Research On Cathode Materials And Separators For Lithium-sulfur Batteries

Lithium/sulfur battery, fabricated with metal lithium as anode and sulfur as cathode, due to its high theoretical energy density 2600 Wh/kg, while the theoretical capacity of sulfur is 1 680 mAh/g, far more than 5 times more than lithium batteries, lower than lithium-air battery, has become the hot research of electric vehicles and power plant energy storage battery. However, there are some problems of sulfur cathode, due to the strong chemical activity of metallic lithium, insulating properties of sulfur and a mass discharge product of lithium polysulfide dissolved in liquid electrolyte, the dissolution of polysulfides caused diffusion between lithium electrode and sulfur electrode formed Shuttle phenomenon, which lead to low cycling efficiency, short cycle life, and a high self-discharge rate of lithium-sulfur battery, lithium sulfur batteries are difficult to commercialize. Focusing on the problem, we researched the sulfur composite materials of the secondary lithium sulfur battery, also include films materials, the main contents of this thesis are as follows:(1) The sulfur-BP2000 of better performance composites material with using the grinding and heating method. These sulfur, sulfur-acetylene black and sulfur-BP2000 composites cathode materials its crystal structure, morphology and electrochemical properties were characterized. Through the XRD analysis revealed that sulfur and sulfur-black pearls the prepared sample physical combination, didn't have chemical reaction, BET and SEM suggested that grind and thermal method can be more evenly to sulfur particles dispersed as micropores of BP2000. The electrochemical reaction indicated which the larger initial discharge specific capacity of 980 mAh/g at 0.1C, as the sulfur content of increase in the composites, the charge and discharge specific capacity, coulomb efficiency and current density electrochemical performance of the sulfur cathode exhibited improvement and improve.(2) Because of insulating properties of sulfur and a mass discharge product of lithium polysulfide dissolved in liquid electrolyte, lithium polysulfide dissolved, loss and formation of the shuttle phenomenon is not only make the reduce of positive active materials, but also reaction with the negative metal lithium, affect the cycle properties of the lithium-sulfur battery. Therefore, in order to prevent loss and dissolved of polysulfide, further suppression Shuttle phenomenon. Add appropriate amount of LiNO3 in the sulfur-BP2000 composites, will reduce the loss and dissolved of lithium polysulfide. The experiment results indicated that the best addition amount was 1.0wt%.(3) The sulfur-BP2000 composites as a lithium battery cathode material in this paper, using lithium Nafion anion ion exchange membrane, in order to eliminate or decrease caused by dissolution of polysulfide lithium shuttle phenomenon. Furthermore, using V2O5 layered crystal structure, only allow Li+ embedded and emergence, in the battery film surface preparation of thin film with sol-gel technique methods, trying to prevent polysulfide lithium ions in the electrolyte. The experiment results indicated that use thin film materials which can prevent lithium polysulfide dissolved, loss and inhibition of charging and discharging process of oxidation-reduction shuttle phenomenon, improve the electrochemical performance of the lithium sulfur battery. And found 3:1 sulfur-BP2000 composites materials using Nafion membrane assembly lithium sulfur batteries, the electrochemical reaction indicated which the larger initial discharge specific capacity of 1031.45 mAh/g, after 25 cycles at 0.1 C?0.2C just 13.2%?17.2% fade.