Symposium Presentation

PVDF Gel ElectrolytesGelation and Crystallisation investigationsRAID KH. SALMANSchool of Physics and Astronomy/ Soft Matter Group/ University of Leeds/ UKNow At University of Anbar/ College of Education for Pure Sciences/Physics Department/ IraqDr.raid1978@hotmail.com

What are PGEs?Novel materials used in:Rechargeable batteries of laptops, mobile phones, electrical cars etc.LCDs display devicesSecurity tags andSmart cardsFuel CellsSuper capacitors and sensors

Gel Preparation

Cooling from high Temps.Mixing at RTMixing at Elevated Temps.PGEs Preparation

Melting The GelThermoreversible Gelation

Self-packaging (no need for rigid case)

Advantages

Safe and robust (no free liquid to leak).

Copper foil current collectorPolymer gel electrolyteCarbon anodeLithiated metal oxide cathodeAluminium foil current collector

40 mm 0.3 mm

High flexibility and thermo-mechanical stability promoted design creativityNo need for electrodes separators (since the polymer can be used as separator).Easy or one step making

Why studying PGEs?To fill in the gap in knowledge of gelation behaviour in the PGEs in the presence of the electrolyte salt.Understanding ionic conduction behaviour with variation of components qualities and amounts.Find the way to combine ionic conduction with thermo-mechanical stability.Optimise the quality and quantity of solvent and salt.And hence, enhancing rechargeable batteries performance. Increasing safety levels in high energy-density battery productions.

Aims of current studyInvestigation of effect of gel composition on thermo-mechanical properties and ionic conductivity.

Investigation of gelation mechanisms and effect on gel properties

Thermo-mechanical Properties

Thermo-mechanical PropertiesParallel plate method

Thermo-mechanical Properties

Thermo-mechanical PropertiesScrew-Thread method

Mechanical PropertiesPVDF-gel electrolytes showed thermo reversible gelation behaviour

Tsoft is obtained when the modulus drop to 0.1 of its value at room temperature GRT (i.e. G=0.1GRT)

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Thermodynamics Properties

PVDF-gel electrolytes showed melting-crystallisation conservative behaviour

HeatingCoolingMelting PeakCrystallisation peakThermodynamics Properties

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What affects Tm and Tsoft?Tm is highly affected by polymer concentration, either in salted and in unsalted gels.

What affects Tm and Tsoft?DEC addition also causes increase in Tm .

Salt addition also incorporate with Tm increasing.What affects Tm and Tsoft?

How Polymer and solvent quality affects Tsoft and Tm?Hansen Solubility parameters and F-H theory can answer the question.

H.S.PValueUnitPVDF23.226061/Mpa^1/2PC27.21781/Mpa^1/2DEC17.954941/Mpa^1/2EC28.651351/Mpa^1/2

How Polymer and solvent quality affects Tsoft and Tm?Thermodynamics of mixing depends highly on solvent quality as well as polymer concentration

F-H interaction parameter (solvent-Polymer) depends on solvent quality as wellHow Polymer and solvent quality affects Tsoft and Tm?

Ionic conductivity

Ionic conductivity Vs. Polymer concentration

Conductivity Cell

Polymer addition reduces the ionic conductivity

Ionic conductivity Vs. Solvent quality

The low viscosity of the poor solvent (DEC) compete the high dielectric constant of the good solvent (PC).

Ionic conductivity Vs. Salt concentration

Salt concentration enhances ionic conductivity up to 0.8M.

Excessing 0.8M either increase viscosity (i.e. reduce ions mobility).Or causes ions reassociation (reduce the free ions)

ConclusionThemomechanical effect Versus Ionic conductivity

Conclusion

Although polymer concentration increase crystallinity but it highly deteriorate ionic conductivity (tortuosity Vs. Molecular weight)

Conclusion

Solvent quality balances both ionic conduction and melting behaviour (low viscosity Vs. high interaction parameter

Conclusion

Salt concentration play a major role in developing crystallinity and ionic conductivity (nucleation growth enhancement Vs., free ions providing).

Excessing the salt above 0.8M may reverse the action to ionic conductivity due to viscosity increase and/or Li+-BF4- pair re-association.

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Gelation MechanismIsothermal Gelation

tgel

Gelation MechanismIsothermal Crystallisation

Gelation Behaviour

Salted gel in general gels before unsalted

Salted gel gels at higher temperatures than in unsalted

Time of gelation increases withthe increase inTiso

Crystallisation Behaviour

Salted gel in general crystallisebefore unsalted

Salted gel crystallise at higher temperatures than in unsalted

Time of crystallisationincreases withthe increase in Tiso

Crystallisation Vs. GelationAt low temps. Crystallisation occurs before gelationBut at high profile temps. Gelation maintain the system whereas no crystallisation is found.

Conclusion of Gelation mechanismGelation Vs. Crystallisation

Conclusion of Gelation mechanismTwo distinctive temps., profiles can be recognise either in salted and unsalted gels; Low temp., profile, in which, crystals form very quickly followed by instantaneously gelation.High temp., profile, in which gelation maintain the process where is no crystallisation activities can be recognised.Salt addition significantly reduces either gelation and crystallisation time.