Dear all, I am preparing polymer electrolyte membranes using PEG and PEO as my polymer matrices separately and acetonitrile (HPLC grade) as solvent. As pilot practice for casting I only prepared pure polymer mixtures without Li electrolyte salt. For PEO it easily became a gel and I have questions on how to cast them since it has solidified.
Will this phenomenon happen if I add the Li electrolyte salt and ceramic nanofillers? I am following the recipe of this journal: J. Mater. Chem. A, 2015, 3, 10760-10766.
Thank you very much for your inputs and suggestions.
Stephanie, the mechanical property of the dried PEO/PEG membrane is related to the molecular weight of the polymer. Believe your PEO's molar mass is above 3400 g/mol, the entanglement molecular weight of it. Since the addition of salt to PEO matrix alters its mechanical property, I would encourage you to consider not excluding salt during the pilot test. The following protocol is normally what we use to make a linear PEO based electrolyte membrane in lab:
1) stir PEO+acetonitrile (PEO 4wt%) over night.
2) make salt+acetonitrile solution; the weight percentage of the salt depends on its solubility in acetonitrile and you should look up for this value. We prepare lithium (or sodium) triflate in acetonitrile at 3 wt%. For Li or Na - TFSI you can make this value higher. Stir the salt+acetonitrile solution overnight.
3) Mix the two (polymer slurry and salt+acetonitrile solution according to your desired salt concentration in the final membrane) and stir them over another 5~8 hours. At this step you should stir the liquid decently slow to avoid trapping gas bubbles in the slurry.
4) Cast the film in a Teflon evaporating dish. The diameter of it I use is 57 mm. The volume of the polymer slurry I cast into this petri dish is about 7 mL - the final membrane has decent quality. You can control the polymer-salt-acetonitrile quantity to control the thickness of the film.
5) Let it dry over 24 hours at room temperature in the fume hood
6) Put it in vacuum at 50 degree C and dry overnight before transferring it to an argon-filled glove box (ideally you dry the film in the antechamber with temperature control modulus in the same glove box)
You may find the following publication useful
DOI: 10.1021/acsenergylett.8b00680
Stephanie, the mechanical property of the dried PEO/PEG membrane is related to the molecular weight of the polymer. Believe your PEO's molar mass is above 3400 g/mol, the entanglement molecular weight of it. Since the addition of salt to PEO matrix alters its mechanical property, I would encourage you to consider not excluding salt during the pilot test. The following protocol is normally what we use to make a linear PEO based electrolyte membrane in lab:
1) stir PEO+acetonitrile (PEO 4wt%) over night.
2) make salt+acetonitrile solution; the weight percentage of the salt depends on its solubility in acetonitrile and you should look up for this value. We prepare lithium (or sodium) triflate in acetonitrile at 3 wt%. For Li or Na - TFSI you can make this value higher. Stir the salt+acetonitrile solution overnight.
3) Mix the two (polymer slurry and salt+acetonitrile solution according to your desired salt concentration in the final membrane) and stir them over another 5~8 hours. At this step you should stir the liquid decently slow to avoid trapping gas bubbles in the slurry.
4) Cast the film in a Teflon evaporating dish. The diameter of it I use is 57 mm. The volume of the polymer slurry I cast into this petri dish is about 7 mL - the final membrane has decent quality. You can control the polymer-salt-acetonitrile quantity to control the thickness of the film.
5) Let it dry over 24 hours at room temperature in the fume hood
6) Put it in vacuum at 50 degree C and dry overnight before transferring it to an argon-filled glove box (ideally you dry the film in the antechamber with temperature control modulus in the same glove box)
You may find the following publication useful
DOI: 10.1021/acsenergylett.8b00680
Dear Dr Guang Yang, may I ask additional queries?
1) Where would the EO:Li ratio calculations come in in this protocol?
2) The initial solutions I prepared were very much in liquid form and not viscous to be poured into a Teflon plate. Is there a need to apply temperature while stirring the polymer solution?
Thank you very much for your assistance.
a. molecular ratio of an EO repeating unit is about 44g/mol, you can get the total mole of EO, n(EO) by m_PEO/44, as m_PEO the mass of polymer added in your system. mole of salt, n(salt) is _ mass of salt/molecular weight of salt - your mole ratio of EC-SALT = n(EO)/n(salt)
b. let the liquid dry over 24 hours and you will see a white film at the bottom of the evaporating dish
Thank you very much Dr Guang Yang for your very helpful suggestions!
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