Electrospun Poly(Vinylidene Fluoride)/Poly(Methyl Methacrylate)/Cellulose Acetate Nanofiber Membrane Separators For Re-Chargeable Liquid Electrolyte Li-ion Batteries

Optimum electrospinning conditions for PVDF membranes was first done.This was carried out by verifying the solution concentrations 10wr%,12wt%,14wt%and 16wt%while varying the electrospinning voltage between 14kV,16kV and 18kV and the spinning distance varied between 16cm,20cm and 22cm.The electrospinning rate of 0.8ml/h,solvent mixture acetone:DMAc ratio at 3:7 and atmospheric conditions were kept constant.The surface morphology was analyzed using the SEM to determine the nanofiber diameter distribution and average.It was deduced that uniform fiber production and distribution was at a solution concentration of 12wt%,electrospinning voltage of 16kV at a spinning distance of 20cm.These spinning conditions were then used for this research.With the optimized conditions,blended polymer membranes were then electrospun at PVDF:PMMA ratios of 100:0,90:10,85:15 and 80:20.Characterization tests were analyzed and discussed.It was found out that addition of PMMA led to increase of absorption properties,pore size,mechanical properties and average nanofiber diameter.It was also observed that addition of PMMA led to a decrease in the contact angle to 100°,melting temperature to 159.7?(80/20 PVDF/PMMA)and crystallinity%to 30.93%(80/20 PVDF/PMMA).These observations were due to the amorphous nature of PMMA and also due to its big side group CH3OCO-.To electrospin CA based membrane,optimizing the mixing solvent was paramount.This was because there were literature proving that with certain ratios of acetone:DMAc,CA was not possible to electrospin.Therefore acetone:DMAc ratios were varied as 7:3 and 3:7.The two ratios were used to mix and electrospin PVDF:PMMA:CA ratios of 90:0:10 and 90:5:5 respectively.Characterization tests were analyzed and discussed.It was observed that to electrospin relatively uniform nanofiber diameters with better distribution,acetone:DMAc at a ratio of 3:7 was to be used.With the verified optimum conditions,blended polymer membranes were electrospun at PVDF:PMMA:CA ratios of 100:0:0,90:10:0,90:5:5 and 90:0:10.These membranes were then tested for various properties and later analyzed.It was found out that addition of CA to the electrospun blended membrane brought about further increase in the porosity absorption%of 99%at 90/0/10 PVDF/PMMA/CA.It was then concluded that addition of PMMA to PVDF improved the wettability and absorption but the fiber membrane could not retain these absorbed liquids due to an increase in pore size.Lack of good retention led to less storage of the liquid electrolyte thus less lithium ions were stored in the membrane.This led to an increase in membrane resistance causing a reduction in ionic conductivity.To improve the retention capability of the membrane,CA was introduced.Addition of CA led to an observed increase in absorption and retention of the liquids.However due to the cellulose based derivatives,there was a reduction in the ionic conductivity.With the attempt to improve the PVDF properties by addition of PMMA and CA,membrane ionic properties were compromised.