. Second, we studied the effects of different proportion for material properties at the same microwave time. The results show that we could control the sulfur load and the sulfur particles size by control the ratio between sulfur and expanded graphite. When the microwave time is2minutes, the mass ratio is10:1, we could obtain a relatively uniform sulfur particles. Sulfur content and size of the sulfur particles is an important factor for the capacity of a lithium-sulfur battery. When the mass ratio between the sulfur and the expanded graphite is10:1, the assembled battery has the highest discharge capacity1020mAhg-1at0.1C.Here we introduce an one-pot strategy using the hydrothermal reduction of GO and its self-assembly with in situ deposition of sulfur nanocrystals from sulfur compound by chemical reaction, this method is simple and scalable. The graphene-sulfur (G-S). composites can be cut and direct use as Li-S battery electrodes without metal collector, binder and conductive additive. The oxygen-containing functional groups on graphene combined the graphene with the small size of the sulfur ogether strongly reduced the dissolution of polysulfide intermediates into the electrolyte and improved the electrochemical performance. The3D graphene has a complex network structure, abundant pore structures, provides conductive electron transport pathways, can suppress the polysulfide dissolved into the electrolyte. As a result, the ungrounded cathode showed excellent electrochemical performance with high specific capacity (1585mAhg-1), good rate performance and stable cyclability compared with grounded cathode.