Improving Electrochemical Performance Of Lithium-Sulfur Barreries By Chitosan

Due to the high energy density and discharge specific capacity, lithium-sulfur battery is expected to become the next generation of secondary battery. However, the poor cycle performance and low utilization of active material hinder the commercialization of the lithium-sulfur battery. One of the most reasons is that the polysulfide dissolves into electrolyte easily during the charge-discharge process. In this work, the influence of the chitosan on trapping the polysulfides in the charge/discharge process and improving the electrochemical performance of the lithium-sulfur batteries have been researched, which can be attribute to the varies functional groups such as amino and hydroxyl.Firstly, chitosan has been used as an additive in the cathode to improve the electrochemical performance of lithium-sulfur battery. The cathode with chitosan shows improved discharge specific capacity and cycle performance. At C/10, the initial discharge specific capacity of the cathode with chitosan is 1145 mAh/g and the reversible capacities after 100 cycles reach to 680mAh/g, 647mAh/g at respectively, C/2 and 1C rates. Chitosan can trap and activate the polysulfide which dissolves into the electrolyte increasing the utilization of the active material.Then, in order to putting forward the polysulifide absorption of the chitosan, a composite separator with chitosan as the sorbent and super thin-film carbon coating is presented and the thickness of the coating is only 1.5μm. Through the structure and electrochemical analyses, the composite separator can suppress the "shuttle effect" improving cycle performance. Cells with modified separator achieve the initial capacities of 1158 mAh/g,837 mAh/g and 834 mAh/g at respectively, C/5, C/2 and 1C rates. After 100 cycles the capacity approach 830 mAh/g at C/2. When the cycle number is increased to 200 at 1C, the reversible capacity of the cell with modified separator can approach 675 mAh/g.At last, the ac-impedance spectra were used to research the discharge process of the lithium sulfur batteries. It has been proved that the electrolyte resistance, surface film resistance and charge-transfer resistance at all depths of discharge can be effectively decreased by using chitosan as an additive, which is benefit for the improvement of the electrochemical of the lithium sulfur batteries.