Preparation Of Porous Carbon Derived From Biomass And The Research And Application In The Cathode Of Lithium-sulfur Batteries

With the continuous development of science and technology,human shows more and more demand for the energy resources,and energy storage devices are increasingly being valued.Due to the limitation of theoretical capacity,the development of lithium ion battery is becoming bottleneck.Lithium-sulfur battery,one type of novel rechargeable batteries,with the highest theoretical specific capacity(1675 m Ah g-1)and energy density(2600 Wh kg-1).It's also low cost and environmentally friendly.Therefore,it is widely concerned by scientists.However,the lithium-sulfur battery is suffer from the low conductivity of its cathode and the “shuttle effect”,which means the intermediate product,dissolving easily in electrolyte during the electrochemical reactions,spontaneous reacts with the lithium anode.Biomass porous carbon materials are widely used as the cathode matrix of lithium-sulfur batteries due to their low cost and environmental friendly.Based on this background,we will report the different porous carbon materials which were prepared by different precursor via different activation methods in this paper.These porous carbon materials were used as matrix in the lithium-sulfur batteries.Hierarchical porous carbon materials,which were prepared from soybean hulls via KOH activation,have a wealth of pore structure.These materials have a high specific surface area of 1232 m2 g-1 and a large total pore volume of 0.5394 cm3 g-1,resulting in the 63.7 wt % loading of sulfur after mixing with via thermal treatment.The electrochemical performance tests show that the sulfur/porous carbon composites have an initial discharge capacity of 1231 m Ah g-1 at the 0.5 C rate.With orange peel as precursor,OGMC material prepared by zinc chloride activation has the advantages of convenient synthesis and low requirement of synthetic equipment.This material is rich in mesoporous and the specific surface area is up to 1508m2 g-1.The S/OGMC was prepared after mixing with sulfur via solution process and the S/OGMC/PPy composites were prepared via pyrrole in situ oxidative polymerization method.The loading of sulfur is 71.4%,which is measured with thermal gravimetric analysis.The S/OGMC/PPy composites have an initial discharge specific capacity of 1427 m Ah g-1 at 0.5C,after 200 cycles it still remains nearly 700 m Ah g-1 during electrochemical testing.However,the initial discharge specific capacities of S/OGMC and pure sulfur were 1338 and 1127 m Ah g-1,the remaining capacity were 470 m Ah g-1and 260 m Ah g-1 after 200 cycles,respectively.It means polypyrrole coating can improve the electrochemical performance for the cathode of lithium-sulfur batteries.In order to reduce the pollution caused by activation reagent,and reduce the collecting cost of biomass precursors,a novel mesoporous carbon material(Starbons)was prepared by self-assembly method with starch as precursor.The pore structure of Starbons was no less than OGMC material,which was proved with SEM,TEM and BET characterization,and its specific surface area was up to 1750m2 g-1.The elemental sulfur was filled into Starbons via solution method,and then the S/Starbons composite was coated with polypyrrole.The sulfur content was 70.1%.The electrochemical properties of S/Starbons/PPy composites are excellent,not inferior to S/OGMC.The initial discharge specific capacity of S/Starbons/PPy is 1395 m Ah g-1 at 0.5C,and it still remains 789 m Ah g-1 after 200 cycles.After 40 cycles of different rate test,its capacity can still be maintained at 890 m Ah g-1,exceeding its first discharge capacity of 70%.It proves that S/Starbons/PPy composites have excellent rate performance.