Phase Change Material Research And System Optimization For Thermal Management Of Lithium-ion Batteries

As lithium-ion batteries are increasingly widely used in new energy vehicles,their safety has been attracted more attention.At the same time,phase change materials(PCM) as a new type of energy storage material are widely used in heat dissipation systems,and composite phase change materials(CPCM) can improve the thermal conductivity of the material.In order to explore the role of composite phase change materials in improving the safety of lithium-ion battery thermal management systems,this paper has carried out several aspects of work and reached the following conclusions:(1)The NTGK model was used to simulate the discharge heat generation behavior of a single lithium-ion battery,and the thermal runaway model was used to simulate the thermal runaway process of the battery.It was found that the thermal runaway of the battery occurred when the temperature reached 150°C,and it first appeared in the center of the battery.The lower the emissivity of the battery surface,the more prone to occur thermal runaway.(2)The phase change and VOF model was used to simulate the melting process of paraffin/silver nanoparticle in the vertical C-TES system,which was in good agreement with the experimental results.During the melting process of paraffin,the heat flux on the wall gradually decreased,and the heat storage capacity of the PCM first decreased,then stabilized,and finally dropped to zero.Adding 0.5?2wt% of silver nanoparticles could accelerate the phase change heat storage process but would reduce the latent heat.(3)The mixture model of multiphase flow was used to simulate the high-temperature melting state of the composite phase change material(CPCM).An appropriate addition of 0.5?2wt% of nano-silver particles could enhance the heat transfer characteristics,and at the same time reducing the size of the silver nanoparticles was conducive to uniform particle distribution.Under high Rayleigh number,the concentration change has little effect on the uniformity,and increasing the concentration will reduce the uniformity of nanoparticles.(4)The thermal management model of paraffin/nano-silver CPCM was established.The battery spacing of 6.5mm could maximize the advantages of PCM.When the mass fraction of nanoparticles was 1%,the effectiveness of nanoparticles to enhance heat conduction was the highest.Compared with air cooling,phase change cooling reduced the maximum temperature of the battery and improved the uniformity of the battery temperature.(5)Constructed a large-scale lithium-ion battery heat dissipation system with a copper foam framework.When the porosity of the copper foam was 90%,the temperature uniformity of phase change cooling under high-rate discharge was stronger than that of air cooling,and the maximum temperature difference inside the battery was only 1.34?.At the same time,compared with the air-cooled system,the phase change thermal management system had the advantage of slowing down thermal runaway,which delayed the time of thermal runaway diffusion by 1610 s.