Study On The Electrochemical Properties Of Fe₃O₄/TiO₂@melamine Resin With The Core-shell Structure As Anode Material

With the rapid development of science and technology,the experts in the field of energy believe that the research direction of lithium ion batteries in the future is the development of the negative electrode materials with high capacity,long service life and excellent safety performance.Among the materials studied,Fe₃O₄ and TiO₂ are always the new generation of lithium-ion battery anode materials,which the researchers focus on.The obvious advantages of Fe₃O₄ lie in the high theory specific capacity(926 mAh g^-1),low price and good environment,and the remarkable potential of TiO₂ is the small volume change in the process of intercalation and removal of lithium and high lithium insertion potential.However,on the other hand,the shortcomings the two materials limit their application to some extent as the anode materials for lithium ion batteries,which are the big volume expansion of Fe₃O₄ in the process of intercalation and removal of lithium and the low capacity of TiO₂(168mAh g^-1).In this paper,melamine formaldehyde is the precursor of the nitrogen doped carbon coating.Therefore,we designed and successfully prepared the yolk-shell structured Fe₃O₄@Void@C-N nanocomposite particles and porous hollow TiO₂@NC nanocomposite particles.The electrochemical properties of the anode materials of lithium ion batteries have been significantly improved by the modification of excellent conductive materials,and the specific research contents of this research topic are as follows:?1?The hydrothermal method was applied to synthesize the core of the yolk-shell structure,Fe₃O₄ particle,and the synthesized Fe₃O₄ particles have the characteristics of uniform particle size distribution.SiO₂ coating layer was synthesized by the St?ber method,and the melamine formaldehyde was synthesized under the catalysis of acetic acid.Finally,the yolk-shell structured Fe₃O₄@Void@C-N nanocomposite particles were formed by calcination and etching in turn.The theoretical research shows that the presence of mesoporous nitrogen doped carbon coating can avoid the aggregation of Fe₃O₄ nanoparticles,and buffer the volume change of Fe₃O₄ during the charge discharge cycle,thus improving the electrochemical properties of the yolk-shell structured Fe₃O₄@Void@C-N nanocomposite particles.The results of performance testing manifest that the yolk-shell structured Fe₃O₄@Void@C-N nanocomposite particles have good charge and discharge performance and cycle performance,the discharge capacity of nanocomposite particles was 1530 mAh g^-1 under the current density of 500 mA g^-1after 300 laps,which were approximately 1.5 and 6 times higher than Fe₃O₄@C-N nanocomposite particles and pure Fe₃O₄ particles,respectively,and the discharge capacity of nanocomposite particles was 651 m Ah g^-1under the current density of 2000 mA g^-1after 500 cycles.?2?SiO₂ and TiO₂ coatings were synthesized by the St?ber method in turn,and the melamine formaldehyde was synthesized under the catalysis of acetic acid.Finally,the porous hollow TiO₂@NC nanocomposite particles were formed by calcination and etching in turn.Transmission electron microscopy showed that the thickness of TiO₂and nitrogen doped carbon layer of the porous hollow TiO₂@NC nanocomposite particles was¹0 nm,respectively.The result of nitrogen adsorption-desorption isotherms shows that the porous hollow TiO₂@NC nanocomposite particles have a larger surface area(59.29 m² g^-1)and mesoporous?².8 nm?,and the rate of lithium ion diffusion and thr contact of electrolyte and anode were improved due to the large surface area and mesoporous.Therefore,the electrochemical performance of nanocomposite particles was significantly improved compared with pure TiO₂.The discharge specific capacity of the porous hollow TiO₂@NC nanocomposite particles is about 251 mAh g^-1 under the current density of 100 mA g^-1 current density after 200cycles,and the capacity retention ratio is about 96.91%compared with the second cycle.In addition,the porous hollow TiO₂@NC nanocomposite particles have a stable long cycle performance,and the specific discharge capacities are 238 mAh g^-1and 170mAh g^-1 under the current density of 500 mA g^-1 and 2000 mA g^-1,respectively.The electrochemical impedance spectroscopy results are further demonstrated that the presence of the hollow structure and the mesoporous nitrogen doped carbon coating enhances the conductivity of the nanocomposite particles.