| Lithium-sulfur batteries have a theoretical specific energy as high as 2600 Wh kg-1, far higher than the current commercial lithium-ion batteries. Sulfur used as the positive active material of lithium-sulfur batteries is abundant, cheap and environmentally friendly. So it’s considered as the most promising next generation battery which owns high capacity. However, there are still many problems to be solved: the elemental sulfur and the discharging product lithium sulfide are insulation materials, leading to low utilization of active materials. So it is necessary to add a lot of conductive agent to improve the electrical conductivity of electrode. In the reaction process, the elemental sulfur will produce many intermediate sulfur ions, and sulfur ions can dissolve into the electrolyte to produce shuttle effect. Active substances can produce volume change resulting in destruction of electrode structure in the reaction process. Special structure is prepared in this paper, through the design of conductive polyaniline/silica/sulfur ternary material to improve the electrochemical performance lithium-sulfur batteries. The main research contents and results are as follows:(1) We prepared the sulfur nanoparticles by chemical liquid phase with nano silicon dioxide ultrasonic mixing in deionized water, then used aniline monomer to coated both mateirals to get cellular structure composite material(SPS). The microstructure and phase characterization of SPS composites had been carried on, and it was found that the sulfur nanoparticles was nuclear, coated with conductive polyaniline shell and nano silicon dioxide setting in the shell to obtain the core-shell structure. The size of SPS particle was about 800 nm. SPS materials used into electrode pole piece was used for lithium sulfur batteries. The first discharge specific capacity could reach 805 mAh g-1, and could still keep close to 500 mAh g-1 after the cycle 300 times under the ratio of 0.2 C to charge and discharge, showing the good cycle performance. The unique imitation of the cellular structure was helpful to improve the conductivity of active material and comprehensive utilization of the conductive polyaniline physical barriers and silica shell chemical adsorption.(2) Firstly the nano silicon dioxide was spreadde in aqueous solution, and then by the reaction of sodium thiosulfate and hydrochloric acid, elemental sulfur deposited on the surface of nano silicon dioxide. Through the ammonium persulfate oxidation of aniline monomers, silicon dioxide and sulfur were coated, obtaining a kind of pitaya structure composite SSP. The microstructure and phase characterization of the SSP composite materials was carried on to find a nanometer silicon dioxide as seeds, elemental sulfur for pulp, conductive polyaniline type for the skin of pitaya core-shell structure.The particle size was about 500 nm. The SSP materials used into electrode pole piece was used for lithium sulfur batteries, and it could reach more than 500 mAh g-1 under the ratio of 0.5 C to charge and discharge 230 times, showing the good cycle performance. That was determined by the pitaya structure which was amore optimized structure design. The structure of pitaya in succession based on the advantage of the cellular structure could further improve the electrical conductivity of the composite material, and had spare space to alleviate volume effect of active material, which was advantageous to the cycle performance and rate performance of the battery. |
PDF Full Text Request