Design,Hydrothermal Synthesis And Electrochemical Performances Of Several Nanostructured Anode Materials For Lithium Ion Batteries

The development of clean and efficient new energy sources has become an urgent need as the demand for energy and environmental pollution intensifies.Lithium-ion batteries（LIBs）have been widely used due to environmental protection,light weight,high capacity,long life and other advantages.The present commercial graphite materials limited the improvement of electrochemical properties because of the lower theoretical capacity.The new carbon nanofibers have high conductivity,large specific surface area and other characteristics to show its potential application value.When evaluated as the anode in lithium ion batteries,carbon nanofibers can exhibit enhancing electrochemical performance.In addition,the low cost transition metal oxide has the advantages of high theoretical ratio and green pollution-free,which are also extensive attention by researchers.However,the large volume expansions and the rapid declining of reversible capacities and other factors restrict its application in energy storage material.In this paper,we design and synthesis carbon nanofibers and Cu_xCo_3-xO₄ hollow microspheres and uniform ReS₂ hierarchical nanospheres with new nanostructure via hydrothermal method,and their electrochemical properties and applications on LIBs are studied.The details are as follows:1.Research on the electrochemical properties of porous hollow carbon nanofibers and its application on energy-storage materialPorous hollow carbon nanofibers with tunable shell thicknesses from 2.5 to 13.5 nm have been synthesized via a hydrothermal approach by using multi-walled carbon nanotubes as the scaffolds and sucrose as carbon source.The thin,porous and non-graphitic carbon shells are revealed by X-ray diffraction,Raman spectra,high-resolution transmission electron microscopy,and nitrogen adsorption isotherms.It has been proved that the variations of shell microstructures such as the thickness and the pore structure have considerable impacts on the lithium storage performances when evaluated as the anode in coin-type lithium ion batteries.The porous hollow carbon nanofibers derived from 0.25 g of sucrose（shell thickness:⁵.0nm）delivers a specific capacity of 293.7 mA h g^-1 at a current density of 0.05 A g^-1 after 50cycles,which is higher than 215.8 mA h g^-1 of the pristine multi-walled carbon nanotubes.It means that the as-prepared porous hollow carbon nanofibers exhibit the enhanced reversible capacities,cycling stabilities and rater performances when evaluated as anode materials for lithium-ion batteries.2.Research on the electrochemical properties of Cu_xCo_3-xO₄ hollow microspheres and its application on energy-storage materialSpinel Cu_xCo_3-xO₄（x≤0.30）hollow microspheres have been readily prepared via a self-templated solvothermal reaction followed by a thermal annealing step.Scanning electron microscopy and transmission electron microscopy images show that the as-prepared hollow microspheres possess an average diameter of⁴50 nm and a compact,thin,polycrystalline shell with an average thickness of⁵0 nm.When used as anode materials for lithium-ion batteries,Cu_xCo_3-xO₄ hollow microspheres exhibit high lithium storage capacity,which is strongly dependent on the annealing temperature of the Cu_xCo_3-xO₄ intermediate.As a result,Cu_xCo_3-xO₄ hollow microspheres annealed at 400 ^oC deliver a reversible discharge specific capacity as high as 1187 mA h g^-1 at a current density of 100 mA g^-1 after 50cycles.Such superior lithium storage performance is derived from the particular microstructure of the shell,which is composed of highly close-connected fine nanoparticles,as well as the resultant better electronic conductivity.3.Research on the electrochemical properties of uniform ReS₂ hierarchical nanospheres and its application on energy-storage materialWe have developed a facile hydrothermal method to prepare the uniform ReS₂hierarchical nanospheres assembled by interlayer-expanded few-layer nanosheets,in which a lot of large pores are created by the curly ReS₂ nanosheets.The two-dimensional expanded interlayers help store more lithium ions and fasten lithium ion transports,and moreover the large void spaces in three-dimensional hierarchical nanospheres benefit for buffering the volume expansion and preserving the electrode integrity during the lithiation/delithiation process.When evaluated as anode materials for lithium-ion batteries,the unique ReS₂nanospheres deliver a remarkably enhanced reversible capacity of 1011 mAh g^-1 with an over100%capacity retention at a current density of 100 mA g^-1 after 100 cycles,in comparison with the solid ReS₂ microparticles(458 mA h g^-1 with a capacity retention of merely 75%at the same condition).The relatively high reversible capacity suggests the ReS₂ hierarchical nanospheres.