| The rapid development of new energy vehicles has made lithium-ion batteries with high energy density and high stability the main power source,and electrodes are the key factors determining the above performance.In order to visualize the microstructural parameters,the structure of the electrode needs to be accurately mathematically described;The electrochemical reaction and material transport inside the electrode will be accompanied by heat generation,and the heat generation source,real-time heat production rate and local microstructure in different areas of the battery are different,so that the heat transfer of the battery is uneven,resulting in excessive local temperature.Therefore,this paper uses fractal theory to describe the structure of porous electrodes,couple electrochemistry with temperature field,and study the heat production characteristics of batteries.The main research contents are as follows:(1)The porous electrode has fractal characteristics,considering the influence of microstructure parameters on internal mass transfer,the mathematical model of the effective diffusion coefficient of lithium ions in the solid and liquid phases is derived,the degree of influence of the solid and liquid diffusion rate and electrochemical rate by the structural parameters of the porous electrode is studied,and the relationship between the size and distribution of active particles and the discharge capacity is explored.(2)Combined with the electrochemical reaction process of lithium-ion batteries and the change of temperature in the thermal model,a micro-macroscale thermal-chemical coupling model was established,the changes of heat production of each component at different discharge moments in the safety life cycle of lithium-ion batteries were studied,the heat generation power of the positive and negative electrodes and separators of the battery was quantitatively analyzed,and the differences in the heat production characteristics of different regions of the battery were explored.(3)Based on the uneven real-time heat production and transfer of a single cell,the temperature changes of the gapless battery pack at different times are simulated,the reasons for temperature aggregation in the battery pack are analyzed,the influence of heat exchange area and circulation on the heat dissipation of the battery is discussed,and the position distribution of the single cell in the battery pack is optimized in order to prevent the by-decomposition reaction between the electrode cathode material and the electrolyte.The results show that the effective diffusion coefficient of lithium ions in the solid and liquid phases increases with the increase of particle size ratio,and the discharge capacity obtained by considering the microstructure parameters is more realistic than that obtained by bruggeman factor.In the process of increasing the discharge rate from0.5C to 5C,the proportion of heat yield of the positive electrode to the total heat yield increases,and the proportion of heat generation rate of the diaphragm also increases.The reversible heat fluctuation trend in the positive and negative electrodes is large,and the change trend of irreversible heat and ohmic heat is relatively flat,so the total heat yield of the positive and negative electrodes changes with the reversible heat fluctuation of their respective reversible heat.The temperature of the gap-free battery pack is high and the distribution is uneven,and the battery pack with a gap of 10 mm and 20 mm increases the heat exchange area and circulation,and its overall temperature is reduced by 1.1% and 1.8% respectively compared with the gap of 0mm,and the unevenness of temperature distribution is reduced.In order to avoid exceeding the critical temperature of the decomposition reaction between the cathode material and the electrolyte,it is necessary to reasonably optimize the position distribution of single cells in the battery pack. |
PDF Full Text Request