| With the rapid development of new energy vehicle industry,the demand for highperformance lithium-ion power battery is very urgent.However,serious diffusion polarization and diffusion stress will be generated inside the lithium-ion battery by improper external use or unreasonable design of internal structure,which will cause battery capacity decline and electrode structure failure.Based on the theory of electrochemistry and diffusion mechanics,the main factors affecting the diffusion polarization and diffusion stress of lithium-ion battery were studied in this paper by the method of test and simulation,which can provide theoretical basis for reducing the battery polarization and stress and guide the structure design of battery.The main research contents and conclusions of this paper include the following aspects:(1)The tests of the ternary lithium-ion battery were carried out to obtain the characteristic parameters of the battery,including capacity calibration test,charge and discharge test at different current rates and ambient temperatures,HPPC(Hybrid Pulse Power Characteristic)test and electrode reference potential test,and the electrochemical characteristics and polarization internal resistance characteristics of the battery under different conditions were obtained through tests.The results show that the battery discharge at the large current rate or low temperature environment will cause the voltage to drop rapidly and the discharge cut-off capacity to decrease.In addition,the ohmic and polarization internal resistance of the battery show an increasing trend with the depth of discharge as a whole,and the trend is more significant under the low temperature environment.(2)Based on the electrochemical and diffusion mechanics principles of lithiumion batteries,the electrochemical-stress coupling model of lithium-ion battery was constructed by COMSOL software,and the key parameters of the model were modified.According to the coupling principle,the solid-phase diffusion stress of electrode is closely related to the electrochemical characteristics.Therefore,the indirect verification method is adopted in this paper,which is to use the discharge test under different conditions and HPPC test to verify the model under different currents,different ambient temperatures and dynamic current condition.The results show that the accuracy and adaptability of the model are well,and the maximum error is less than 4%.(3)Based on the model,the method of single factor quantitative analysis was used to systematically study the influence process and mechanism of the diffusion polarization in solid and liquid phases of positive and negative electrodes caused by internal and external factors,and the influence of the main factors on the discharge performance was further discussed.External factors include discharge rate and ambient temperature,and electrode thickness and particle radius are included as internal factors.The results show that the high rate and low temperature will increase the diffusion polarization in solid and liquid phases,and it is more serious at low temperature.The positive and negative electrode thickness and the negative electrode particle size are the main internal factors that affect the diffusion polarization,and the positive electrode thickness is the key factor that affects both the diffusion polarization and the discharge performance.(4)Based on the model,the internal stress distribution in the negative electrode particle was obtained from the distribution of solid-phase lithium ion concentration,and the influence rules and internal mechanisms of external factors and electrode material properties on the diffusion stress in the electrode particle were further systematically analyzed.The properties of electrode materials mainly involve the elastic modulus,Poisson’s ratio,porosity,particle size and thickness.The results show that the negative electrode particles shrink during discharge,the center of the particle is subjected to the hydrostatic stress,while the surface is subjected to the maximum tensile stress and is prone to fracture at the end of discharge.The external factors have a great influence on the internal stress of the particle,and the porosity and particle size of the electrode material are the main internal factors that affect the diffusion stress in the particle,which should be fully considered in the design of the electrode. |
