Preparation And Electrochemical Lithium Storage Properties Of S/C Cathode Materials

Along with the increasing demand for new energy-storage materials,Li-S batteries have been receiving increased attention because of their large theoretical specific capacity of 1675 mAh g^-1,low cost,abundant sources,nontoxicity,and environmental friendliness.Nevertheless,the practical application of Li-S batteries is still restricted by the low electrical conductivities of sulfur(5×10^-30 S·cm^-1 at RT),dissolution of lithium polysulphides that results in a shuttling effect,eventually leading to the loss of capacity and low coulombic efficiency.To mitigate the active materials loss and overcharge problem encountered in charge-discharge process of lithium-sulfur battery,this paper utilizes phenolic resin,low-cost agricultural wastes shaddock peel,chestnut shell as the precursor for the porous carbon to obtain S/C cathode composites.these composites were characterized by means of LAND battery tester?XRD?SEM?TEM?TGA and other techniques to represent morphology,structure and electrochemical properties of the materials.The experimental results are as follows:?1?With the phenolic resin as carbon precursor and element sulfur as sulfur precursor,S@PRPC composites was produced.Freeze-drying and thermal treatment of graphene oxide were employed to encapsulate S@PRPC composites in this study.The obtained graphene coated S@PRPC composites?S@PRPC/FD-rGO?were used as a Li-S battery cathode material.The results show that when the hexamine content is 12%,carbonized temperature is 850?,the sulfur content is 60%,the S@PRPC composites of the best performance display a capacity at 912.2 m Ah g^-1 and remains35.5%after 100 cycles,while the first discharge capacity of the S@C/FD-rGO composites displays a capacity at 965.8 m Ah g^-1 and remains 50.6%after 100 cycles.When tested at the current density of 0.5 C,the composites displays a capacity at449.4 mAh g^-1 with the 99.0%coulombic efficiency.The graphene coating nanostructure can restrain the dissolution of polysulfide effectively and improve the electrochemical performance of the S@PRPC composites obviously.?2?The strategy utilizeslow-cost agricultural wastes,shaddock peel as the precursor and inexpensive ZnCl₂ as the pore-foaming agent for the 3D porous structure of the resultant composite.As confirmed by a higher temperature thermal treatment,the sulfur nanoparticles were homogenously distributed in SPPC matrix.The results show that when the ZnCl₂ content is 75%,carbonized temperature is1000?,the sulfur content is 60%,the S@SPPC composites of the best performance exhibited a high capacity retention of 81.1%at 1 C after a long-term cycling of 500cycles,showing an excellent cycling stabilities at high rate.Even at a larger rate of 2C and 3 C,the composite can retain a high capacity retention of 84.4%and 62.7%,respectively.Such an excellent cycling stabilities and high rate capabilities should be attributed to the unique 3D network structure with a high specific surface area and large pore volume of SPPC,which can not only adsorb the soluble polysulphide intermediate product,but also allow both Li⁺and electron transport efficiently.?3?In this study,the bio-based technique was chosen and chestnut shell was taken as the raw material creatively to prepare the 3D porous carbon through a simple thermal carbonization followed by ZnCl₂ activation.The results show that when the ZnCl₂ content is 75%,carbonized temperature is 1000?,the sulfur content is 60%,the S@SPPC composites of the best performance exhibited a high capacity retention of 75.9%at 0.5 C after 200 cycles,showing an excellent cycling stabilities at high rate.Even at a larger rate of 2 C and 3 C,the composite can retain a high capacity retention of 72.6%and 65.1%after 400 cycles,respectively.