Synthesis And Electrochemical Properties Of Multi-dimensional Carbon Based Cathode For Lithiu M Sulfur Batteries

Lithium-sulfur batteries(LSBs)are regarded as one of the most promising rechargeable energy storage systems,which have been pursued as an alternative to lithium ion batteries(LIBs)due to their ultrahigh theoretical energy density of 400 Wh kg-1 and have great application potential in the transportation,electronic information and national defense fields.However,the commercialization of sulfur cathode is severely hindered by fast capacity fading and low coulombic efficiency issues,which are caused by:(1)insulating nature of elemental sulfur and Li2S,leading to poor high rate performance;(2)large volume fluctuation during cycling,leading to poor electrode structure stability and low cycling performance;(3)the adverse "shuttle effect" caused by the dissolution and diffusion of reaction intermediate polysulfides will largely decrease the electrode performance.In such a context,appropriate steps must be taken to overcome these headwinds:carbon-based materials become the ideal host carrier for active sulfur due to their advantages such as good chemical stability,lightweight,high conductivity,large specific surface area,adjustable pore state and low-cost.The main research contents and results are presented below:(1)Inspired by a popcorn fabrication from corn raw,herein a unique porous macrocellular carbon composed of cross-linked nano/microsheets by a powerful puffing of rice precursor is described.The rice is directly puffed with a volume enlargement of about 20 times when it is instantaneously released from a sealed environment with a high pressure of 1.0 MPa at 200 ℃.Interestingly,when metal(e.g.,Ni)nanoparticles are embedded in the puffed rice derived carbon(PRC),high-quality PRC/metal composites are achieved with a surface area of 1492.2 m2 g-1.The PRC/Ni are employed as a host in LSBs.The designed PRC/Ni/S electrode exhibits a high reversible capacity of 1361.8 mA h g-1 at 0.1 C,a prolonged cycle life(813.1 mA h g-1 after 500 cycles),and enhanced rate capability.The excellent properties are attributed to the advantages of PRC/Ni network with a high electrical conductivity,strong adsorption/blocking ability for polysulfides,and interconnected porous framework.(2)Hierarchical porous spore carbon(SC)produced by Aspergillus oryzae is reported,which acts as a biofactory.Interestingly,the spore carbon not only shows a porous maze structure consisting of crosslinked nanofolds,but also is intrinsically N and P dual doped.Impressively,the spore carbon can be further embedded with Ni2O nanoparticles,which serve as porogen to form a highly porous spore carbon/Ni2P composite with increased surface area and enhanced electrical conductivity.To explore the potential application in LSBs,the spore carbon/Ni2P composite is combined with sulfur,forming a composite cathode,which exhibits a high initial capacity of 1347.5 mAh g-1 at 0.1 C,enhanced cycling stability(73.5%after 500 cycles),and better rate performance than the spore carbon/S and artificial hollow carbon sphere/S counterparts.The synergistic effect on suppressing the shuttle effect of intermediate polysulfides is responsible for the excellent LSBs performance with the aid of a physical blocking effect arising from the electrical maze porous structure and the chemical adsorption effect originating from N,P dual doping and polarized compound Ni2P.(3)A facile combined strategy is used to fabricate novel porous carbon fibers/vanadium nitride arrays(PCF/VN)composite scaffold for the storage of sulfur via a facile chemical etching united solvothermal-supercritical fluid method.More active sulfur can be stored in the PCF/VN backbone and dual blocking effects associated with "physical block and chemical absorption" for polysulfides are achieved in the PCF/VN/S integrated electrode.The PCF with highly porous structure provides large space to accommodate active sulfur and possesses cross-linked maze channels to physically immobilize the polysulfide species.The VN nanobelt arrays demonstrate strong ability for chemically anchoring the polysulfides,thus retarding the shuttle effect.Due to the unique structure and dual confining effect,the designed PCF/VN/S electrode shows a high reversible capacity of 1310.8 mA h g-1 at 0.1 C,an extended cycle life(1052.5 mA h g-1 after 250 cycles).Reversible capacities of 1310.8,724.1,and 591.6 mA h g-1 can be achieved for PCF/VN/S electrode at 0.1 C,2 C,and 5 C,respectively.