Characteristics Analysis Of Magnesium Ion Batteries Based On Molecular Dynamics And Finite Element Method

At present,the development of electric vehicles is mainly limited by the safety,high battery cost and short range,which brings new challenges to the research and development of power batteries.However,Li-ion batteries have encountered bottlenecks in the development process,and it's difficult to break through the energy density limitation of Li-ion batteries.Because magnesium metal has the advantages of high energy density,natural abundance and low cost,rechargeable magnesium batteries(RMBs)have emerged as a considerable candidate.A growing number of researchers have begun to study rechargeable secondary batteries based on magnesium ions,to meet the demand for sustainable,high-performance,and low-cost energy storage devices.This article aims to conduct a multi-scale modeling and analysis of magnesium-ion batteries through molecular dynamics and finite element methods,and then establish the relationship between the microscopic material selection and the analysis of the electrochemical performance and thermal characteristics of the single-cell.Firstly,molecular dynamics simulation was used to study the influence of alloy anode materials on the structure of electrolyte and transport performance of magnesium ion battery,and the relationship between electrode material and performance was established.Secondly,the influence of electrolyte composition and ambient temperature on cell transport and electrolyte structure was further studied.Finally,an electrochemical-thermal coupling model of the magnesium ion battery was constructed by combing the parameters obtained by molecular dynamics simulation with the finite element method.The electrochemical performance and thermal characteristics of single-cell during the discharge process were studied by simulation calculation of the model.The main research contents and results are as follows:(1)The effects of the types and proportions of alloying elements in the alloy anode of magnesium ion battery on the transport performance and electrolyte structural characteristics of magnesium ion battery are studied.Four types of negative electrode materials are mainly used:pure magnesium,Mg-Al alloy,Mg-Si alloy,Mg-Zn alloy.And the addition ratio of each material in the electrode is 3%,6%,and 9%,respectively.This paper compares the number density,electrode potential,and diffusion coefficient of battery systems using different electrodes to explore the mechanism of the influence of negative electrode materials on battery performance.The battery with magnesium-silicon alloy anode shows better performance among different magnesium-ion battery systems.(2)The influence of electrolyte composition ratio,electrolyte concentration,and working temperature on the transport performance and structural characteristics of magnesium ion battery electrolyte is studied.Base on the advantages and disadvantages of organic electrolyte and inorganic electrolyte,this paper mixes the organic electrolyte Mg(TFSI)₂ and inorganic electrolyte Mg Cl₂ to construct a new electrolyte calculation model,to combine the advantages of both.For electrolytes of different compositions and concentrations,the ionic diffusion coefficient and radial distribution function were calculated respectively.The electrolyte with a concentration of 1M and a mixing ratio of 1:1 performed better on the transport performance.The electrolyte is also simulated at different working temperatures.The electrolyte transport performance is sensitive to temperature,and the temperature range for high-performance work is narrow.(3)The electrochemical and thermal coupling model of magnesium-ion battery was established,and the transport parameters obtained from the molecular dynamics simulation in Chapter 3 were taken as the input parameters of the finite element model to simulate the electrochemical and thermal characteristics of magnesium-ion cell.The changes in the electrochemical characteristics of the battery during the discharge process and the discharge rate and the effects of discharge rate and airflow rate on the heat transfer of the battery were discussed.