The Micro/nano Structure Controlling Of Sulfides And Their Electrochemical Performance

With the continuous and never-ending industrial development of electric vehicles(EVs),human society will demand a lot more of manufacturing lithium-ion batteries(LIBs)than before.However,the shortage of lithium resources,which has given rise to high cost,is still a hurdle for large-scale industrial applications of lithium-ion batteries.Therefore,it is becoming more and more important to develop a new rechargeable battery.Sodium-ion batteries(SIBs)are considered to be a promising substitute for LIBs due to their lower cost,rich natural resources and similar operating principles.Recently,metal sulfides have drawn a great deal of attention on account of their excellent chemical,physical,electrical properties,etc.Metal sulfides have been as an anode material for sodium-ion batteries due to their high theoretical capacity.On the basis of practical applications,metal sulfides confront many problems,for example,the pulverization trouble aroused by the volume expansion during charge-discharge process and the dissolution of the polysulfide intermediates in organic electrolytes will bring about a rapid capacity fading during cycling.At present,scientists propose two solving paths in order to overcome the above-mentioned troubles,one strategy is to design metal sulfides with nanomaterials,and the other is to fabricate metal sulfides with carbonaceous materials.The following is the primary research of this academic paper.(1)We fabricated CoS2/rGO composite via a facile one-pot solvothermal method,and investigated their electrochemical sodium storage as sodium ion batteries anodes.Taking a series of characterization measurements of the prepared samples,we can conclude that the CoS2/rGO composite is comprised of flakeswith a size range from 1 to 2 μm and CoS2 nanoparticles with a size range from 20 to 30 nm are anchored uniformly on the rGO sheets,which is substantially different from the bulky CoS2.It is obvious cycling performances that CoS2/rGO electrode shows better cycling stability than that the bare CoS2 electrode at a current density of 0.5 A g-1.After cycling 150 cycles,an improved reversible capacity of 250.8 mA h g-1 can be maintained for CoS2/rGO.By contrast,cycling the same cycle,the reversible capacities of 5.3 mA h g-1 are kept for bare CoS2.What’s more,a long-term cycle test was performed at a current density of 1 A g-1.And after cycling 1000 cycles,the reversible capacity still keeps 192 mA h g-1 with a high coulombic efficiency of 100%.As a result of the synergistic effect of CoS2 and rGO,CoS2/rGO as an anode material for sodium-ion batteries will fully embody an improved electrochemical performance in terms of specific capacity,cycling stability and rate capability.(2)Urchin-like Bi2S3/rGO composite were prepared by a simple solvothermal method,and their electrochemical performances were explored in sodium-ion batteries for the first time.From the characterization results of the samples,the panoramic image of the Bi2S3/rGO composite is presented urchin-like microsperes with an average diameter of about 4 μm and the microspheres are composed of nanorod with a diameter approximately 40 nm.The Bi2S3/rGO urchin-like microsperes,different from the Bi2S3 microsperes,are fairly uniform in size and shape.According to the analysis of the electrochemical tests,the Bi2S3/rGO composite exhibits more static cycle life and higher reversible capacity.Specifically,the Bi2S3/rGO composite achieves a higher reversible capacity of 370.1 mA h g-1 at a current density of 100 mA g-1 after cycling 50 cycles,which is much better than the acquired capacity(40.6 mA h g-1)of the Bi2S3 electrode under the same conditions.The excellent electrochemical performances of the Bi2S3/rGO composite are attributed to two reasons,one reason is the Bi2S3 inherit a high theoretical capacity of 625 mA h g-1 in the Bi2S3/rGO composite,and the other is that the graphene not only is a conductive matrix speeding up the electron transport but also serves as a tough buffer restricting the volume expansion of the Bi2S3 during the charge-discharge process.