Synthesis Of MOFs-derived Carbon-based Composites And Their Lithium Batteries Anode Performance

Lithium-ion batterry plays a vital role in the market;it has become the main supplier for power industry due to its high energy density,power density,high efficiency,environmental protection,long cycle life,etc.However,with the development of electronic products and the worldwide popularity of new energy vehicle,especially electric vehicle,the market has set higher requirements for the development of lithium-ion batterry to meet the market demand.As one of the most important factors affecting battery performance,anode electrode materials have become the current research hotspot for researchers.At present,graphite as a siganificant material for the anode of lithium ion battery is obviously can not meet the demand of the growing market.Metal oxide has become a potential substitute for graphite anode due to its ultra-high theoretical capacity.Nevertheless,during the cycle in the process of charging and discharging,metal oxide anode materials not only have the problem of low electrical conductivity,but also are prone to volume expansion during cycling,which seriously affects the electrochemical performance and cycle life of lithium-ion batteries.Exploring how to solve the problem of low conductivity of metal oxide materials and volume expansion during cycling is still the key to preparing high-performance lithium-ion battery materials.In this paper,by preparing MOFs material derivatives with high specific surface area can achieve the purpose of compositing metal oxides and nano-carbon materials andsystematically study the influence of material composition and structure on the electrochemical performance of lithium-ion batteries,which aims to achieve the preparation of metal oxide anode materials with longer cycle life and higher electrochemical performance.The main research contents are as follows:（1）Using the ultra-high specific surface area ZIF-8 as the carrier,ZIF-8@CuO material was prepared by one-step method at room temperature,and then ZnO-CuOx@C nanomaterial with porous carbon-coated bimetal anode was prepared by post-annealing treatment.The generated bimetallic nanoparticles were uniformly loaded on the surface of the carbon nanomaterials,exhibiting good dispersibility,and the size of the particles was uniform.The synergistic effect of bimetal and the coating of carbon materials can significantly improve the lithium storage capacity and electrical conductivity of electrode materials.The electrochemical performance of the ZnO-CuOx@C nanocomposite reached the highest when the addition amount of CuO is 0.1 mmol,which showed that ZnO-CuOx@C had a good capacity of 1061.2 m Ah g^-1after 500 cycles at a current density of 100 mAg^-1and maintained a good capacity of 469.6 m Ah g^-1after 1000 cycles at the current density of 1 A g^-1.（2）The SBA-15 was used as template and by one-step process to prepare the nano-confined material Fe₂O₃@OMC material.Through characterization and analysis,it can be seen that the MOFs derivative Fe₂O₃was successfully confined in the mesoporous carbon material,and the morphology and crystal structure of the confined material remained unchanged.Fe₂O₃@OMC had high specific surface area of 307.94 m²g^-1,and the pore size was concentrated at 4 nm.The large specific surface area not only provides more places for electrochemical reactions,but also provides more sites for the deintercalation of lithium ions.The capacity can bemaintained at 1176.6 m Ah g^-1after 400cycles at the current density of 100 mAg^-1,and even the capacity can reach 508 m Ah g^-1after 1100 cycles at the current density of 1 A g^-1,showing ultra-long cycle stability.More importently,this work also provides a new idea for the simple confinement synthesis of anode materials.（3）The bimetal hollow MOFs Ti@ZIF-67 was prepared by hydrothermal method,and then TiO₂/Co₃O₄@C composite material was prepared by baking at different temperatures.The composite material showed the three-dimensional nanocage structure with the size of 200 nm.This stable structure made the metal oxide particles uniformly and stably confined in the nanomaterial.After roasted at 450℃,the composite had better morphological structure and electrochemical performance.Under the synergistic effect of the bimetal,TiO₂/Co₃O₄@C exhibited extremely excellent electrochemical performance.Not only it can maintain the capacity of 600 m Ah g^-1after 500 cycles at the low current density of 100 mAg^-1,but also it can maintain the capacity of 600 m Ah g^-1after multiple cycles at different densities of 200 mAg^-1,1 A g^-1,2 A g^-1,and even 5 A g^-1.Those tests all showed that the three-dimensional nano-cage structure can effectively solve the problem of volume expansion of metal oxide materials in electrochemical reactions,which is benificial for excellent long-cycle performance.At the same time,the synergistic effect of bimetal and the doping of heteroatoms can improve the lithium storage capacity and rate performance of electrode materials.（4）Using ZIF-67 as the carrier,the MOFs derivative Mn@ZIF-67 material was prepared by a one-step method,and then calcined at different temperatures to obtain MnCo@C nanocomposites.The study found that Mn₂Co₂C@C nanocomposites with high specific surface area can be obtained by annealing at 800℃when manganese acetate as the manganese source.It exhibited a three-dimensional cross-linked structure and the nano particles are uniformly dispersed,and the electrochemical performance shows the best.Its capacity can maintain 600 m Ah g^-1after 500 cycles at the current densities of 2 A g^-1,while the capacity can reach 1177.1 m Ah g^-1at the low current density of 100 mAg^-1.In the reaction process,the appropriate pore size and the synergistic effect of the bimetal can improve the electrochemical reaction activity and the doping of heteroatoms can add a large number of active sites for the electrode reaction to ensure excellent rate performance,which corresponds to the result that the material has a higher contribution rate of pseudocapacitance in the kinetic calculation.