My adventures building a DIY Mn/Fe flow battery

Patrik L said:

I'm gonna address a few things in this one post, its simpler that way.

1)

1. If we look at a 48V@10kWh Li-ion battery pack from LG Chem, then 7500€ is a fair price. Here we can expect roughly 3-5k cycles.
2. If we then look at similar LFP battery pack, then we land between 5500-7500€ but get substantially longer cycle life. LFP's are estimated to return 5000-10,000 cycles.
3. A 10kWh NiFe pack on the other hand will cost roughly 10,000€, but there, >10,000 cycles is no issue.
4. An all iron salt battery, the FeCl, is estimated to do more than 20,000 as in little to no losses are seen at those cycling's - but I currently do not have a cost projection here. So lets use NiFe levels.

Point being, if we consider the battery's above, then the MnFe has to be able to compete and its here that, at least I, is fumbling in the dark. I have no cyclability reference besides little to no degradation at 500 cycles. So before one worry about the cost for hundreds of kg, I would want the base knowledge to be known

2). Stumbled upon a paper where they used an anion-exchange membrane in a FeCl battery at pH of 2-3 (Tokuyama A901, 11 μm thickness) which was stable for at least 50 cycles.

Ttitle: ... A High Efficiency Iron-Chloride Redox Flow Battery for Large-Scale Energy Storage - DOI 10.1149/2.0161601jes ... curious about your thoughts here.

and here is a PDF with reference to the membrane: https://www1.eere.energy.gov/hydrogenandfuelcells/pdfs/amfc_050811_fukuta.pdf

also some info here http://www.astom-corp.jp/en/product/02.html

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ASTOM & Tokuyama merger information: http://www.membrane-guide.com/membrane_separation/ion-exchange/japan_ion_exchange_membrane.htm

3) The colour shifts sounds mesmerising

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An important point is that both NiFe and FeCl3 flow batteries are very maintenance heavy.

I don't know if you have used NiFe batteries before, but periodic electrolyte changes - which involves moving and dumping large amounts of highly concentrated KOH+LiOH solutions - need to be done, often several times per year. This is especially true for some of the modern chinese versions of NiFe batteries, which are constructed much more cheaply than those that Edison made early on. While NiFe might sound great in some aspects, in practice it is a quite annoying battery chemistry to run and maintain. I have run these batteries before and I would say they are anything but care-free.

In the case of FeCl3 flow batteries, a similar problem happens. Due to the H2 evolution at the anode, you will need to constantly adjust the pH of the anolyte so that you don't start seeing hydroxide precipitation issues. These pH adjustments would need to be done practically every 50 or so cycles of the battery. Thankfully this process is much more prone to automation, given that you just need to keep the pH at a low value.

Using an anion exchange membrane would be ideal, but considerably more expensive than the commonly used cation exchange membrane types. Conductivity of anions is also slower than protons, so this means you also get a penalty in terms of current density.

Another issue is that since you're plating a metal, your capacity does not scale solely with the volume of electrolyte but you also need to increase the physical volume of the anodes to get more capacity. This imo, is counter productive since the ideal of a flow battery is to fully decouple power density and energy density of the setup.

danielfp248 said:

An important point is that both NiFe and FeCl3 flow batteries are very maintenance heavy.

I don't know if you have used NiFe batteries before, but periodic electrolyte changes - which involves moving and dumping large amounts of highly concentrated KOH+LiOH solutions - need to be done, often several times per year. This is especially true for some of the modern chinese versions of NiFe batteries, which are constructed much more cheaply than those that Edison made early on. While NiFe might sound great in some aspects, in practice it is a quite annoying battery chemistry to run and maintain. I have run these batteries before and I would say they are anything but care-free.

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But the salts are non consumable, the only consumption is water due to hydrogen evolution or evaporation. That one has to replace the entire electrolyte on the NiFe that often is new to me... honestly, that is brand new info. In some cases when the battery has been sitting for a long time (many years), replenishing the electrolyte is required.

