Study On The Method Of Prediction Of Organic Cathode Electrode Materials

With the rapid development of new electronic products,the traditional lithium-ion battery cathode materials due to high cost,non-renewable,difficult to recover and pollute the environment and other shortcomings have been unable to meet the needs of the market.Therefore,the study of energy-efficient,resource-rich and environmentally friendly energy storage materials has become a necessary condition for the sustainable development of human society.Organic compounds as the electrode materials has been widely concerned,mainly because of the organic material is light weight,flexibility is good,rich in natural resources.Organic compounds can be used to design green electrochemical storage devices.At present,in many reported organic electrode materials,the structure of diverse,molecular level control and theoretical specific capacity of organic conjugated carbonyl compounds have been widely used in lithium/sodium ion batteries.In recent years,density functional theory has gradually become a very effective calculation method.However,the existing density functional theory method is still not accurate for the correction of intermolecular long-range dispersion,and the treatment of sodium ion electrode materials is not clear.Therefore,the research point of this paper lies in the establishment of an accurate method of high-throughput screening for organic electrode materials to find out the best organic electrode materials,for the experimental guidance.This paper consists of five chapters and the specific contents are as follows:In chapter 1,the first chapter,the development history,working principle and prospect for lithium/sodium ion battery are reviewed.Further introduction to the lithium/sodium ion battery components,including the cathode materials in this paper and discuss the advantages and disadvantages of the existing industrial inorganic cathode materials.This paper introduces the development history of organic cathode materials,especially organic compounds with conjugated structures.Finally,the main work and innovation of this paper are introduced.In chapter 2,we summarizes up the development of the first principle calculation and the density functional theory model,and its application to correction of the dispersion force and the hybrid functionals.Then the hybrid functional theory of battery electrode is introduced.Finally,the paper describes the software package used in the calculation process,and the instruments used in the experiment process.In chapter 3,we establish a kind of accurate high-throughput screening theoretical scheme that could find out possible candidates of electrode materials.hybrid functionals and vdW correction methods are applied to investigate six reported organic electrode materials for Li-ion batteries.Through the optimization of the structure of the materials,the geometrical parameters of the various calculations are compared and the experimental values are taken as the standard.The comparison between the calculated lithium potential and the experimental data shows that the hybrid functional combined with the D2 dispersion corrected method,i.e.,HSE06-D2（Heyd,Scuseria,and Ernzerhof,dispersion-corrected）,is able to predict the potential for the organic material precisely with an average error of approximately 5%.This method occupies much hardware resources and being very time consuming,but it could be applied as the final ultra-fine step in the high-throughput screening program.In chapter 4,compared to lithium-ion battery electrode materials,sodium-ion battery electrode materials are more abundant and more cost effective.Therefore,a fast and accurate theoretical method for finding possible candidates for organic electrode materials for Na-ion batteries is urgently needed.The organic electrode materials of five kinds of sodium ion batteries were studied by using the D2dispersion-corrected hybrid functional method（HSE06-D2）.The results show that this functional method can precisely calculate the potential for organic materials with a small average error of approximately 3.68%,indicating that the theoretical calculation method of lithium ion battery electrode materials for sodium ion battery electrode material prediction is feasible.The band gap values are approximately lower than 2.5 eV,which proves that the materials have good conductivity and are expected to be candidates for organic electrode materials for sodium-ion batteries.In chapter 5,the dispersion-corrected hybrid functional theory（HSE06-D2）method is applied to study an organic compound,thioindigo(SINDIG,C₁₆H₈S₂O₂),which is a novel cathode material of sodium ion battery based on the theoretical calculation results.The two charge/discharge platforms’potentials and the intermediate state in the charge/discharge process are successfully explored for the theoretical method,which are verified by the CV（cyclic voltammetry）test and ex-situ XRD（X-ray diffraction）measure.The molecular dynamics（MD）simulation results indicate that the sodium ions could diffuse in the molecular crystal lattice along the b-axis direction.The energy storage mechanism of SINDIG could be considered as sodium ions intercalated into the molecular crystal lattice.The theoretical method is proved reliable to predict other novel organic electrode materials,and to explore the mechanism of the energy storage.At the end of this paper,the theoretical prediction methods of organic cathode materials are summarized and forecasted.