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Preparation and Modification of Lithium-ion Battery Membrane/Separator

Javadi, Omid | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 52160 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Soltanieh, Mohammad; Mousavi, Abbas; Fathollahi, Abolfazl
  7. Abstract:
  8. Electrolyte separator is the major component of lithium-ion batteries which the battery safety directly depends on it. In this work, a membrane separator based on the polyvinylidene fluoride (PVdF) was prepared via non-solvent induced phase separation (NIPS) method with water and ethanol as non-solvent and a mixture of dimethylformamide (DMF) and acetone as solvents. The effect of various acetone/DMF ratios and type of non-solvent on the structural, mechanical and electrochemical properties of separator was studied. The separator was characterized by FE-SEM, tensile strength, electrochemical AC-impedance spectroscopy, thermal stability and linear sweep voltammetry (LSV). Additionally, the charge–discharge studies were carried out by fabricating a lithium foil/ polymer electrolyte membrane/ LiFePO4 cell. The results show that with increasing the acetone content in the membrane solution the tensile strength and the thermal stability of the PVdF separator enhances. The introduction of non-solvent ethanol, solvent DMF and polyurethane enhances the porosity and ionic conductivity. The membrane separator sample with non-solvent ethanol, solvent composition of acetone/DMF: 80/20 and PVdF/PU:95/5 blend ratio showed good mechanical strength (7.83 MPa), high porosity (66.3%) and high ionic onductivity(1.18mS/cm) as well as excellent thermal stability. The cycle performance is superior to the PP Celgard separator. For PP Celgard after 60 cycles, a capacity drop of 17% was observed. While the drop in the capacity of the half-cell prepared with the above sample was negligible
  9. Keywords:
  10. Lithium Ion Batteries ; Polymer Membrane ; Polyvinylidene Fluoride (PVDF) ; Phase Inversion

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