Study On Phase Change Composites For Thermal Management Of Li-ion Batteries

In the process of rapid charge and discharge of lithium-ion battery,complex electrochemical reaction occurs inside the lithium-ion battery,and the heat generated increases its temperature.If it cannot be cooled in time,it will lead to fire or explosion and other thermal runaway phenomena.As a new type of battery thermal management technology,phase change materials have high phase change latent heat.Absorbing heat through phase change materials can effectively reduce the peak temperature of the battery,improve the temperature uniformity of the battery pack,and help to improve the thermal safety performance of the battery.At present,paraffin phase change materials have been more studied in the thermal management of lithium-ion batteries,but there are still problems such as easy leakage,flammability and high rigidity.The non-combustible material calcium carbonate is coated with paraffin to form microencapsulated paraffin,which can effectively prevent paraffin leakage.Then,the phase change composites were prepared with flake alumina and silicone rubber as thermal conductivity agent and flexible binder respectively,which gave the phase change composites better thermal conductivity and flexibility.The main contents are as follows:1.Calcium carbonate was deposited on the surface of paraffin particles through self-assembly reaction to form microencapsulated paraffin.The effects of emulsifier concentration,stirring speed and core-wall ratio on the thermal storage performance of phase change microcapsules were investigated.The results showed that when the emulsifier concentration was 10 mmol/L,the stirring speed was 300 rpm and the core-wall ratio was 2:1,the phase change temperature of the phase change microcapsule was 48.68 ~oC,the phase change enthalpy reached 95.75 J/g,and the leakage rate was only 0.28%when it was placed at 60 ~oC for 180min.2.Phase change microcapsules,flake alumina and silicone rubber matrix were uniformly mixed by physical blending method to prepare phase change composites.The micromorphology,heat storage properties,thermal stability and combustion properties of phase change microcapsules composites were studied.The results showed that the phase change microcapsules and flake alumina powder were evenly distributed in the silicone rubber matrix.When the addition amount of phase change microcapsules was 60%,the phase change temperature and enthalpy of phase change composites were 52.26 ~oC and 56.33 J/g respectively,the initial thermal decomposition temperature and carbon residue rate(400 ~oC)were 227.86 ~oC and 80.26%respectively,the ignition time were increased from 675 s to 737 s,and the total heat release and total smoke production were decreased by 19.4 MJ/m~2 and 15.6 m~2 respectively,indicating a low fire hazard.3.The prepared phase change microcapsule composites were applied to the thermal management of lithium-ion batteries,and the thermal management performance experiments were carried out at different ambient temperatures and charge discharge rates.The research shows that when the ambient temperature was 20 ~oC and the charge discharge ratio was 1.5C,compared with natural cooling,the maximum temperature of lithium-ion battery with phase change cooling was reduced from 66.6 ~oC to 53.6 ~oC(decreased by 13 ~oC),and the maximum temperature difference of each battery was reduced from 8.3 ~oC to 6.4 ~oC(decreased by 1.9 ~oC),which significantly improved the temperature uniformity of each battery and played a better thermal management effect.