Preparation And Lithium Storage Behavior Of Composite Electrodes For Lithium Titanate-Based Lithium-Ion Batteries

In the ever-changing society,graphite,the traditional anode material for lithium-ion batteries,runs counter to the expectations of today’s energy industry for lithium-ion batteries due to its own low energy density,slow charging speed and poor safety,making it difficult to meet the requirements of new lithium-ion batteries.In order to solve the dilemma faced by lithium-ion batteries,various new materials have received extensive attention.Lithium titanate(Li₄Ti₅O₁₂),as an inorganic lithium-containing compound,has the advantage that the theoretical volume expansion of Li₄Ti₅O₁₂ is less than 0.2%after embedding lithium and maintains a stable structure during cycling,and its battery shows excellent cycling performance and safety performance,which is considered a battery cathode material with great potential for development,however,the material itself has some defects,such as theoretical However,the material itself has some defects,such as extremely low energy density,poor electrical conductivity and high price,which limit its development in the field of negative electrode.In this paper,we firstly analyze the improvement of Li₄Ti₅O₁₂ material by controlling the nanostructure and morphology of the material.On this basis,the high conductivity carbon materials（RGO,CNTs）are compounded to overcome the deficiencies of single materials as anode materials for Li-ion batteries,and finally,doping ions are introduced on the basis of the composite materials to realize the composite modification of the materials.The main research contents of this paper include:（1）In this paper,different lithium sources（lithium hydroxide and lithium acetate）,n-butyl titanate as the titanium source and CTAB as the surfactant were used to synthesize as lithium titanate samples with special graded structure by hydrothermal and sol-gel methods,starting from the nanostructure design of the materials.It was found that the synthesized lithium titanate samples were characterized as nanosheet-assembled microspheres and particle-assembled microspheres with graded structures,in which the hydrothermal reaction time and the degree of hydrolysis of n-butyl titanate in the preparation process played a key role in the morphology.The electrochemical performance of the synthesized lithium titanate with graded structure was tested as anode material for lithium-ion batteries,and the discharge specific capacity was increased by43.21%and 51.25%,respectively,compared with that of ordinary lithium titanate flakes at high current density of 1500 m A g^-1.After a long cycle of 200 cycles at a current density of 100 m A g^-1,the capacity retention rates of nanosheet-assembled microspheres and particle-assembled microspheres are 90.21%and 92.87%,showing excellent cycling performance,which is about 10%higher than that of ordinary lithium titanate flakes（80.27%）and 18%and 35.23%higher in initial discharge specific capacity,respectively.This indicates that Li₄Ti₅O₁₂ materials with graded structure and special morphology of nanosheet-assembled microspheres and particle-assembled microspheres can effectively improve the battery charge/discharge capacity,as well as the multiplicative performance and cycling performance of the battery.（2）In this paper,from the direction of material composite,Li₄Ti₅O₁₂/C composites were prepared by hydrothermal and calcination methods using n-butyl titanate,lithium hydroxide and CTAB as raw materials and adding high conductivity carbon nanotubes and graphene oxide for compounding,respectively.In this paper,the effects of Li₄Ti₅O₁₂compounded with different carbon materials and at different calcination temperatures on the material properties were investigated,which showed that the Li₄Ti₅O₁₂ material compounded with carbon nanotubes and graphene oxide at 650°C produced materials with excellent electrochemical properties,in which the lithium ion diffusion coefficients of both LTO/CNTs（650）and LTO/RGO（650）were The capacity retention after 200cycles is 95.22%and 90.03%,which is 25.27%and 20.08%higher than that of the single material,respectively.multiplicative performance.This indicates that the composite high conductive carbon material and controlled calcination temperature can effectively improve the comprehensive battery performance of Li₄Ti₅O₁₂.（3）In this paper,by studying the ionic doping and material composite synergy starting from graphene oxide as a substrate,n-butyl titanate and lithium hydroxide as raw materials,yttrium nitrate as dopant and CTAB as surfactant.The reaction precursors were synthesized by hydrothermal method,and the yttrium-doped lithium titanate/graphene composites were synthesized at high temperature under nitrogen protection.The material composition and structure as well as electrochemical properties were investigated by means of XRD,Raman,SEM,EDS,and electrochemical performance tests.The initial charge/discharge capacity of LTO（Y）/RGO nanocomposite was 145 m Ah g^-1 at a current density of 100 m A g^-1,which was 17%higher than that of the single material.This indicates that the LTO（Y）/RGO material can reduce the polarization of Li₄Ti₅O₁₂ battery during charge/discharge cycle by the synergistic effect of Y element doping and graphene composite.thus improving the cycling performance of the material.