The Electrochemical Performance Of Room Temperature Sodium-Sulfur Secondary Battery

Room-temperature sodium-sulfur batteries?RT Na-S?are gaining much more attention as a high energy density and low-cost option for large-scale electrical energy storage application.However,the insulation of elemental sulfur and the solubility of polysulfide may lead to poor cycling life,low coulombic efficiency and reversible capacity,which are main challenges for RT Na-S.Due to excellent electric conductivity,large specific surface area,rich microporous and nature abundance,carbon-matrix composites with sulfur have become potential cathode material.As a promising electrolyte additive,vinyl ethylene carbonate?VEC?is in favor of forming of a stable SEI and reducing effectively the polysulfide shuttle,thus increasesing the electrochemical performance.In this paper,we used carbon materials and sublimed sulfur to prepare the composites materials as cathode material,and chose VEC as an electrolyte additive which can effectively improve the electrochemical performance of RT Na-S.Firstly,cathode material was synthesized by YP-50 F carbon material and sublimed sulfur,the electrolyte was composed of 1M NaClO₄?EC: PC=1:1 v/v?and different amount of VEC.The result shows that the capacity of RT Na-S battery with VEC electrolyte is significantly improved,and the discharge capacity is increased from 936 mAh g^-1 to 1650 mAh g^-1.It means that the addition of VEC is conducive to the formation of SEI,which avoids the polysulfide shuttle and increases the capacity of RT Na-S battery.Secondly,we compared the electrochemical performance of electrolytes with different amount of VEC addition,the results indicated that the capacity of RT Na-S battery is improved at the first 40 cycles,which is suffice to prove that SEI can effectively inhibit the polysulfide shuttle.But the electrolytes with different amount of VEC addition result in different cycling stability: the electrolytes with 3% VEC addition significantly improved capacity and cycling stability,corresponding to a capacity retain of 84.6% after 100 cycles;and the electrolytes with 1% and 5% VEC addition exhibited much higher capacity decay after 40 cycles,corresponding to a capacity retain of 28% and 30% after 100 cycles,respectively.Finally,we compared the electrochemical performance of different composites materials synthesized with different carbon materials.Carbon/sulfur composites were synthesized by two kinds of carbon material?YP-50 F and XFP01?compound with sublimed sulfur as cathode materials,and the electrolytes with 3% VEC addition.The result shows that the reversible capacity of YP-50F-S and the XFP01-S composite was 1651 mAh·g^-1 and 1450 mAh·g^-1,respectively.But the reversible capacity of XFP01 is higher than yp-50 F.It means that the nature of carbon material has great influence on the electrochemical performance of RT Na-S.