| Lithium-ion battery is a kind of green energy power with advantages of high energy density, long recycle life and ability to charge and discharge rapidly. With the improvement of manufacture process, price of lithium battery keeps going down. Lithium-ion battery separator is a key component used for preventing the physical contact of cathode and anode with the ability to allow the migration of ions.Seperator with good properties can play a important role in affecting the battery performance.Electrospinning is an easy and effective way to manufacture nano scale materials, it can provide membrane with fibers of nano diameter, high specific surface area, high porosity, high uptake of electrolyte and so on. Electrospun membrane has much protential to apply as lithum-ion battery separator.Poly(vinylidene fluoride) can be easily electrospun into membrane and has good memchanical properties and crystal structures. Polymethyl methacrylate is a kind of amorphous polymer with good affinity to electrolyte and relatively low cost.In order to combine the advantages of PVDF and PMMA, three ways were adopted which were blending electrospun, core-shell structure manufacture and laminating, also heat treatment was introduce to modify the PVDF/PMMA blending electrospun membrane.Firstly, PVDF/PMMA blending membranes were electrospun and their fiber morphology was observed by SEM (scanning electron microscopy). The influential factors of PVDF/PMMA blending membrane in electrospinning were systematically studied. The results showed that the optimum parameters of PVDF/PMMA blending membrane was as follows; solvent was a mixed solvent of DMAc (N,N-Dimethylacetamide) and acetone (6/4by volume), solutions concentration was12wt%, applied voltage was16KV, the distance between the needle tip and collector was22cm, and electrospinning rate was0.8ml/h, the ratio of PVDF and PMMA was90:10.Secondly, heat treatment was introduced to modify the PVDF/PMMA blending membrane. Respectively,150℃,155℃and160℃were adopted to treat the membranes for2h. The properties of the PVDF/PMMA blending membrane before and after the heat treatment were comprehensively studied. The results showed that heat treatment could improve the uniformty of the membrane, increase the fiber diameter, reduce the hole diameter and porosity and increase the crystallinity. Membranes treated under155℃had the highest crystallinity. Also, heat treatment could improve the mechanical properties significantly. Compared with untreat membranes, tensile strength of membranes treated under155℃enhanced48%. Besides, heat treated membranes had good electrochemical properties and good battery performance.Thirdly, core/shell structured fibers of PVDF/PMMA were prepared by coaxial electrospinning, PVDF was employed as the core material and PMMA was used as the cladding material for PVDF. The properties of membranes consisted of core/shell structure fiber were systematically studied. The results showed that core/shell fibers gave the membrane very high electrolyte uptake (558%) and very good ionic conductivity (3.07×10-3S/cm). Also, the core/shell membranes had similar mechanical properties with PVDF/PMMA blending membranes and the battery tests indicated that core/shell type had high first charge and discharge capacity (157.1mAh/g) and worthy cycle performance.Lastly, PVDF/PMMA/PVDF laminating membranes were prepared through electrospinning and laminating method.The manufacture process was studied and optimized. The properties of laminating membranes were generally studied. The results told that PVDF/PMMA/PVDF laminating membranes had smaller hole diameter but relatively high porosity. The mechanical properties of laminating membranes were relatively low, the breaking extension was less than60%. Besides, PVDF/PMMA/PVDF laminating membranes had reasonable good electrochemical properties better than the untreated blending membrane except for the cycle performance, the capacity of laminating membranes decreased6.3%after50cycles. |
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