Investigation On Preparation And Electrochemical Performance Of S-C Cathode Material Coated By Conductive Polymer

The enormous demand for energy provides a broad prospect for energy storagematerials. Li-S battery becomes the most promising lithium battery system because it’stheoretical capacity is very high(1675mAhg-1). However, its inherent low conductivityand the intermediates polysulfide of electrode reaction freely tending to dissolve inelectrolyte and the volume change in the progress of charging and discharging whichlimits its good electrochemical performance under high discharge rate when sulfurserves as cathode material. Recent research shows that the coated structure cathodematerial not only can improve ion and electron conductivity, limit the dissolution oflithium polysulfide, but also slow down the influence of volume change. Therefore, thisstudy prepares the coated structure S-C-PPY and S-C-PANI cathode material based onthe coated structure idea. Characterize its structure, morphology and electrochemicalperformance. Finally, discuss the reason of the improvement of electrochemicalperformance.This paper prepares the coated structure cathode material by using two-stepmethod. The first step is that acetylene black is coated on the surface of sulfur. Thesecond step is that PPY or PANI is coated on the surface of S-C cathode material. It isS-C-PPY and S-C-PANI cathode material. The experiment synthesises a series ofcathode material by adjusting the king of surfactant, the hydrochloric acid concentrationin the polymerization process, the amount of polymer, the sulfur content. Characterizeand analysis its structure, morphology and electrochemical performance to find the bestsynthesis step of S-C-PPY and S-C-PANI cathode material.The characterization of morphology and structure shows the experimentsynthesises double layer coated structure cathode material when ethanol and CTABserve as surfactant in the first and second step. Sulfur exists interior, and the outer layeris polymer. Their intermediate is acetylene black. Particle presents globular and the sizeis micron order. Electrochemical performance characterization shows that thepreparation condition of the best electrochemical performance is that the hydrochloricacid concentration in the progress of polymerization is0.5mol/L and the molar ratio ofoxidant: pyrrole is3:1. the content of sulfur and PPY is40%and4%. At1C rate, the discharge capacity is768mAhg-1in the first cycle and maintain326mAhg-1over500cycles. The decay is very slow(0.115%per cycle after500cycles) and coulombefficiency is over90%per cycle. The prepare condition of the best electrochemicalperformance is that the hydrochloric acid concentration is1mol/L in the progress ofpolymerization and the molar ration of oxidant: aniline is3:1. the content of sulfur andPANI is45%and19%. The electrochemical performance characterization shows thatthe discharge capacity is809mAhg-1and507mAhg-1in the first cycle at1C and2Crate. After1000cycles, the discharge capacity maintain271mAhg-1and217mAhg-1,and the cyclic degradation rate is0.066%and0.062%. The coulomb effienciency isabove90%. Comparing electrochemical performance S-C and S-C-PANI cathodematerial that they was synthesized in the same condition, the conclusion shows theelectrochemical performance of S-C-PANI is batter than S-C cathode material. Amongthe reason for it is that double layer coated structure of acetylene black and polymerimproves the conductivity of cathode material, limits the dissolution of lithiumpolysulfide and slows down the influence of volume change.