Fabrication And Research On The Sodium Storage Properties Of Hollow Mesoporous Carbon Nanospheres And Hierarchical CuO Nanocubes

Since the advent of lithium-ion batteries(LIB_S),it has achieved rapid development and widely occupied the battery application market.However,limited lithium resources and high price directly restrict the long-term development of the LIB_Sin the future.Sodium ion batteries(SIB_S)are a sort of low-cost alkali metal ion batteries with the advantage of abundance and cheapness of sodium resources.As a possible alternative product of lithium ion batteries,SIB_Shas attracted a lot of attention from researchers in recent years.SIB_Sis very attractive for large-scale energy storage,such as power grids,which do not require large volume or mass energy density.However,the large Na⁺radius leads to the sluggish transport rate in the electrode and low specific capacity,which directly limits the energy density and power characteristics of SIBs.In SIBs,the electrode material is the key to influence its performance,so it is of great research value and significance to explore new high-performance electrode materials.Carbon-based materials and transition metal oxides are two types of candidates as anode materials for SIBs with high capacity,which are widely distributed in nature and cheap.In this work,we synthesize the amorphous hollow mesoporous carbon nanospheres(HMCNs)and hierarchical CuO nanocubes,whose mechanisms for sodium storage are investigated.(1)Hollow mesoporous carbon nanospheres(HMCNs-E and HMCNs-P)with different carbon shell thickness and pore structure were prepared from tetraethyl orthosilicate(TEOS)/tetrapropyl orthosilicate(TPOS),resorcinol(R)and formaldehyde(F)via the hydrolysis/condensation reaction and molecular self-assembly method in solution environment followed by carbonization and etching process.HMCNs-P possesses thicker carbon shell,abundant pore structure and higher specific surface area.However,HMCNs-E has thinner carbon shell and wider average carbon layer spacing.Both HMCNs-E and HMCNs-P show good sodium insertion/extraction properties,so they are expected to be the promising anode candidates for SIBs with high performance.Compared with HMCNs-E,HMCNs-P has higher specific surface area and porosity,so it shows a low interfacial charge transfer resistance and good Na⁺diffusion properties.However,HMCNs-E delivers a higher specific capacity for sodium storage and better rate capability during the charge and discharge test(the capacity retains at 200.5 m Ah g^-1under the current density of 100 m A g^-1after 100 cycles;the specific capacity retains at 152.8 m Ah g^-1after 1000 cycles at a high current density of 1 A g^-1),which can be attributed to the thin carbon shell that shorted the physical migration path of Na⁺and made full use of the active sites for sodium storage.(2)Hierarchical CuO nanocubes(side length is?1-2?m)were obtained through surface oxidation and nuclei removal by etching based on cuprous oxide micron-cubes,which were formed via self-assembly process using copper sulfate as the copper source and ascorbic acid as the reductant in the presence of trisodium citrate in alkaline solution.When used as SIBs anode,the initial reversible capacity of hierarchical CuO nanocubes could achieve 381.1 m Ah g^-1at current density of 100m Ah g^-1.Under the identical condition,the capacity value of micron-grade copper oxide is just 196.8 m Ah g^-1.This result benefits from the hierarchical microstructure and high specific surface area of CuO nanocubes,which supplies more active sites for Na⁺access.Whereas the capacity decay of CuO nanocubes is difficult to restrain effectively during the following cycles.In this paper,the molecular self-assembly method was adopted under wet chemical environment to synthesiz two sorts of HMCNs with different wall thickness and pore structure as well as a hierarchical CuO nanocubes.The intrinsic structure-function relationship between the microstructure and properties of sodium storage was comprehensively analyzed through the systematic characterizations of structure and the evaluation of electrochemical properties.The sodium storage mechanism of HMCNs and CuO nanocubes with hierarchical structure as active anode for SIBs was also explored,which provides theoretical references and materials support for the development of SIBs with high-performance in the future.