Controlling The Structure Of Shaddock-peel Derived Carbon Materials As Anodes For Improved Lithium/Sodium Storage Performance

Biomass-derived carbon materials are considered as a group of very promising anode materials for lithium/sodium-ion batteries because of their naturally diverse and intricate microarchitectures,adjustable physical/chemical properties,abundant sources,environmental friendliness and low cost.However,the relatively rare storage sites and low diffusion kinetics of biomass-derived carbon materials result in poor cycling stability and rate performance.This paper selects the shaddock peel as the precursor and develops a strategy that controlling the pseudographitic structure,surface functional groups,and heteroatoms doping structure of shaddock peel-derived carbon boosting its storage sites and diffusion kinetics,aming to simultaneously improve the cycling stability and rate performance.Furthermore,the cooperative regulatory mechanism of pseudographitic structure,surface functional groups,and heteroatoms doping structure has been explored,the mechanism of electrochemical reaction has been clarified,the mechanism of improving cycling stability and rate performance has been revealed,and the model of shaddock peel-derived carbon structure,Li+/Na+storage mechanism and electrochemical performance has been established,which further improve the electrochemical performance and broadens the practical application field of shaddock peel-derived carbon.The main innovations are shown as follows:(1)The shaddock peel-derived carbon materials surrounded by different thicknesses of pseudographitic domain were prepared by a simple hydrothermal method with following carbonization process.The thickness of pseudographitic domain can be designed effectively via controlling different pyrolysis temperature,which could improve the diffusion kinetics with sufficient Na+storage sites.The relationship among adsorption sites,diffusion rate and electronic conductivity is also balanced.When used as anode materials for SIBs,the shaddock peel-derived carbon materials with a pseudographitic domain thickness of 7.3 nm exhibite a high capacity of 287.3 mAh g-1 at 50 mA g-1,retaining a reversible capacity of 89 mAh g-1 at 5000 mA g-1,and showing a capacity retention of 87%after 500 cycles.(2)The shaddock peel-derived carbon materials with abundant carbon-oxygen double bond(C=O)and highly ordered pseudographitic structure were synthesized through a H2SO4-assisted hydrothermal pretreatment and subsequent KOH-assisted low temperature pyrolysis procedure.By adjusting the pyrolysis temperature and activator ratio,the C=O functional groups on the surface of shaddock peel-derived carbon materials could be increased,and the graphitization degree of pseudographitic structure could be enhanced,thus boosting the Na+ storage sites and diffusion kinetics.When the ratio of hydrothermal carbon to KOH is 1:1,the sample pyrolyzed at 600℃(SP34)delivers excellent cycling and rate performances in sodium-ion batteries,delivering a high reversible capacity of 380 mAhg-1 at 50 mAg-1 after 500 cycles,and that of 274 and 199 mAhg-1 even at 500 and 1000 mAg-1,respectively.(3)S-doped(2.8 at%)shaddock peel-derived carbon materials(KPP-SDC)were prepared by a KOH and C2H5NS assisted pyrolysis procedure.The covalent C-S bond can effectively increase the active storage sites,reduce the adsorption energy,promote the graphitization degree,and enhance the ability of e-transport and Li+diffusion.Moreover,thiophene S can enlarge the interlayer spacing and avoid the volume expansion during the cycling process.Thus,the surface adsorption capacity and electrochemical kinetics of shaddock peel derived carbon materials were enhanced by S doping.The KPP-SDC exhibits a high reversible capacity of 738 mAh g-1 at 50 mA g-1 after 200 cycles,and 492 mAh g-1 at 200 mA g-1 after 300 cycles.Even at 1000 and 2000 mA g-1,the KPP-SDC can still afford a high rate capacity of 283 and 179 mAh g-1,respectively.Besides,it is revealed that the Li+ storage process depends on the surface-induced pseudocapacitive behavior with a capacitive contribution up to 60%at 0.5 mV s-1.(4)N-doped(4.7 at%)shaddock peel-derived carbon materials(N-d-SPC)were successfully synthesized by alkali activation and carbamide-induced N-doping procedure.Different C-N network structures were constructed in the process of N doping,which greatly promoted the Li+storage and electrochemical kinetics.Pyrrolic-N could enlarge the interlayer distance,pyridinic-N and pyrrolic-N could produce abundant adsorption and insertion storage sites,graphitic-N could improve the e-transport.N-d-SPC electrode affords high cycling and rate capacities with the reversible capacity of 673 mAh g-1 after 100 cycles at 50 mA g-1,and 282 and 172 mAh g-1 even at 2000 and 5000 mA g-1,respectively.Furthermore,the main electrochemical reaction mechanism of N-d-SPC electrode is the surface electrochemical induced capacitance process,followed by the diffusion process,especially at high current density.The N-d-SPC electrode demonstrates a pseudocapacitive contribution of 73%at 0.5 mV s-1,which results in the surface electroadsorption predominant Li+ storage with a capacity contribution of 63%at 50 mA g-1.