The Lithium Storage Performance Of Transition Metal Oxide And Porous Carbon Nanocomposites Anode Material

At present,rechargeable lithium-ion batteries have been proven to be one of the mature battery systems,and have achieved great success in various consumer electronic products(mobile power,mobile phones,computers,electric vehicles,etc.).However,the graphite capacity of commercial lithium-ion battery anode materials is relatively low.With the development of the electronic society,people's demand for energy storage is increasing.Therefore,the problem of energy storage has become an urgent problem for scientists.The key to improving the electrochemical performance of batteries is to develop advanced electrode materials.The characteristics of transition metal oxides with high energy density have attracted wide attention from researchers.However,it is limited by shortcomings such as easy volume expansion during charging and discharging,resulting in electrode damage and poor conductivity,which also restricts its further practical application.The problem of volume deformation can be effectively solved by designing nano-scale transition metal oxide particles or adjusting their morphology and structure to be combined with carbon materials.In addition,the covalent organic frame material is a new type of environmentally friendly,structure-adjustable electrode material for rechargeable batteries,which has received extensive attention in recent years.For this reason,this thesis mainly focuses on the preparation of transition metal oxide/carbon nanocomposite materials and their application in lithium-ion battery anodes.The specific research content mainly includes the following three tasks:1.Dictyophoraindusiatawas used as raw materials,through simple hydrothermal reaction and unique triethylamine(TEA)combustion method,to simply and effectively prepare dandelion-like Co O/Co₃O₄/dictyophoraindusiata-derived carbon(DIC)materials.The resulting Co O/Co₃O₄/DIC composite material has a three-dimensional conductive network and a porous structure,which facilitates the electron transport,and also enhances the contact area with the electrolyte,effectively alleviating the damage from volume expansion during discharge/charge process.During the TEA combustion process,a large amount of thermal energy and active groups are released,and the DIC is crosslinked successfully to form a stable nitrogen-doped Co O/Co₃O_4/DIC composite.When used as a negative electrode material for lithium-ion batteries,it can still provide a high capacity of 545 m Ah g^-1 at a current density of 1000 m A g^-1after 250 cycles.The readily available and renewable biomass material assisted strategy is of great significance for achieving efficient electrochemical energy storage.2.N-doped honeycomb-like carbon networks(N-HCN)loaded with ultra-fine Fe₂O₃ nanoparticles(Fe₂O₃/N-HCN)are proposed as anode materials for lithium-ion batteries(LIBs).The Fe₂O₃/N-HCN nanocomposites are prepared by freeze-drying of glucose-Fe(NO₃)₃ solution,following by grinding it with urea,and finally annealing treatment.The N-HCN with dozen micrometer-sized macropores are composed of ultra-thin carbon nanosheets with a thickness of about 33 nm.A large number of 2-7nm-sized ultra-fine Fe₂O₃ nanoparticles with an average size of 4.4 nm are uniformly arrayed on the wall of N-HCN.The Fe₂O₃/N-HCNnanocomposites exhibit good performances as anode materials for LIBs.After 500 cycles under a large current density of 5 A g^-1,the Fe₂O₃/N-HCNnanocomposites still show a reversible capacity of 408 m Ah g^-1.The good performance can be ascribed to the uniformly dispersed ultra-fine Fe₂O₃ nanoparticles and unique honeycomb-like structure of N-HCN which provides a continuous conductive network to greatly promote the rapid transfer of ions and electrons,and effectively alleviate the volume fluctuation effect of Fe₂O₃during charging and discharging.More importantly,the cheap and environmentally friendly glucose as raw materials provide possibility for green energy applications.3.A new type of candied fruit-like Co₃O₄@CNT composite material was obtained by incorporating cobalt acetate tetrahydrate into COF_TAPT-DHNDA and using a two-step calcination method through reasonable design.The material has a hollow nano-Co₃O₄sphere structure wrapped by carbon nanotubes.This strategy can not only improve electronic conductivity,but also give Co₃O₄nanoparticles more room for expansion.At the same time,nitrogen-doped carbon nanotubes provide more active sites,further improving the electrochemical performance of lithium-ion batteries.Therefore,the Co₃O₄@CNT composite material has good electrochemical performance as the negative electrode material of lithium-ion batteries.After 100cycles of 0.2 A g^-1,the reversible specific capacity reaches 808.0 m Ah g^-1,and the high current is 2 A g^-1.The reversible specific capacity can still reach 540.0 m Ah g^-1after 200 cycles at the density.The target composite material prepared by the combination of COF-derived nitrogen-doped carbon nanotubes(CNT)and hollow Co₃O₄ metal oxides obtained good electrochemical performance,novel structure,and provided a new way for the design of lithium-ion batteries way.