Preparation Of Hydrated Salt Composite Phase Change Material And Its Application In Lithium-ion Battery Thermal Management

At present,the performance degradation and the thermal runaway risk caused by the sensitivity of lithium battery to temperature seriously affect the safety of lithium battery.Previous studies found that phase change materials could provide a suitable temperature environment for the battery by the characteristic of holding a constant temperature in the process of phase change process.However,in the lithium-ion battery thermal management,the flammable organic phase change materials will bring greater fire hazard during the process of lithium-ion battery thermal runaway.In this thesis,the mixed system of hydrated salts with suitable phase change temperature in lithium-ion battery thermal management is selected by phase diagram prediction and experimental of Na₂SO₄·10H₂O and KAl（SO₄）₂·12H₂O mixture.Then the hydrated salt/polyurethane foam composite phase change material is prepared by adding high thermal conductivity expanded graphite with rich pores and polyurethane foam with good processability as support materials.The thermal management and thermal runaway barrier properties of this material in lithium-ion battery are comprehensively analyzed.The main contents are as follows:1.The phase diagram of the mixed hydrated salts Na₂SO₄·10H₂O and KAl（SO₄）₂·12H₂O is predicted using the modified BET model.This study shows that the phase change points of hydrated salt mixture could be adjusted continuously by changing the proportion of the hydrated salts even without eutectic phenomenon.Besides,Na₂SO₄·7H₂O is generated during the phase change process of hydrated salt mixture,which affects the phase change properties.2.A series of Na₂SO₄·10H₂O and KAl（SO₄）₂·12H₂O mixed hydrated salts are prepared and analyzed,and the suitable ratio of hydrated phase change materials for thermal management of lithium-ion batteries is obtained.The study shows that the phase diagram can effectively predict the trend of change points and composition variation,and the phase separation of hydrated salts is influenced by the substance changes during phase change process.When the ratio of Na₂SO₄·10H₂O to KAl（SO₄）₂·12H₂O is 3:7,the mixed hydrated salt system has a suitable phase change performances to applicate in battery thermal management.3.Hydrated salt/polyurethane composite phase change materials is prepared by impregnation,and phase composite phase change materials with good phase change and flame-retardant properties are obtained by the analysis of phase change process and flame performance.The study showes that the phase change properties of the hydrated salt phase change material are preserved in the hydrated salt/polyurethane composite phase change materials.When the content of expanded graphite is 4 wt.%,the thermal conductivity of the composite phase change material is 1.390 W/（m·K）,and the phase change enthalpy is 226.89J/g,which has excellent flame-retardant properties simultaneously.4.In the battery thermal management experiments and thermal runaway experiments,the hydrated salt/polyurethane composite phase change material shows good thermal management performance and excellent battery thermal runaway blocking performance.Compared with natural cooling,the battery thermal management using phase change material could reduces the maximum temperature of the battery by 16.0%,20.4%and 17.1%respectively at 1C,1.5C and2C discharge rates,and the temperature difference decreases by 38.2%,59.7%and 54.2%respectively,which means the satisfy thermal management properties.In addition,the risk of battery thermal runaway induced by external high temperature environment could be reduced by phase change materials,and the thermal runaway propagation could also be blocked effectively.