Preparation And Sodium Storage Performance Of Carbon Materials Derived From Spring Onion Peels

Upon the energy crisis and the environmental pollution,development of renewable energy and the high-performance energy storage devices has attracted enormous attention.Among numerous battery systems,sodium-ion batteries(SIBs)are acknowledged to be one of the most promising candidates due to low cost and abundance of sodium reserves.Therefore,developing anode materials with high capacity,long cycling life and excellent rate properties is paramount for the real-life applications of SIBs.Among currently reported negative materials,carbon materials have been considered as the most promising candidates because of their low cost,low sodium embedded platform and superior thermal stability.In order to find out a high cost-effective carbon anode material,a series of carbon materials with different structures were prepared using low-cost natural biomass(spring onion peel,SOP)as precursor through appropriate preparation methods.The effects of carbonization temperature,preparation method and heteroatom doping on the structure,morphology and sodium storage performance of carbon materials were systematically studied.The specific research contents are as follows:Firstly,three-dimensional porous hard carbon materials(HCN)were prepared by a one-step pyrolysis method with SOP as carbon precursor.The HNC samples effectively solved the problem of poor rate and cycle performance of traditional hard carbon materials in the application of SIB,due to its three-dimensional porous structure.A series of hard carbon with different microcrystalline graphite structures were obtained by adjusting the carbonization temperature(900-1300°C).And the effect of temperature on the microstructure and sodium storage properties of hard carbon were studied.It is found that HCN has better performance of sodium storage in ether-based electrolyte through the comparison between ester-based electrolyte and ether-based electrolyte.Among them,the HCN-1100 sample afforded an ultrahigh reversible capacity of 323.3 m Ah g^-1 at 50 m A g^-1,high rate performance177.4 m Ah g^-1 at 2 A g^-1,and long-term cycling stability at 5 A g^-1(?96%retention upon 2000 cycles).In order to further improve the rate performance of carbon materials derived from SOP,three-dimensional hierarchical porous framework of carbon nanocages(FCNC)and hierarchical porous carbon nanosheets(HPCN)were prepared by a one-step strategy,using KMn O₄ and Zn(NO₃)₂ as activators,respectively.As the templating and activation process occurring simultaneously,the products possess large effective specific surface area(SSA),favorable hollow structure and appropriate graphitization degree.As a result,specific capacitances as high as 490.7F·g^-1 at 1.0 A·g^-1 in a three-electrode capacitive system and energy density as high as 92 Wh·kg^-1 at a power density of 1,800 W·kg^-1,and 60 Wh·kg^-1 at 36,000 W·kg^-1using 1-ethyl-3-methylimidazolium tetrafluoroborate(EMIMBF₄)as electrolyte when applying FCNC in supercapacitors.Excitingly,FCNC also showed an excellent performance for SIB:a specific discharge capacity of 318.2 m Ah·g^-1 has been obtained at a current density of 50 m A·g^-1,which can be retained to 81.6m Ah·g^-1 at a current density of 10 A·g^-1 together with a high cycling stability(only7.5%capacitance loss over 1000 cycles at 10 A·g^-1).By comparing carbonate electrolyte with glycol dimethyl ether electrolyte,it is found that FCNC material has better sodium storage performance in ether electrolyte.Moreover,the as-prepared HPCN performed outstanding rate and cycling performances in SIBs.A specific discharge capacity of 309.2 m Ah·g^-1 has been obtained at a current density of 50m A·g^-1,which can be retained to 95.2 m Ah·g^-1 at a current density of 10 A·g^-1together with a high cycling stability(?97%retention upon 8000 cycles at 10 A·g^-1)The electrochemical performance of carbon materials can be effectively improved by heteroatom doping strategy.Sulfur doped three-dimensional porous carbon nanosheets(S-CNS)were prepared by a one-step method using SOP as carbon source and sulfur powder as sulfur source.The method has the advantages of low cost,simple process,green raw materials and easy access.The results showed that sulfur doping can not only create more active sites,but also expand the interlayer spacing of carbon materials,which is conducive to the insertion and desorption of Na⁺and achieve excellent sodium storage performance.Consequently,the resultant S-CNS product delivers an ultra-high reversible specific capacity(50m A·g^-1,605.5 m Ah·g^-1),excellent rate performance(10 A·g^-1,133.3 m Ah·g^-1)and excellent cycle stability(retention rate 94%after 2000 cycles at 5 A·g^-1).Moreover,combined with theoretical calculation,it is also shown that S-doping can effectively improve the sodium storage performance of the carbon material,and the in-situ C-S bond has displayed excellent adsorption effect on the polysulfide,which plays a key role in improving the rate and cycling performance of the carbon material.Moreover,we demonstrate that,S-doped carbon products with competent electrochemical properties for SIBs can not only be derived from SOP by this simple doping method,but also from a variety of other biomass.This work thus introduces a fertile ground to produce powerful electrode materials by using the mixture of biomass and S powder,which may hold considerable potential for scalable production of commercial SIBs.On this basis,in order to further increase the surface-controlled capacity and improve the rate performance of the S-doped materials,the sulfur doped three-dimensional hierarchical porous nanosheets(S-HPCN)was prepared by activating and doping method.The obtained carbon materials show excellent rate performance of which the specific capacity can reach 210.0 m Ah·g^-1 at a current density of 20 A·g^-1.