Preparation Of Composite Phase Change Material With Room-temperature-flexibility And Its Application In Battery Thermal Management

Phase change thermal storage technology has become one of the important technologies of battery thermal management(BTM).In order to meet the demands of engineering applications,polymer components are usually added into phase change materials(PCM)to greatly improve the formability/processability and cycle stability of composite PCM(CPCM),such as polyethylene,polystyrene and epoxy resin.However,the traditional CPCM possesses defects like strong rigidity and high contact thermal resistance.In order to reduce the contact thermal resistance between composite phase change materials and batteries,flexible composite phase change materials(FCPCMs)developed in recent years are believed to effectively minimize the thermal contact resistance in battery thermal management application compared to rigid CPCMs.However,these“thermally-induced”flexible CPCMs only present well-flexibility above the phase change temperature(PCT),which still leads to compressive stress accumulation,and is unfavorable to the flexible assembly of the cells and battery modules with variable specifications under normal operating temperature.Herein,a novel kind of flexible CPCM with well-retained flexibility in a much wider temperature range is prepared by carefully selecting a copolyester thermoplastic elastomer with polyether soft segment(TPC-ET)to replace the conventional olefin block copolymer(OBC)skeleton.The internal rotation resistance of the ether bond(C-O-C)in TPC-ET is much lower than the C-C bond in OBC,thus giving rise to a much better flexibility,especially under room and low temperatures from 20 to-5?.Therefore,the obtained TPC-ET based flexible CPCM shows outstanding applicability and cooling performance to various cells and battery modules through facile installations,such as cylindrical cells with different dimensions,as well as cylindrical,prismatic and pouch battery modules.On the other hand,another flexible and controllable phase change materials were prepared by copolymerization of methyl methacrylate(MMA)and butyl acrylate(BA)as hard monomers and soft monomers respectively,and their flexibility and temperature control properties were studied.The main research contents and conclusions of this thesis are as follows:(1)A new flexible composite phase change material(FCPCM)was successfully prepared by constructing a TPC-ET blending material instead of conventional OBC with ensuring a certain proportion of PA and EG,which possesses high thermal conductivity and well flexibility at room temperature.It can reduce the contact thermal resistance between phase change material and battery,and realize flexible assembly of batteries and battery modules with different specifications.The results show that the latent heat and thermal conductivity of fcpcm increase with the content of PA and EG.When the content of PA,EG and TPC-et are 45wt%,10wt%and 45wt%,respectively,the latent heat and thermal conductivity of the FCPCM are 102.4 J g^-1and 1.64 W m^-1K^-1,respectively.The samples shows an anti-leakage performance of less than 0.1wt%and a good flexibility at room temperature or even low temperature.(2)14650 single cell,18650 single cell,26650 single cell,32650 single cell,18650 cell module,prismatic battery module,pouch battery module and ternary prismatic battery module were adopted as the research object of thermal management.In order to study the cooling effect of FCPCM,different discharge rates of 1C,2C and 3C were used.The test results show that FCPCM provides better heat dissipation performance,especially under the discharge rate of 3C,the maximum temperatures of 14650,18650,26650 and 32650 cells with air natural convection are 44.9?,44.6?,54.8?and 56.0?respectively,and the maximum temperatures with FCPCM cooling are 42.1?,42.0?,45.3?and 46.0?respectively.On the other hand,the highest temperatures of 18650 battery module with air convection,LDPE-based CPCM cooling and FCPCM cooling are 58.6?,55.5?,and51.5?,respectively.Similar test results can also be reflected in the charging and discharging process of prismatic battery module and pouch battery module,indicating that FCPCM has excellent heat dissipation performance.In addition,the FCPCM coupled with liquid copper cooling plate(FCPCM/LCP)was applied to the thermal management investigation of ternary battery module.With this cooling strategy,the maximum temperature of the module decreased from 90.8?to 58.5?and the maximum temperature difference decreased from 36.6?to 9.6?at 3C discharge rate.(3)Another PA/EG/P(MMA co BA)flexible composite phase change materials were prepared by using MMA and BA as comonomers,and the flexibility of the materials could be controlled by adjusting the MMA/BA ratio.When the mass fraction of PA,EG,BPO,MMA and BA were 44,7,1,19.2 and 28.8wt%,respectively,The phase change temperature,latent heat and thermal conductivity are 48.1?,93.57 J g^-1and 1.12 W M^-1K^-1,respectively.The experimental results are close to the theoretical values,because the reaction is carried out at low temperature,the paraffin almost does not volatilize,and there is no chemical reaction between P(MMA co BA),PA and EG in FCPCM.The flexural modulus can be tailored in a wide range from 2.58 to 52.14 Mpa by changing the MMA/BA ratio.At the discharge rate of 5C,the maximum temperature of the prismatic battey cooled by PA/EG/P(MMA co BA)is 46.0?,and the maximum temperature of the prismatic battery cooled by nature air convection is 47.2?.