Preparation Of Mesoporous Carbon/Sulfur Composite Loaded With ZnS And Its Property For Lithium-Sulfur Batteries

To obtain high performance cathode materials for Li-S batteries, mesoporous carbon/sulfur composite loaded with ZnS was prepared and its performance was studied. At the same time, the effect of different electrolyte additives on the performance of Li-S batteries were discussed. The main contents and results are as follows:1. Mesoporous carbon was synthesized by a hard template method with sucrose as the carbon source and SBA -15 as template. With mesoporous carbon as the carrier and zinc nitrate as the source of zinc, sodium sulfide as sulfur source, composites of mesoporous carbon (MC) loaded with ZnS (ZnS/MC) were prepared by combining the liquid phase deposition and refluxing-heating treatment method. The materials were characterized by X-ray powder diffraction(XRD), EDS, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and N2 adsorption-desorption isotherms. The results showed that composites of mesoporous carbon (MC) loaded with ZnS (ZnS/MC) were obtained by the approach mentioned above. The specific surface area, average pore diameter and pore volume of the composite materials reduced; the structure characteristics of ZnS/MC were similar to mesoporous carbon, it was closed to amorphous substance and remained a highly porous structure. When the content of ZnS was less than 17%, there was no independent ZnS crystal formed in composites; when that was larger than 17%, sphalerite ZnS crystal phase was formed and distributed uniformly over the surface of the mesoporous carbon and mesoporous carbon channel in the form of nanoparticles, also, some distributed in carbon clearance. When ZnS content was larger than 50%, ZnS nanoparticles would aggregate together by heating. The mesoporous carbon/sulfur composite loaded with ZnS were obtained from ZnS/MC and elemental sulfur following a melt-diffusion strategy. In this paper, cyclic voltammetry, the electrochemical performance of composite cathode and the affect of different content of ZnS on the performance of lithium sulfur batteries were characterized by ac impedance, constant current charge-discharge, and so on. The research results proved that ZnS nanoparticles existed in composite performed high reaction activity, it could catalyze the oxidation of polysulfide. Composite electrode had the best performance when the content of ZnS was 50%, the initial discharge specific capacity was 1354.6 mA h/g, the initial reversible capacity was 1251.4 mA h/g, the coulomb efficiency of capacity in the first charge and discharge was 98.7%, and that of each cycle was close to 100%. After 50 cycles, the capacity still remained 650.0 mA h/g.2. The influence of electrolyte additives(LiNO3, SOCl2) on the performance of lithium sulfur batteries were explored. Charge-discharge tests showed that the initial discharge specific capacity of sulfur electrode was 1183.2 mA h/g when LiNO3 was used as additive; its capacity remained 696.4 mA h/g after 50 cycles. With SOCl2 as additive, the initial irreversible capacity was up to 1252 mA h/g, and the coulomb efficiency was close to 100% during all cycles. After 60 cycles, its capacity still maintained 641.8 mA h/g. For the use of LiNO3 and SOCl2 in the electrolyte, the performance of sulfur electrode was improved because the"shuttle effect" was effectively restrained.3. The impact of soluble polysulfide on the performance of lithium sulfur batteries were also investigated. Researches certified that the discharge capacity and cycle stability were improved by using the electrolyte with polysulfide dissolved. The initial reversible capacity was 1227 mA h/g, the coulomb efficiency was close to 100%. After 50 cycles, the capacity still remained 664.5 mA h/g.