Novel Carbon And Bismuth Materials: Design,Preparation And Sodium Storage Performance

With the advantages of high specific capacity,high working voltage and long cycle life,lithium-ion batteries have been widely used in notebook computers,mobile phones and electric vehicles after decades of development.However,it is difficult to meet the market's demand for high energy density and power density energy storage devices because of the limited lithium resources and high costs.At the same time,sodium-ion batteries have sprung up because it has a similar storage mechanism compare with lithium-ion batteries.More importantly,the earth has abundant sodium resources and its cost is low,which makes sodium ion batteries have the potential for further research and broad application prospects.However,because the radius of sodium ion is 0.102 nm(55%larger than that of lithium ion),which makes it difficult for materials previously applied to lithium ion batteries to be directly applied to sodium ion batteries.Therefore,we are committed to researching and developing suitable materials to realize the commercialization of sodium ion batteries.Here,a kind of hollow tremella-like carbon spheres assembled with two-dimensional nanosheets are prepared by hydrothermal method and carbonization treatment.At the same time,Friedel-Crafts reaction and carbonization treatment are applied to obtain carbon foam with three-dimensional honeycombs.Finally,a novel one-step carbonization method was designed to obtain Bi@C.The specific research content is as follows:(1)Hollow tremella-like carbon spheres(HTCS)are obtained through hydrothermal reaction using silicon dioxide,nickel acetate and gluconic acid as raw materials.At the same time,the nickel silicate formed during hydrothermal reaction will be decomposed into nickel and silicon dioxide in the next heat treatment,and the nickel will promote the graphitization of the carbon nanosheets,thereby obtaining a structure in which the graphite nanoribbons are intertwined in the amorphous framework.When employed HTCS as anode in sodium ion batteries,it is interesting to find that the ordered graphite nanoribbons can simultaneously serve as“bandage”to protect amorphous carbon region from crack and pulverization upon the sodiation/desodiation processes and offer electron immigration pathways to improve the electrode conductivity.Consequently,HTCS presents superior sodium storage performance.It can deliver a high reversible capacity of 278 m Ah g^–1 at 0.1 A g^–1 after 100 times,and maintain a remarkable capacity of 142 mAh g^–1 after repeated charge/discharge for 1000times at 1 A g^–1,indicating a very low capacity loss of 0.02%per cycle.More importantly,HTCS has impressive high rate capability,for example,even under a very high current density of 10 A g^–1,it retains a large capacity of 146 m Ah g^–1,giving capacity retention of 68%against the capacity under 0.05 A g^–1,which is superior to most of current hard carbon anodes.(2)We report a novel method to synthesize carbon foam with three-dimensional cross-linked pores by direct cross-linking of styrene-butadiene rubber-based powder puff.The high-density cross-linking bond constructed by the cross-linking reaction can solve the thermal instability of styrene butadiene rubber,and endow SBR with rigid macromolecular framework and carbonizability.The obtained carbon foam has light weight,well-developed honeycomb-like pore structure and superior high-temperature stability,and presents superior oil-water separation performance and Na⁺storage property.The obtained carbon foam has high adsorption capacities of pump oil and other solvents(300?500%),and it can be recovered to the original state by combustion.In addition,carbon foam exhibits good reversible Na⁺storage capacity and can give a capacity of 220 m Ah g^–1.(3)Ammonium citrate is selected as raw material to fabricated Bi@C composite doped with nitrogen by heat treatment.The structure of Bi@C possesses the following advantages:(i)the thin carbon layer coated on the Bi particle is in favor of forming stable SEI film and accommodating the volume expansion of Bi during the cycling process;(ii)the nano-sized Bi particles with the diameter around 15 nm cut down the strain originated from the sodiation/desodiation process and enhance the rate performance.Benefiting from the above merits,Bi@C presents excellent rate capability and superior cycling performance.It can deliver a capacity of 346 m Ah g^–1 after 130 cycles at 0.1 A g^–1.Even under the large current density of 1 A g^–1,it can still maintain a capacity of 344 m Ah g^–1.Even better,Bi@C exhibits ultrahigh rate performance,which delivers a satisfactory capacity of 274 m Ah g^–1 even under the current density of 50 A g^–1 with high capacity retention of 85.9% against the capacity under 0.05 A g^-1.