The Preparation And Electrochemical Performance Of The Cathode Material PMMA@S For Lithium Sulfur Batteries

The rapid development of portable electronic devices and electric vehicles for the lithium batteries to provide more energy.Lithium-sulfur batteries is the batteries whose cathode active material is sulfur,and oppose to lithium, the anode.Because of its large specific capacity(1675 mAh/g), high energy density (3500 Wh/kg), sulfur and environmental protection, low-cost advantage, lithium-sulfur batteries have had been keeping on investigating in recent years by many researchers.However, the low electrical conductivity of elemental sulfur and its discharge final products, the high solubility of the intermediate polysulfides results in the loss of active material and shuttle through both besides of separators and self-discharge, the large volumetric expansion (80%) upon lithiation gives rise to deteriorating cycle performance because of the different density, destroy electrode structure.The three difficult problems become the bottleneck of development of lithium sulfur batteries.In order to solve the above problems, this article on lithium-sulfur battery anode coated with polymethyl methacrylate (PMMA).In the third chapter, it expounds the methyl methacrylate (MMA) molecule carrying ester base for electronics, and when the polymerization reaction happens sulfate anion, these groups to electrostatic effect inhibit migration of polysulfide lithium on micro.On macro,PMMA which polymerizated from the monomer easily self-assembled nanoparticles.The nanoparticles layer has good fluid absorption.After the absorption,the the spread of the electrolyte of lithium-sulfur batteries will be further restricted.PMMA has the properties of photonic crystal,and coating PMMA forms a thin layer,it will emit the light of certain wavelengths by sunlight.For small size of PMMA, PMMA nanoparticles with 100～300 nm sizes will emit the light of wavelengths which is in the range of visible light.So, the light color PMMA coating layer reflected can be observed to quickly determine particle size of PMMA.In the third chapter, it expounds the preparation of small particle size of PMMA.And PMMA dilution dispersions are coated on the cathode of lithium-sulfur batteries (the cathode of lithium-sulfur batteries hereinafter referred to as "Sample S") by PMMA@ S electrode and assembling battery, inspects the PMMA is added to the performance influence.Through a series of electrochemical test found that PMMA@ S cycle performance are higher than S. No.3 small particle size of PMMA coating in S (Sample PMMA@S-A-200) on the cycle performance is the best. Sample PMMA@S-A-200 still more than three times of the Sample S’s specific capacity when batteries had stably cycled after 100 times.In addition, when the coating production carried,it implies the continuous rapid operation process.The mutual adaptation between the electrode preparation and the battery assembly process described in the second chapter is conducted.Finally, No.1 small particle size of PMMA dilution dispersion coating on the cathode of lithium-sulfur batteries (Sample PMMA@S-B-100) to increase the specific capacity of these batteries.Meanwhile, the charging-discharging test condition is improved in narrow electrochemical window (Sample PMMA@S-C-100), get the high specific capacity during the cycling and stability lithium sulfur batteries.To sum up, this article mainly expounds the following three aspects:(1) The monomer, MMA, polymerized with the little-sized PMMA particle. By controlling the concentration of monomer and initiator, it forms a series of particle size of PMMA nanoparticles with peroxydisulfate anion on its surface.(2) The production technology of lithium sulfur batteries are summarized.By the mutual adaptation of the electrode preparation and assembling battery continuous production process, PMMA dispersion liquid coating on lithium-sulfur battery cathode.So PMMA@ S has showed more significantly cycling performance than S.(3) The dilute PMMA dispersion is coated on cathode and the narrow electrochemical window is used in testing these batteries. Both of the two mathods make lithium sulfur batteries more stable charge-discharge cycle performance,and these batteries release higher specific capacity.