| As an energy storage device with excellent performance,lithium-ion batteries have been widely used in electronic products,transportation,aerospace and other fields because of their high energy density,long cycle life,and no memory effect.As one of the important components of lithium ion battery,the performance of separator directly affects the safety performance and electrochemical performance of the battery.At present,commercial lithium-ion battery separators are mainly polyolefin separators based on polypropylene(PP)and polyethylene(PE),but the type of separator has the inherent defects of poor electrolyte wettability and low thermal stability.As a result,the electrochemical performance and safety of the battery are limited.Therefore,the development of high-performance separators that can replace polyolefin separators is of great significance to the improvement of lithium-ion battery performance.Polyarylethersulfone is a kind of non-crystalline polymer material,which has good film-forming properties and chemical stability,and contains polar groups such as sulfone group(-SO2-)in the molecule.It is used in automobiles,electronics,medical,separators and other fields have a wide range of applications.However,with the development of the period and technology,traditional polyarylethersulfone has been difficult to meet some performance requirements,so the development of polyarylethersulfone with higher thermal stability and better chemical properties has attracted people's attention.In this paper,a new type of polyarylethersulfone made in the laboratory is used as the separator material,and a lithium-ion battery separator with large porosity and liquid absorption is successfully prepared by the non-solvent-induced phase inversion(NIPS)method.In order to further improve the thermal stability of the separator,this paper uses the characteristics of phase change materials that can absorb and store the surrounding heat during phase change,and incorporate phase change paraffin and phase change microcapsules into polyarylethersulfone respectively.Thus,a new type of composite separator with phase change function is prepared,which aims to improve the safety performance and electrochemical performance of the separator.The main research results are as follows:1.Using BDD as the raw material(the model of polyarylethersulfone is BDD),the BDD series separator was prepared by the NIPS method.The influence of different separator-forming conditions on the pore structure and physical and chemical properties of the separator was explored.And then the best separator-forming conditions were obtained:the solvent is triethyl phosphate(TEP),the polymer concentration is 20wt%,the coagulation bath is water/isopropanol=4/6,and the residence time of the casting liquid in the air is 20s.The separator under the best separator forming conditions has a uniform sponge-like pore structure,and the liquid absorption,porosity and ionic conductivity are significantly higher than commercial PP membranes.At 180°C,the PP separator has completely shrunk,while the BDD separator has not undergone significant thermal shrinkage.After being assembled into a button battery,the specific discharge capacity of the battery assembled with the BDD separator is higher than that of the PP separator at the same current density.The initial discharge specific capacity at 0.5C current density is 135.6 m Ah g-1,which is higher than the 113.8m Ah g-1 of the PP separator.After 100 cycles,the capacity retention rate is 92.3%,which is higher than 90.8%of the PP separator.2.Phase change material(PCM)is a material that changes physical properties with temperature changes and realizes the absorption or release of surrounding heat.In order to further improve the thermal stability and electrochemical performance of the separator,the phase change material—paraffin wax is introduced by blending under the optimal separator forming conditions,and the BTD series separator(the model of polyarylethersulfone is BTD819)is prepared by the NIPS method.Compared with the BTD-0%separator,the porosity,liquid absorption and ionic conductivity of the BTD-10%separator have been significantly improved.The thermal shrinkage of the BTD-10%separator placed at 220°C for 30 minutes is 34.8%lower than that of the BTD-0%separator.The melting enthalpy and crystallization enthalpy of BTD-10%are 4.25 J/g and 5.12 J/g,respectively.At room temperature,the specific discharge capacity of button batteries assembled with BTD-10%separator is higher than that of BTD-0%separator at the same current density.The capacity retention rate of the BTD-10%separator is 94.91%after 100 cycles at 0.5C current density,which is 4.13%higher than that of the BTD-0%separator.In the cyclic test at 120°C,the battery assembled with the PP separator will fail quickly,the capacity retention rate of the BTD-0%separator drops to81.96%,and the capacity retention rate of the BTD-10%separator is 86.16%.3.In order to improve the shortcomings that paraffin wax is easy to leak when the solid-liquid phase transition occurs,resulting in a low latent heat of phase transition,and the shortcomings of incompatibility with polyaryl ether sulfone when the content is high.And in order to further improve the thermal stability and electrochemical performance of the separator.Phase change paraffin is encapsulated by microencapsulation to make phase change microcapsules,which are blended with polyarylethersulfone(the model of polyarylethersulfone is BTD415),and the BTDM series separator is prepared by the NIPS method.Compared with BTDM-0%separator,the porosity,liquid absorption and ionic conductivity of BTDM-30%separator are significantly improved.The heat yield of BTDM-30%separator placed at 220°C for 30 minutes is 63.7%lower than that of BTDM-0%separator.The melting enthalpy and crystallization enthalpy of BTDM-30%separator are 25.24J/g and 26.13 J/g,respectively.At room temperature,the specific discharge capacity of button batteries assembled with BTDM-30%separator is higher than that of BTDM-0%separator at the same current density.The capacity retention rate of the BTDM-30%separator is 2.02%higher than that of the BTDM-0%separator after being cycled for 100 cycles at a current density of 0.5C.In the cyclic test at 120°C,the battery assembled with the PP separator will fail quickly,the capacity retention rate of the BTDM-0%separator drops to 82.15%,and the capacity retention rate of the BTDM-30%separator is 90. |
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