Modification And Electrochemical Performance Of Insertion-Type Anode Materials In Li-ion Batteries

The widespread adoption of electric vehicles has been limited by factors such as driving range and charging time.The fast charging performance of the battery is a key factor in improving the charging speed of electric vehicles,and the anode material is one of the key factors in determining the charging speed of the battery.Therefore,the development of anode materials with low cost,fast charging speed and long cycle life is an urgent need for electric vehicles.The fast charging performance is mainly affected by the transport rate of materials,including electrons and ions,and under a large rate,the insufficient transport capacity will be further amplified,which seriously affects the rate performance.It is difficult for anode materials to take into account the ionic/electronic conductivity properties,and its fast charging capability is greatly restricted.Commonly used anode materials for fast charging,such as lithium titanate,titanium niobium oxide,etc.,due to their unique structure,have fast ion transfer rate,but insufficient electron conductivity,leading to difficult to take advantage of fast ion transfer under a high rate,and the fast charging ability is rapidly attenuated.In view of the above shortcomings,this paper focuses on the modification strategies of traditional fast charging materials such as lithium titanate and titanium niobium oxide,and optimizes the design of the materials by in-situ derivatization and construction of composite materials,structural control and doping synergy.The effects of electronic conduction（including interface conduction and bulk conduction）and electrode structure on the fast charging capability provide a certain basis for the design of high-rate electrodes.The main research contents include the following:（1）In situ-growth Ti₃C₂Tx MXene/Li₄TisO₁₂（M-LTO）nanocomposites were prepared by controlled natural oxidation and hydrothermal methods using sheet-like Ti₃C₂Tx MXene as the titanium source and conductive framework.Monodisperse Li₄Ti₅O₁₂ nanoparticles grow uniformly on the surface of Ti₃C₂Tx MXene,and the large specific surface area of Ti₃C₂Tx MXene provides more active sites and reduces the diffusion paths of lithium ions,thereby improving the utilization of the material.The M-LTO-8 anode material exhibits a reversible capacity of 137 mAh g-1 at 10C（1C=175 mA g-1）and over 125 mAh g-1 at a high rate of 50C.The capacity retention rate of 1000 cycles at 10C rate is 87.5%,which is much higher than that of single-component Li₄Ti₅O₁₂,Ti₃C₂T,MXene and the mechanical mixture of the two.The study showed that the in-situ grown M-LTO nanocomposites had a certain crystal orientation between Li₄Ti₅O₁₂ and Ti₃C₂Tx MXene,namely Li₄Ti₅O₁₂[110]//Ti₃C₂Tx MXene[001],indicating the existence of an in-situ interface.The in-situ interface exhibits low electron polarization resistance,which is very effective in promoting electron transfer,revealing that enhancing the electron transport ability between electrode materials and current collectors can effectively improve the electrode rate performance.（2）The structure and conductivity of TiNb₂O₇ electrode material were regulated by adding surfactant and La3+doping.The surfactant polyvinylpyrrolidone（PVP）can effectively inhibit the agglomeration of TiNb₂O₇ nanoparticles during wet chemical synthesis,forming a mesoporous structure,significantly increasing the contact area between the electrode and the electrolyte,and shortening the diffusion of lithium ions in the active material.At the same time,the pyrolysis of PVP during the calcination process will partially reduce the surface O2-,leaving oxygen vacancies.In addition,La3+doping can induce TiNb₂O₇ to generate oxygen vacancies through charge conservation.Theoretical calculations show that the existence of oxygen vacancies promotes the shift of the Fermi level to the higher energy level,and the impurity level is formed below the Fermi level after doping,indicating that La3+ doping and oxygen vacancies can effectively improve the electronic conductivity,which is consistent with the The experimental results are consistent.The results show that La-M-TNO（0.03）electrode is as high as 213 mAh g-1 at 30C,and not only that,the rate performance is gradually improved by the enhancement of porous structure and intrinsic conductivity,the capacity of TNO,M-TNO and La-M-TNO（0.03）is gradually improved.Capacity retention（@30C/@1C）increases from 33%to 53%,and 74%,respectively.Therefore,the synergistic effect of La3+doping and mesoporous structure leads to the double enhancement of electronic conductivity and ionic diffusion coefficient.Finally,the GITT method was used to prove that the mesoporous structure accelerated the Li+diffusion rate by shortening Li+diffusion path,and revealed the reason why increasing the La3+ doping concentration actually reduced the electrochemical performance.