Study On The Controllable Construction Of Honeycomb Carbon In-situ Grown Nano-energy Storage Materials And Their Lithium Storage Properties

Human society is facing the shortage of fossil energy.It is urgent to develop a stable and high specific capacity electrochemical energy storage devices（EESDs）.As a new type of energy,lithium ion batteries（LIBs）have the characteristics of high energy density and large operating voltage,occupying most of the EESDs market.At present,LIBs with graphite as anode material have high conductivity and strong stability,but due to the low theoretical capacity(372 m Ah g^-1),it is necessary to develop new high-capacity anode materials.Conversion reactive materials（Fe₃O₄,CoSe）and Prussian blue analogues（Fe-CoPBA）are considered to be promising anode materials for lithium ion batteries due to their high theoretical specific capacity,low cost and low pollution.However,serious volume change and low electronic conductivity are great challenges for them.In order to solve the above problems,honeycomb carbon@Fe₃O₄ hollow nanospheres,honeycomb carbon@nano-CoSe,and honeycomb carbon@nano-Fe-CoPBA were synthesized in this paper.Based on the nanostructure design and high-conductivity honeycomb carbon composite strategy,their lithium storage performance was improved.The main research contents are as follows:（1）Polystyrene（PS）spheres were prepared by chemical polymerization.PVP and Fe（NO₃）₃ were dissolved in PS sphere emulsion using PS spheres as templates.The dense assembly precursor of Fe（NO₃）₃@PVP@PS spheres was synthesized by solution controlled evaporation.Finally,3D honeycomb carbon@Fe₃O₄ hollow nanospheres composites（HC-C@HS Fe₃O₄）were prepared by one-step calcination.SEM,TEM,Raman and other material characterizations show that Fe₃O₄ hollow nanospheres with a diameter of 10-16 nm grow in situ on the inner surface of each macroporous（pore size of about 200 nm）of 3D honeycomb carbon.3D honeycomb pores construct a large number of closed spaces for Fe₃O₄,and honeycomb carbon is amorphous carbon formed by PVP decomposition.HC-C@HS Fe₃O₄ exhibits ultra-high specific capacity as an anode material for LIBs,with an average discharge capacity of 1618 m Ah g^-1 at 0.1 A g^-1.It delivers a discharge capacity of 770 m Ah g^-1 after 1000 cycles at a current density of 1 A g^-1,and a discharge capacity of 429 m Ah g^-1 after 200 cycles at a current density of 5 A g^-1.Kinetic analysis shows that the electrochemical reaction of HC-C@HS Fe₃O₄has a high proportion of capacitance effect and low electrochemical reaction impedance.The excellent lithium storage performance is due to the good structural effect of Fe₃O₄hollow nanospheres and honeycomb macroporous carbon.The in-situ growth of Fe₃O₄hollow nanoparticles can bring more active sites to increase the electrochemical performance.Honeycomb carbon can bring excellent conductivity and sufficient internal space.HC-C@HS Fe₃O₄ is an excellent anode material for lithium ion batteries.（2）The Co（NO₃）₂@PVP@PS sphere compact assembly precursor was prepared by a similar method（replacing Fe（NO₃）₃ with Co（NO₃）₂）,and then CoSe nanoparticles（HC-C@CoSe）were in-situ grown on the inner surface of each pore of three-dimensional honeycomb carbon by calcination and gas-phase selenization.The sizes of CoSe and honeycomb holes are 10-15 nm and 190 nm,respectively.Through thermogravimetric calculation,the content of CoSe is 72%（mass ratio）.When applied to LIBs anode materials.HC-C@CoSe has excellent cycle performance(823.5 m Ah g^-1 after 200 cycles at a current density of 0.5 A g^-1,610.1 m Ah g^-1 after 250 cycles at a current density of 2 A g^-1,247 m Ah g^-1 after 1500 cycles at a current density of 5 A g^-1)and rate capability(261.9 m Ah g^-1 at a current density of 10 A g^-1,1491.4 m Ah g^-1at a current density of 0.1 A g^-1).The good lithium battery performance of HC-C@CoSe is due to the nano-sized CoSe can provide more reaction sites,and the honeycomb carbon improves the electron conductivity and accelerates the electrolyte penetration and storage.The synergistic effect of the two enhances the reaction kinetics;the closed pore structure of honeycomb carbon effectively locks CoSe and improves the cycle stability of CoSe.The excellent electrochemical performance proves that HC-C@CoSe is a potential high-performance LIBs anode material.（3）The dense assembly precursor of Co（NO₃）₂@PVP@PS spheres was prepared by a similar method as above.After controllable calcination and then treated with potassium ferricyanide solution,a composite material（HC-C@Fe-CoPBA）with in-situ growth of Fe-CoPBA nanoparticles in the pores of three-dimensional honeycomb carbon was synthesized.The size of Fe-CoPBA is 20 nm,the diameter of honeycomb carbon pore is about 200 nm,and the thickness of carbon wall is 30-50 nm.The three-dimensional honeycomb carbon provides sufficient growth space for loading Fe-CoPBA.HC-C@Fe-CoPBA exhibits excellent cycle performance as an anode material for LIBs.It has a reversible capacity of 950 m Ah g^-1 after 200 cycles at a current density of 0.5 A g^-1,a reversible capacity of 657 m Ah g^-1 after 1000 cycles at a current density of 1 A g^-1,a reversible capacity of 496 m Ah g^-1 after 450 cycles at a current density of 2 A g^-1,and a capacity of 327.7 m Ah g^-1 at a rate of 5 A g^-1.The excellent lithium storage performance is mainly due to the organic combination of nano-Fe-CoPBA and honeycomb carbon.Nano-Fe-CoPBA particles have more active sites.Honeycomb carbon can improve the conductivity of PBA and provide space for the volume expansion of Fe-CoPBA during charging and discharging.It also facilitates the diffusion of electrolyte.The synergistic effect of these favorable factors significantly improved the electrochemical performance of HC-C@Fe-CoPBA.