Research On The Electrospinning Preparation Of PVDF/PMMA/BM Lithium Battery Separator

Energy shortage and environmental pollution are two major problems which human beings are facing in the 21 st century. Study on lithium-powered electric vehicles with the advantage of zero emission and renewable energy is one of the most important development directions in the future auto market. The improvement in the properties of diaphragm materials is a necessary requirement of the advancement of commercial lithium electronics. At present, diaphragm materials made in China are relatively poor, and most of high-quality diaphragms rely on imports. PP and PE diaphragms obtained by the existing process have poor thermal stability and low aspiration rate. Nonwovens produced by electrospinning method with 3D micro pore structure have the advantage of large specific surface area, high porosity and aspiration rate, but their strength is still low. The optimal spinning parameters of poly(vinylidene fluoride)(PVDF) were studied in this paper. PVDF/PMMA composite diaphragms were prepared and then the PVDF/PMMA/BM composite diaphragm were also produced by adding boehmite(BM).The result from spinning technology optimization shows that The PVDF diaphragms with the average diameter of 900-1200 nm were obtained under an optimal condition, in which the optimal electro-spinning concentration, voltage,receiving distance and speed of PVDF diaphragms are 12 wt. %, 20 kV, 18 cm and0.002 mm/s, respectively.The result from producing PVDF/PMMA diaphragms shows that with enough strength and fiber structure can be obtained by blending PMMA and subsequent hot-press treatment at 120 °C. When the ratio of PVDF/PMMA is 8:2, the thermal stability of PVDF/PMMA diaphragms is the best and the micro pores of diaphragm were closed at about 163 °C. The structure of this diaphragm is stable at below 375 °C and its energy storage modulus and loss modulus remain unchanged at less than110 °C. The tensile strength of PVDF/PMMA diaphragms was improved by blending PMMA, and its maximum strength, porosity and aspiration rate are 3440 KPa, 66.7 %and 632 %, repectivly. Electrochemical stability window, ionic conductivity and discharge capacity of PVDF/PMMA(8:2) diaphragms are higher than those of PP, inwhich the ionic conductivity of PVDF/PMMA(8:2) diaphrag s was 2.12×10-3, which is 16 times more than PP. Especially, the discharge capacity of of PVDF/PMMA(8:2)diaphragms substantially does not decrease and coulombic efficiency still remains at about 97 % after 400 cycles.The result from producing PVDF/PMMA/BM diaphragms shows that BM addition is beneficial to the improvement of dimension stability, tensile strength and electrochemical window of the composite diaphragm. With the addition of BM,PVDF/PMMA/BM diaphragms can be used normally at below145? and the tensile strength of 6810 KPa with 0.02 wt. % addition is nearly 5 times than that of PVDF/PMMA. The tensile strength is 5.5 V with 0.01 wt. % addition. The BM addition can reduces the ionic conductivity of the composite diaphragm and the value is 1.73×10-3 with 0.01 wt. % addition, but the conductivity is still better than that of PP. The specific capacity of PVDF/PMMA/BM diaphragm is almost equal to that of PVDF/PMMA when circulation rate is low, but the stability and reversibility of PVDF/PMMA/BM diaphragm are better at high circulation rate.