Properties And Application Of MOF/RGO Based Composite Phase Change Material In A Lithium-ion Battery Thermal Management System

The electric vehicle industry is developing rapidly under the realistic thrust of energy crisis and environmental pollution.As one of the most ideal power sources for electric vehicles,lithium-ion batteries（LIBs）have potential safety hazards such as combustion and even explosion caused by poor thermal stability.An efficient battery thermal management technology can effectively improve the safety and reliability of the battery pack and ensure that the maximum temperature(T_max)and maximum temperature difference(△T_max)of the battery pack are within a reasonable operating temperature range.In recent years,the phase change material（PCM）for thermal management of LIB has great advantages and has attracted much attention.However,pure PCMs generally have the defect of low thermal conductivity,which is not conducive to the heat dissipation of battery pack.In addition,the PCMs has strong flow ability after endothermic melting,and there is a risk of leakage from the battery module.In this study,a new type of shaped composite phase change material（CPCM）for battery thermal management was developed by using porous materials and thermal conductive additives to enhance PCM:（1）MOF porous carrier（MIL-101（Cr）-NH₂）and reduced graphene oxide（RGO）thermal conductive fillers were prepared.The pore structure and microstructure of MOF were characterized by ASAP and BET tests.It was found that MOF exhibited crystalline porous characteristics,and most of the pores were micropores.Moreover,MOF exhibits big BET specific surface area（1807.4708m²/g）and specific volume（1.442262cm³/g）.The results show that MOF has high adsorption capacity and can accommodate many objective molecules.The chemical properties of RGO were tested by XRD,FTIR and Raman,and it was found that high-quality RGO was successfully prepared.Finally,the thermal properties of MOF and RGO were tested by TGA.MOF and RGO have strong thermal stability in the normal operating temperature range of LIBs.（2）CPCMs were prepared and their thermal properties were characterized by various test methods.First,4 different MOF/RGO/PW（paraffin wax）CPCMs were prepared,and then the optimal ratio was determined to be 35:5:60 by BET and SEM tests.The structure of CPCMs was characterized by XRD,FTIR and XPS,which confirmed the successful preparation of MOF/RGO/PW CPCMs.Finally,DSC,TGA,Hot Disk and heat resistance test results show that CPCM with 60%PW（CPCM-60%PW）has excellent thermophysical properties:the melting enthalpy of CPCM-60%PW after 500 thermal cycles is 80.55 J/g,which is close to its theoretical value;the thermal conductivity increased by 472%compared with pure PW;The thermal stability of PW is greatly improved.（3）The CPCM-60%PW was embedded in a LIB pack and its enhanced heat transfer characteristics were experimentally studied.Thermal management experiments were carried out on battery modules cooled by CPCM-60%PW under different working conditions and compared with natural air cooling.The results show that with the increase of ambient temperature or discharge rate,the T_max rise trend of CPCM cooling module is significantly slowed down,indicating that CPCM-60%PW has excellent temperature control performance.In addition,different from natural air-cooled battery module,the△T_max of the CPCM battery module decreases with the increase of ambient temperature,which is attributed to the high thermal conductivity of CPCM-60%PW.The application of CPCM-60%PW in the cooling system of battery module can not only control the peak temperature,but also balance the temperature uniformity,showing excellent thermal management performance.CPCM-60%PW was also compared with some other CPCMs and found that the excellent thermal management performance of CPCM-60%PW is particularly reflected in particularly reflected in high discharge rate/high ambient temperature that is prone to thermal runaway in the battery pack.（4）After the completion of all thermal management experiment,the anti-leakage performance of CPCM-60%PW was tested by TGA.The results show that there is no PW leakage during the whole experiment,and CPCM-60%PW has excellent anti-leakage performance,which confirms the practical feasibility of introducing MOF-based CPCMs into battery thermal management system.The research in this paper can provide theoretical support and technical guidance for the engineering application of MOF-based CPCMs in the field of LIB thermal management.