Research On Structural Charge And Decay Process The Anode Material FeTiO₃ For Lithium Ion Batteries

Lithium-ion battery is a device that converts chemical energy into electric energy and can store the energy.It has the advantages of safety,environmental protection and high electrochemical performance.Conventional Li-ion batteries consist of a positive electrode,a negative electrode and an electrolyte.As a very important part of Li-ion battery,the negative electrode plays an important role in Li-ion battery.Transition metal oxides（TMOs）have high energy density,wide electrochemical window,low electrode potential and good stability,so they are considered to be very promising anode materials for Li-ion batteries.However,due to volume expansion,REDOX reaction of materials and SEI film and other factors,the battery capacity rapidly decay,and even failure.At present,researchers usually use cyclic voltammetry and AC impedance methods to evaluate the negative electrode performance of Li-ion batteries,but there is little research on the underlying cause of performance attenuation.This paper takes the new transition metal oxide FeTiO₃ anode material as the research object,systematically explores its structural evolution law in the cycle process,and deeply analyzes the causes of its capacity attenuation and electrode aging,so as to provide reference for the subsequent research on related anode materials.Specific research contents are as follows:Taking FeTiO₃ as the research object,the structure evolution of FeTiO₃ anode material during the cycle was investigated directly or indirectly by using in-situ TEM and selected electron diffraction.The experimental results show that FeTiO₃ changes into Li FeTiO₄,Fe O plus Li₂Ti O₃ and Fe O plus Ti₃O at different potentials during charging and discharging.The surface structure was measured by non-situ photoelectron spectroscopy at different potentials.The electrochemical reaction process of FeTiO₃ anode in Li-ion batteries was deduced by combining the results of non-in-situ photoelectron spectroscopy,transmission electron microscopy and selected electron diffraction,which provided a theoretical basis for the development of related new transition metal oxide anode materials.Based on the above research basis,the structural evolution law of FeTiO₃ anode material in different cycle processes is further explored,and the relationship between performance and negative electrode structure in different cycle processes is studied.Selective electron diffraction and high resolution transmission electron microscopy were used to characterize the structural changes of FeTiO₃ during the cycle.It was found that FeTiO₃ was formed by alternating connections of[Fe O₆]and[Ti O₆].The study of the evolution process of FeTiO₃ negative electrode is also helpful to explore the evolution law of Fe and Ti,two typical elements in the oxide negative electrode.The results show that FeTiO₃ is gradually decomposed into Ti O₂ and Fe₃O₄ due to the continuous spillover of Fe element in the recycling process of the anode material.Meanwhile,SEI film grows gradually.The growth process is from surface to interior and from uneven to uniform.When the SEI film is uniformly coated on the surface of the active material,the electrode surface will be pulverized and the negative electrode will fail.According to the negative failure process of FeTiO₃ transition metal oxides,it is of great importance to explore the negative failure mechanism of transition metal oxides related to iron and titanium.