Study On The Development And Application Of High Performance Transiton Metal(Carbonate)/Carbon Composite Anode Materials For Lithium Ions Batteries

In this century,low-carbon and electric drive have become the main theme of the times.The market share of electric vehicles and the electric power generated by new energy power station are increasing day by day.The demand for power-type and large-scale energy storage lithium-ion batteries is also continuously increasing.Meanwhile,higher requirements have also been placed on battery life,power and energy density of lithium ion batteries.As a key component of lithium-ion batteries,anode materials are one of the key factors determining their performance.Based on this situation,this dissertation is devoted to solving the key scientific problems such as difficulty in ion and electron transport within high tap density micron sized negative particles and low tap density of nanosized negative electrode materials,as well as the poor conductivity,the poor cycle stability,etc.Making full use of the high specific surface area and excellent conductivity of one-dimensional carbon nanotubes and two-dimensional graphene,carbon nanotubes"neural network"contained high-capacity binary Sb_xMn_1-xCO₃ microspheres and high-rate,long-cycle graphene coated Bi@C-TiO_x anode material with long-short-range multi-level conductive network are successfully prepared by one-step or multi-step methods.The inside and outside carbon,CNTs and graphene network could provide a channel for rapid transportation of lithium ions and electrons.The specific research content is as follows:1?To boost the electrochemical performance of MnCO₃?MC?microspheres,it was prepared using a solvothermal method in-situ enthalpy doping Sb,A 3D conductive network of carbon nanotubes?CNT?was also successfully built from the inside to the surface of the microspheres to promote electronic and ionic transportation.As observed,the doping of an appropriate amount of Sb helps to improve the overall performance of the material.the microspheres of Sb_1/3Mn_2/3CO₃ were larger and had a more uniform distribution compared with pure MnCO₃,Sb_1/2Mn_1/2CO₃ and Sb_2/3Mn_1/3CO₃.Profting from the introduction of neural-like CNTs networks,the electrochemical performance and the utility of the Sb_1/3Mn_2/3CO₃ microspheres?approximately 3.5-7?m in diameter?were remarkably improved.The obtained CNTs@Sb_1/3Mn_2/3CO₃ composite anode delivered 1066 and 572mAh g^-1 at current densities of 500 and 5000 mA g^-1 after 200 cycles,respectively,which were much higher than the 737 and 297 mAh g^-1 of bare Sb_1/3Mn_2/3CO₃.2?Bismuth?Bi?,a uniquely stable pnictogen element,is deemed a promising anode material for lithium-ion batteries owing to its high volumetric capacity,moderate operating voltage and environmental friendliness.The application of Bi as anode is hindered by its low conductivity and large volume change during cycling.Herein,we introduce an advanced surface engineering strategy to construct Bi@C-TiO_x microspheres encapsulated by ultra-large graphene interfacial layer.Ultrafine Bi nanoparticles are confined and uniformly dispersed inside the C-TiO_x matrix,which is the pyrolysis derivative of the newly developed Bi-Ti-EG bimetal organic frameworks,with the aid of a selective graphene interfacial barrier.A three-dimensional?3D?long-range conductive network is constructed by the ultra-large graphene and the carbonized derivative of Bi-Ti-EG.Additionally,the 3D carbon network and the in-situ formed TiO_x coupled with a porous structure act as soft buffer and hard suppressor to alleviate the huge volume change of Bi during cycling,and they also are the important electrochemically active components.Thanks to the synergistic effects intrigued by the aforementioned interfacial engineering strategy,the newly developed ultra-large graphene encapsulated Bi@C-TiO_x microspheres exhibit an exceptional superpower and outstanding cycle stability(namely,333.3,275 and 225 mAh g^-11 at 1,5 and 10 A g^-1,respectively,and 5000 cycles at a current density of 10 A g^-1,the charge capacity remains at119.5 mAh g^-1.This study underpins that designing and constructing a rapid migration channel of ions and electrons and introducing a multi-layer stress buffering mechanism is an effective approach to significantly enhance the power capability,capacity and cyclic stability of the high bulk density negative electrode and the metal negative electrode.