The Thermal-chemo-mechanical Coupled Theory And Finite Element Analysis Of Electrode Materials In Lithium-ion Batteries

The electrodes play important roles in the voltage and cycle life of lithium-ion batteries(LIBs).The focus of LIBs is mainly on design of electrode and improvement of electrochemical performance in LIBs and so on.While the researchers gradually explore volume deformation of electrode with electrochemical performance in LIBs recently during charge and discharge process,the electrode stress is mainly attributed to the diffusion of lithium and the nonuniformity of temperature.The energy density,cycle life and power density of LIBs are closely related with the stress of electrode,which can cause electrode damage and lead to capacity fade of LIBs by such large amount of stress,and finally the LIBs will be failure.In order to understand the evolution of concentration and stress with lithiation essentially,this thesis combines theoretical analysis with numerical simulation to study concentration field and stress field of electrode based on temperature field theory of LIBs.We present the chemo-mechanical theory model to study concentration field and stress field of LIBs and electrode materials.The main research work of this thesis includes the following aspects:(1)We suggesting an electrochemistry-thermal coupling model to study the temperature field of electrode.We analyzed the temperature evolution with different thermal conductivity and surface heat emissivity in the finite element software.We find that with the thermal conductivity and surface heat emissivity increasing,the temperature of electrode in LIBs will decrease.(2)We present the chemo-mechanical lithiation model to study concentration field and stress field of electrode.We analyzed the concentration and stress evolution for the hollow core-shell and film structural Si electrodes with isotropic and anisotropic in the finite element software.We find that the value of ?? with anisotropic is larger than the isotropic one for a hollow core-shell structural electrode,which can easily cause Si electrode damage.(3)We suggesting an thermal-chemo-mechanical coupling model to study concentration field and stress field of electrode.We analyzed the concentration and stress evolution with different charge conditions for a hollow core-shell structural LiyMn2O4 electrode in the finite element software.We find that the value of ?? is increasing with curvature a/b decreasing under galvanostatic condition,which can easily cause the LiyMn2O4 electrode damage.We find that the value of ?? is increasing with curvature a/b increasing under potentiostatic condition,which can easily cause the LiyMn2O4 electrode failure.In addition,we present an thermal-chemo-mechanical coupling model to study concentration field and stress field of two spherical LiyMn2O4 positive particles contact each other.We find that the concentration in the area of particles contact each other is lower than other area,due to the compressive stress in the area of particles contact each other is larger than other area,the larger compressive stress reduce the lithium-ion enter.