The Preparation And Characterization Of Boehmite/Polyacrylonitrile Composite Nanofiber Separator

Lithium ion battery?LIB?,as an excellent energy storage device with high energy density,no memory effect,long life cycle,low self-discharge and environmental protection features,is widely used in laptops,digital cameras,smart phones and other mobile devices.At the same time,lithium-ion batteries make them the most promising as large power sources for electric cars and emerging smart grids.Separator is a significantly important component of lithium ion battery.Although it does not directly participate in the electrochemical reaction of the battery,it has important effects on the safety performance and electrochemical performance of the battery.Not only can it effectively separate the positive and negative electrodes of the battery to prevent internal short circuit,but also it can provide an effective channel for the transmission of lithium ions.At present,commercial separators are mainly polyolefin micro-porous membranes,such as polyethylene?PE?and polypropylene?PP?membranes.However,such separators suffer from the poor electrolyte wettability and low thermal stability,which will have adverse impact on the electrochemical and safety performances of batteries.Recently,nanofiber separators prepared by electrospinning have aroused great attention for membrane researchers,owing to their unique three-dimensional network structure and excellent properties including large specific surface area,high porosity and excellent electrolyte uptake.As battery membranes,they can enhance the ionic conductivity and improve the cycle and C-rate performance of the batteries.In this paper,the stable boehmite sol was prepared by sol-gel method using aluminum alkoxide as precursor,and then it was combined with polyacrylonitrile?PAN?solution to form homogeneous spinning solution.The boehmite/polyacrylonitrile?BM/PAN?composite nanofiber membrane was prepared via the method of electrospinning.The surface morphologies and structures of samples were characterized by scanning electron microscope?SEM?,Fourier infrared tester?FTIR?and X-ray diffraction?XRD?.The thermal stability was measured by differential scanning calorimetry?DSC?and thermogravimetric analyzer?TG?.Wettability and mechanical properties were conducted by the contact angle test and the tensile test,respectively.Moreover,the electrochemical performances,including ionic conductivity,electrochemical stability window,cycle and C-rate,of the batteries assembled with separators were carried out by the electrochemical workstation and the battery testing system.The experimental results show that the boehmite/polyacrylonitrile?BM/PAN?composite nanofiber membranes have higher porosity,larger electrolyte uptake,better thermal stability,and the batteries containing these samples exhibit more excellent electrochemical performances compared to PP membrane.Particularly,the 30 wt%BM/PAN membrane possesses the optimal comprehensive performances.Batteries containing the 30 wt%BM/PAN membranes display the highest ionic conductivity(2.85 mS cm^-1),the widest electrochemical stability window?5.5 V vs Li⁺/Li?and the lowest interface resistance?84??,leading to the highest initial discharge capacity(162 mAh g^-1)and the largest capacity retention ratio?90.7%?at 0.5 C after 100 cycles.These findings reveal that the BM/PAN composite nanofiber membranes can be used as potential candidates of commercial separators for high performance LIBs.