Performance And Preparation Of Electrospun PVC Modifying Membranes For Lithium Ion Battery

Recently, polymer lithium-ion batteries prepared with polymer electrolytes （PEs）have drawn the general attention of many researchers. The PEs have severaladvantages over the traditional liquid electrolyte. These advantages include such as nointernal shorting, leakage of electrolytes and non-combustible reaction products at theelectrode surface and so on. These advantages of the PEs greatly improved theperformance of polymer lithium-ion batteries. So the PEs become an importantresearch content in polymer lithium-ion batteries.The PEs should possess favorable electrochemical performance and excellentmechanical strength at the same time in their practical application. But until now, thePEs which have good electrochemical performance and mechanical properties are few.The work is started from the good electrochemical performance and mechanicalproperties of the PEs, PVDF、PAN and PMMA which have good electrochemicalperformance are chose as the main matrices, the amorphous PVC with goodmechanical stiffener is blended to modify their performance. The research content ismainly divided into the following three aspects:（1） PVDF was chosen as the main matrix, PVC was added to modify itsperformance through blending. We have made use of electrospinning to preparePVDF/PVC composite fibrous membranes, the characterization and electrochemicalperformances of the electrospun PVDF/PVC fibrous membranes were investigated.The results showed that the appropriate addition of PVC effectively decreased thecrystallinity of PVDF and improved the ionic conductivity. When the quality ratio ofPVDF and PVC was8:2, the PEs had the lower crystallinity、the higher uptake andionic conductivity(2.25×10^-3S cm^-1). The electrochemical stability window of the PEsbased on PVDF/PVC （8:2, w/w） reached5.1V versus Li. Li/LiFePO₄cell based onPVDF/PVC （8:2, w/w） PEs showed a first discharge capacity of145.1mAh g^-1at0.1C-rate and exhibited good cycle performance.（2） PAN was chosen as the main matrix, PVC was added to PAN to modify itsperformance through blending. PAN/PVC composite fibrous membranes wereprepared by electrospinning, the characterization and electrochemical performances ofthe electrospun PAN/PVC composite fibrous membranes were investigated. Theresults showed that the addition of PVC increased the mechanical strength of polymerelectrolyte membrane. Pure PAN-based PEs is jelly which has poor mechanical performance and can not be used to practice. When the PVC with good mechanicalstiffener was added to PAN, the condition of composite PAN/PVC PEs becomesfree-standing. When the quality ratio of PAN and PVC was8:2, the PEs had goodelectrochemical performance and mechanical properties. The ionic conductivity ofPAN/PVC （8:2, w/w） PEs was1.05×10^-3S cm^-1, the electrochemical stability windowreached4.9V versus Li. Interfacial characteristics result showed that PAN/PVC （8:2,w/w） PEs had a good interfacial stabilization with lithium metal anode.（3） PMMA was chosen as the main matrix, PVC was added to PMMA tomodify its performance through blending. PMMA/PVC composite fibrous membraneswere prepared by electrospinning, the characterization and electrochemicalperformances of the electrospun PMMA/PVC composite fibrous membranes wereinvestigated. The results showed that the addition of PVC greatly increased themechanical strength of polymer electrolyte membrane. Pure PMMA electrospunfibrous membrane dissolved in1M LiClO₄-EC/PC when it was activated. The PEsbased on pure PMMA can not be gained. When the PVC with good mechanicalstiffener was added to PMMA, the condition of PMMA/PVC composite PEs becomesfree-standing. The ionic conductivity of PMMA/PVC composite PEs was above10^-3S cm^-1, the electrochemical stability window exceed4.5V versus Li. Interfacialcharacteristics result showed that PMMA/PVC composite PEs had a good interfacialstabilization with lithium metal anode.