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I'm hoping with this thread to pin down actual function of lithium hydroxide in an NiFe cell, and expose some of the rationale for the amount added and it's cost effectiveness.
I welcome comments with citation over uninformed (however assertive and determined) opinions based on heresay or unscientific assumptions that the value of this thread remain useful for others.
I have more questions then answers myself, and mods permitting will link out to reference that *should* have weight of experience.
It seems globally recognized that LiOH readily absorbs C02, my research so far has suggested that is the primary reason for adding it in solution to a NiFe battery.
Lithium's higher electronegativity then Potassium results in a LiC03. (2LiOH + CO2 → Li2CO3 + H2O) rather then Potassium Carbonate. KOH + CO2 → KHCO3
ref: http://en.wikipedia.org/wiki/Lithium_hydroxide
Based on my limited experience with batch sheets and availability/cost/purity of KOH flake:
I would suggest that the reasoning behind LiOH increasing the efficiency of ANY NiFe cell is primarily due to the purification of the "brand new" KOH flake which had impurities and KHCO3 to begin with. Given the batch I was provided, significant LiOH would be require simply to bring the KOH solution to a pure "no inherent carbonates" state.
The chemistry of it however similar to that of a NiCad - suggests it is intended instead to preserve the Nickel (pos) electrode.
ref: http://www.cadmium.org/pg_n.php?id_menu=14
I see no reference to this reasoning elsewhere, but invite a reference if someone can offer one.
The costs (referenced in batch sheet reference thread above) surely determine why even new NiFe batteries are shipped with LiOH as the purer forms of KOH and/or LiOH are excessively expensive. My KOH flake had (up to) .44% KHCO3 and sourced LIOH had (up to) 2% Li2CO3 in raw form.
Given LiOH absorbs C02 and locks it up in a strong bond, why not simply schedule additional LiOH addition rather then replace electrolyte?
Is there another reason to have LiOH in the electrolyte mix other then Carbonate absorption?
Maybe:
Improved heat transfer retarding HHO generation?
LIOH acting in conjunction with KOH in Ni/Fe ion exchange?
While some have suggested that graphing charge temperatures may be useful, they make no mention of source KOH batching purities and LiOH purities from the start.
This could explain the wide variation in charging efficiencies touted by manufacturers and why many see NiFe as a lesser storage method.
In a perfect world one might plan their electrolyte mix based on:
1) KOH flake purity
2) LiOH purity
3) operating environment temperature (affecting KOH% required in solution ...- can find no reference to LIOH variation based on temp)
ref: page 3 - http://ironedison.com/images/product...s%20Manual.pdf
While I expect this to be a request for the holy grail, I invite anyone who can speak to these variables in a recorded referenced way.
Again, opinions are great but data is easier to trust, please provide citation with your truths.
Discuss...
I welcome comments with citation over uninformed (however assertive and determined) opinions based on heresay or unscientific assumptions that the value of this thread remain useful for others.
I have more questions then answers myself, and mods permitting will link out to reference that *should* have weight of experience.
It seems globally recognized that LiOH readily absorbs C02, my research so far has suggested that is the primary reason for adding it in solution to a NiFe battery.
Lithium's higher electronegativity then Potassium results in a LiC03. (2LiOH + CO2 → Li2CO3 + H2O) rather then Potassium Carbonate. KOH + CO2 → KHCO3
ref: http://en.wikipedia.org/wiki/Lithium_hydroxide
Based on my limited experience with batch sheets and availability/cost/purity of KOH flake:
I would suggest that the reasoning behind LiOH increasing the efficiency of ANY NiFe cell is primarily due to the purification of the "brand new" KOH flake which had impurities and KHCO3 to begin with. Given the batch I was provided, significant LiOH would be require simply to bring the KOH solution to a pure "no inherent carbonates" state.
The chemistry of it however similar to that of a NiCad - suggests it is intended instead to preserve the Nickel (pos) electrode.
ref: http://www.cadmium.org/pg_n.php?id_menu=14
I see no reference to this reasoning elsewhere, but invite a reference if someone can offer one.
The costs (referenced in batch sheet reference thread above) surely determine why even new NiFe batteries are shipped with LiOH as the purer forms of KOH and/or LiOH are excessively expensive. My KOH flake had (up to) .44% KHCO3 and sourced LIOH had (up to) 2% Li2CO3 in raw form.
Given LiOH absorbs C02 and locks it up in a strong bond, why not simply schedule additional LiOH addition rather then replace electrolyte?
Is there another reason to have LiOH in the electrolyte mix other then Carbonate absorption?
Maybe:
Improved heat transfer retarding HHO generation?
LIOH acting in conjunction with KOH in Ni/Fe ion exchange?
While some have suggested that graphing charge temperatures may be useful, they make no mention of source KOH batching purities and LiOH purities from the start.
This could explain the wide variation in charging efficiencies touted by manufacturers and why many see NiFe as a lesser storage method.
In a perfect world one might plan their electrolyte mix based on:
1) KOH flake purity
2) LiOH purity
3) operating environment temperature (affecting KOH% required in solution ...- can find no reference to LIOH variation based on temp)
ref: page 3 - http://ironedison.com/images/product...s%20Manual.pdf
While I expect this to be a request for the holy grail, I invite anyone who can speak to these variables in a recorded referenced way.
Again, opinions are great but data is easier to trust, please provide citation with your truths.
Discuss...
Comment