Preparation Of T-Nb₂O₅ Composites And Their Application In Lithium-ion Battery Anodes

With the development of new energy industry,lithium-ion battery with high energy density,good cycle life,safety and environmental protection are widely used in wearable electronic devices and electric vehicles.Graphite electrode has been widely used because of the advantages of its rich resources,stable structure,environmental friendliness and so on,but it has a slow reaction kinetics of lithium ion and low theoretical specific capacity,which can not meet the market demand.As a lithium ion anode material,Nb₂O₅ has been widely studied for its advantages of stable structure,fast Li-ion diffusion rate and safe in cycling process.However,Nb₂O₅ with intercalation mechanism has low theoretical specific capacity and poor electrical conductivity,which limits its commercial application.In this paper,by taking Nb₂O₅as the main body,the carbon composite structure is designed and the anode material with conversion mechanism is introduced.It is committed to studying The Nb-based anode material with high theoretical specific capacity,high conductivity and good structure stability.The morphology,elemental composition and mass ratio of the prepared materials were analyzed by SEM,TEM,XRD,XPS and TG,and the best lithium ion anode materials of Nb₂O₅ were confirmed by electrochemical testing.The specific work content and results are as follows:1.NbO_x/OAc precursor with spherical structure was prepared by solvothermal method,adding dopamine as carbon source for acylation and self-polymerization reaction,and calcination at 850?to obtain T-Nb₂O₅/C composite with double spherical structure.The effect of carbon content on the electrochemical performance of the composites was investigated.The composites with different morphologies and sizes were obtained by controlling the time and content of dopamine self-polymerization.The electrochemical test results show that T-Nb₂O₅/C composite electrode exhibits excellent electrochemical performance,which proves that the combination of carbon improves the conductivity of the composite material,provides abundant active sites,and improves the defect of Nb₂O₅ with low theoretical capacity.Meanwhile,the T-Nb₂O₅/C-0.2 composite structure with optimum carbon content has the best electrochemical performance.The electrode delivers the reversible specific capacity of 350 m Ah g^-1 at current density of 0.1 A g^-1 and 102 m Ah g^-1at current density of 2 A g^-1,which shows high rate performance.In addition,T-Nb₂O₅/C-0.2 shows excellent cyclic stability with the capacity retention rate of 73.3%after 1000 cycles at 1 A g^-1.2.In order to further optimize the electrochemical performance of the previous research,Mo S₂ with high theoretical specific capacity was introduced to increase the lithium ion active site and improve the capacity of the composite material.NbO_x@Mo S₂ precursor was prepared by one-step solvothermal synthesis,and then dopamine carbon source was introduced.Massive T-Nb₂O₅@Mo S₂@C with three-phase complex was obtained by calcination of precursors at high temperature.The effects of different Nb/Mo molar ratios on the electrochemical performance of the composites were investigated.The results show that the introduction of Mo S₂ not only improves the specific capacity of the composites,but also accelerates the diffusion rate of lithium ions.It was found that T-Nb₂O₅@Mo S₂@C-1-1showed the best electrochemical performance,because the proportion of Nb₂O₅,Mo S₂ and C in the composite reached the best synergistic effect.The high reversible specific capacity of the electrode is 518 m Ah g^-1 at current density of 0.1 A g^-1.Most notably,the T-Nb₂O₅@Mo S₂@C-1-1 composite shows excellent cyclic stability with capacity retention rate of 94.6%after 600 cycles at current density of 0.5 A g^-1.Moreover,the capacity still remain187 m Ah g^-1 with the retention rate of 84.6%after 1000 cycles at current density of 2 A g^-1.3.T-Nb₂O₅@NbS₂ composites were prepared by oil phase synthesis process with carbon disulfide as sulfur source and further synthesizing carbon by subsequent carbonization.As a result,the introduction of NbS₂ with a conversion mechanism can effectively improve the low theoretical specific capacity of Nb₂O₅ with an intercalation mechanism in the field of lithium-ion anodes,and the in situ synthesized carbon overcomes poor conductivity of pure Nb₂O₅.The results show that the reversible capacity of T-Nb₂O₅ electrode is 173 m Ah g^-1 at the current density of 0.1 A g^-1,while the reversible capacity of T-Nb₂O₅@NbS₂@C electrode material is increased to 636 m Ah g^-1.Additionally,it also displayed a better cycle performance at current density of 0.5 A g^-1 after 400 cycles.Compared with the T-Nb₂O₅electrode,its capacitance retention has increased by 21%.Furthermore,the T-Nb₂O₅@NbS₂@C electrode maintained a capacity of 102 m Ah g^-1 at a current density of 2 A g^-1 after 500 cycles with a high CE of approximately 100%.