Research On The Effects Of Additives On Electrochemical Performance Of Lithium Sulfur Batteries

The theoretical specific capacity of lithium-sulfur(Li-S)batteries are 1675 mAh g-1,and sulfur is cheap and environmentally friendly,Li-S batteries gradually develop into one of the high energy storage battery system in recent years.As research continues,some problems of Li-S batteries gradually exposed: on one hand,the poor electrical conductivity of S and Li2S2/Li2 S make the impedance of Li-S batteries are larger;on the other hand,parts of the charging and discharging products(polysulfide)are easily dissolved in the electrolyte,which cause the alleged "shuttle effect",the effect could cause the lose of the positive electrode actives,and the cycle performance of Li-S batteries will fall.In order to solve the main problems of Li-S batteries,a certain amount of mesoporous molecular sieve SBA-15 with larger pore size was added into the sulfur electrode to absorb the lithium polysulfides and inhibit the "shuttle effect".The physical characterization indicates that SBA-15 has adsorption to lithium polysulfides,electrochemical performance tests indicate that the cell with 1% SBA-15(SCS-1)shows excellent cycle performance and rate performance.After 300 cycles,the specific discharge capacity of SCS-1 cell was 200 mAh g-1 higher than that of the cell without SBA-15(SCS-1).As a result of the poor electrical conductivity of SBA-15,the electrochemical performance of the cell with 1.5% SBA-15(SCS-1.5)was not so good,for adding too much SBA-15 will increase resistance.Hence,adding 1% SBA-15 into sulfur electrode is beneficial to inhibit the shuttle effect of lithium polysulfides and the improvement of the electrochemical performance of lithium sulfur batteries.Platinum(Pt)is a commonly used catalyst in fuel cells,and sulphur and oxygen belong to the same main group in the periodic table and are much alike in chemical properties.Herein,a certain amount of platinum/carbon(Pt/C)material has been added into sulfur electrode to investigate the electrocatalysis on sulfur electrode in Li-S batteries.The electrocatalysis of Pt accomplished through the absorption between Pt and sulfur or Li2S2/Li2 S,and then makes the convertion between them more easily in the charge and discharge processes.Besides the addition of could increase the electrical conductivity of sulfur electrode and reduce the resistance.The electrodes with Pt show excellent specific capacity and cycling stability,the electrode with 2 wt.% Pt(SCP-2)has shown a 61% enhancement in the specific capacity over the electrode without Pt(SC)after 200 cycles with an average Coulombic efficiency of 98.3% at a rate of 0.5 C.