| Lithium-ion batteries are widely used in portable electronic products such as laptops and mobile phones,and large-scale energy storage equipments such as electric vehicles.In order to meet the complex functions and high-power use of the energy consumption devices and equipments,the overall characteristics of excellent electrochemical performances,good thermal stability,strong adaptability in extreme environments and long service life are essential for advanced lithium ion batteries,which pose new challenges to current battery technology.As a key component of lithium ion batteries,the separator has become a key to comprehensively improve the performance of lithium ion batteries by developing advanced separators owing excellent ionic conductivity,good mechanical properties and electrochemical properties,which is also currently a focus of research efforts.The main work of this paper is to find out the best doping amount by adding the garnet-type Li6.75La3Zr1.75Ta0.25O12?LLZTO?nanoparticles into the polyvinylidene fluoride-hexafluoropropylene?PVDF-HFP?polymer.By changing the preparation process of the separator,coating method and electrophoretic deposition method are adopted to prepare high-performance lithium ion battery separator.The concrete work is as follows:The garnet-type LLZTO nanoparticles were synthesized by solid phase reaction,and then added to polyvinylidene fluoride-hexafluoropropylene?PVDF-HFP?with different mass fractions.Five different mass fractions of LLZTO/PVDF-HFP composite separators were prepared by the coating method.Compared with pure PVDF-HFP separator and Celgard 2325,by studying the microstructure,mechanical properties,ionic conductivity,contact angle,electrochemical properties and other characteristics of these separators,it was found that when adding LLZTO nanoparticles with a mass fraction of 12.8%in PVDF-HFP,the composite separator shows excellent electrochemical performance and stability.The initial discharge specific capacity of the battery up to 156 mAh g-1 at 0.5 C,only 2.25%capacity degradation was observed after 100 charge/discharge cycles,and the ionic conductivity reaches 3.6×10-4 S cm-1 at25°C.In addition,the mechanical properties of the separator and its affinity with the electrolyte are improved by adding LLZTO nanoparticles.The separator of the maximum tensile strength improves from 7.2 MPa to 16 MPa,and the electrolyte contact angle decreased from 26.12°to 9.01°.A novel gel-solid composite high performance lithium ion battery separator was developed by electrophoretic deposition in LLZTO/PVDF-HFP mixed colloidal for the first time.Comparison with pure PVDF-HFP separator developed by electrophoretic deposition in the PVDF-HFP colloidal,and studying the microstructure,liquid absorption rate,porosity,ionic conductivity,mechanical properties and electrochemical properties of the two kinds of separator,it was found that the proper amount of LLZTO doping and electrophoretic deposition changed the microstructure of the PVDF-HFP gel separator and enhanced the mechanical properties of the separator.The maximum tensile strength of the PVDF-HFP separator and the LLZTO/PVDF-HFP composite separator can reach 13.8 MPa and 28.6 MPa,respectively.In addition,LLZTO/PVDF-HFP gel-solid composite lithium ion battery separator also has excellent ionic conductivity and electrochemical performance,whose the ionic conductivity can reach 7.13×10-4 S cm-1,7.46×10-4 S cm-1,9.65×10-4 S cm-1 at 25°C,35°C and 45°C,respectively.The initial discharge specific capacity of the battery up to 152 mAh g-11 at0.5 C,only 2.44%capacity degradation was observed after 100 charge/discharge cycles. |
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