| Lithium-ion battery has become one of the most widely used energy batteries because of its high energy density,high operating voltage,long cycle life and low self-discharge rate.As an important component of lithium-ion battery,battery separator has a great impact on the safety,cycle lives,energy density and power density of the battery.Therefore,the design and development of high-performance battery separator has become the current research focus.Due to its excellent porosity,large specific surface area and unique pore structure,the electrospun nanofiber membrane(NFM)can absorb a large number of liquid electrolytes and provide effective conductive channels.It has been widely studied as a separator for lithium-ion batteries.However,the traditional singleneedle electrospinning technology has low preparation efficiency,and the disordered fibers collected have defects such as isotropic and poor mechanical properties,which limits the practical application of electrospun NFMs in lithium-ion battery separator.In this paper,based on the funneling air-jet electrospinning device(FAJE),an improved funneling air-jet electrospinning device(IFAJE)was proposed to obtain aligned nanofibers with higher yield and quality.The spinning mechanism and effect of batch preparation of polyacrylonitrile(PAN)nanofibers by IFAJE were studied by combining theoretical analysis and experimental tests.At the same time,the optimal spinning parameters of IFAJE device were investigated,and high-quality aligned NFMs were obtained.On this basis,the aligned PAN-based NFMs obtained from the optimal spinning parameters were applied to the lithium-ion battery separator,and their thermal stability,electrolyte affinity and related electrochemical performance were tested to explore their advantages as lithium-ion battery separators.The details are as follows:(1)Ansoft Maxwell 3D software was used to simulate the electric field distribution in the spinning processes of FAJE and IFAJE respectively,and their spinning mechanism was compared and studied.Meanwhile,the spinning effects of these two spinning devices for the batch preparation of aligned PAN NFMs were experimentally studied to verify the correctness of the numerical simulation results.On this basis,the optimal spinning parameters of IFAJE device were investigated to obtain high-quality and high-yield aligned NFMs.The results showed that because the IFAJE device made full use of the"tip discharge" effect,its electric field distribution had the advantages of more orderly electric field direction,more uniform electric field distribution,and higher electric field intensity,which enabled it to prepare NFMs with higher quality,yield and alignment.The experimental results were in agreement with the simulation results.At the same time,it was found that when the relative concentration of PAN in the spinning solution was 11 wt%,the spinning voltage was 45 kV,and the rotation speed of the drum with the diameter of 16 cm was 400 r/min,the spinning effect was the best,and the aligned nanofibers obtained had the highest quality and higher yield.(2)The morphology,structure and performance of aligned PAN NFMs prepared in batches by IFAJE device under the optimal parameters were characterized and tested.Then,the aligned PAN NFM was used as a lithium-ion battery separator,and its thermal stability,electrolyte affinity and related electrochemical performance were tested.The advantages of the aligned PAN NFM as a separator for lithium-ion battery were explored by taking disordered PAN NFM and commercial PP membrane as the controls.The results showed that the mechanical strength,porosity,electrolytic affinity,ionic conductivity,lithium-ion transference number and electrochemical stability of the aligned PAN membrane are better than those of disordered PAN membrane.And the porosity,thermal stability,electrolytic affinity and related electrochemical properties of the two PAN membranes are better than those of PP membrane.Therefore,the lithium-ion battery assembled with the aligned PAN membrane had the most excellent rate and cycling capabilities.(3)The aligned PAN/PMMA NFMs with different ratios of PAN and PMMA(PAN:PMMA=6:4,7:3,8:2 and 9:1)were prepared in batches by IFAJE device,and the optimal ratio was determined to be 7:3.On this basis,the aligned PAN/PMMA/singlewall carbon nanotubes(SWCNTs)composite NFM was prepared in batches,and it was compounded with PP membrane to make a double-layer membrane(PAN/PMMA/SWCNTs//PP)for lithium-ion batteries.And the advantages of PAN/PMMA/SWCNTs//PP membrane as a lithium-ion battery separator were explored.The results showed that the mechanical properties of PAN/PMMA membrane were better than those of PAN membrane,but its thermal stability was poor,which leaded to the instability of its electrochemical performance and affects the electrochemical performance of lithium-ion battery assembled using the PAN/PMMA membrane as a battery separator.The aligned PAN/PMMA/SWCNTs membrane prepared on this basis improved the thermal stability of the separator,the mechanical properties,porosity,electrolyte affinity and related electrochemical properties of the separator.However,due to its certain conductivity,it could not be used as the battery separator alone.Therefore,PAN/PMMA/SWCNTs membrane was superimposed with PP membrane to obtain PAN/PMMA/SWCNTs//PP.The battery assembled with the separator had better electrochemical stability,rate and cycling capabilities,indicating that PAN/PMMA/SWCNTs//PP was a potential high-performance lithium-ion battery separator. |
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