For clarification and resolution: Why exactly the high (NiFe) electrolyte replacement frequency ?

danielfp248 said:

In the case of FeCl3 flow batteries, a similar problem happens. Due to the H2 evolution at the anode, you will need to constantly adjust the pH of the anolyte so that you don't start seeing hydroxide precipitation issues. These pH adjustments would need to be done practically every 50 or so cycles of the battery. Thankfully this process is much more prone to automation, given that you just need to keep the pH at a low value.

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I was about to say that adjusting the pH due to water losses isn't very complicated and indeed, an automatic filling system can be used - some good news ... LOL. One can go one step further and use a "gas filter" section, an adaptation of the AGM battery, which uses nonwoven poly-propylene (PP) fabric separator to slow down the motion of the gas or trap the gas for long enough such that H2 and O2 species have enough time to recombine. PP is inert to many chemicals and these types of fabrics can be found via geotextile as an example and is dirt cheap.

So outgassing is the least of ones problem I would say. A redundant system with pH monitoring, "gas filter" and ventilation can relatively easy be set up.

I was actually going to experiment with a NiFe PP pouch cell battery as a means to produce a dirt cheap NiFe battery, but ran into the nickel salt problems.

danielfp248 said:

Using an anion exchange membrane would be ideal, but considerably more expensive than the commonly used cation exchange membrane types. Conductivity of anions is also slower than protons, so this means you also get a penalty in terms of current density.

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Right... well, lets say outgassing is minimized (see above), then a cation membrane would be fine, even the lower roundtrip efficiency.

danielfp248 said:

Another issue is that since you're plating a metal, your capacity does not scale solely with the volume of electrolyte but you also need to increase the physical volume of the anodes to get more capacity. This imo, is counter productive since the ideal of a flow battery is to fully decouple power density and energy density of the setup.

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I thought that was the case for any battery. As in; 1 cm^2 have X mA that it can support. For flow battery we need to account for the electrolyte's ability to give or take a charge which is connected to the interaction of the electrolyte and current collector and the size of the current collector. So the lower the values are in terms of current and/or current needs, the larger the area has to be.

Are you saying there is an advantage to the non plating MnFe cell where since you are not plating, picking up or giving off a charge is easier and therefor you are not bound to current density in the form of area alone, but its more of an area and flow combination ? .... (man oh man do I wish I was properly trained as a chemist such that I could explain things properly... LOL)

Patrik L said:

For clarification and resolution: Why exactly the high (NiFe) electrolyte replacement frequency ?

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About why a change of the electrolyte in NiFe cells is needed with a higher frequency, the answer is that the KOH/LiOH electrolyte is unstable to CO2 in the atmosphere, so it captures CO2 very efficiently as a function of time. This CO2 lowers the conductivity and the carbonates formed allow for the formation of Ni and Fe carbonates which are not active in the battery and cause the battery to actually lose capacity as a function of time. Since the batteries cannot be sealed due to their production of H2, they are exposed to CO2 and gradually become poisoned.

In my practical experience with modern NiFe batteries, this process can happen relatively quickly. Fast enough so that you need to perform this change once per year.

This is one of the problems with any rechargeable high pH battery technology that is not airtight. The formation of carbonates kills the battery with time.

Are you saying there is an advantage to the non plating MnFe cell where since you are not plating, picking up or giving off a charge is easier and therefor you are not bound to current density in the form of area alone, but its more of an area and flow combination ? .... (man oh man do I wish I was properly trained as a chemist such that I could explain things properly... LOL)

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With a flow battery, the idea is that your cathode/anode are completely neutral (don't participate in the reaction) so all they do is provide you with surface area for the electrochemistry. This means that if you need more power - to produce more watts - all you need is to add more electrode surface area (more stacks). This can help you increase your voltage and current to whichever levels you require.

However, if you want more capacity (more kWh) but you don't need more power output, all you need is to add more tank volume. Since capacity depends only on the electrolyte volume.

The above is true for any RFB that does not plate anything on the electrodes. Such as Vanadium RFB.

When you plate something on the electrodes, the area of your electrodes also becomes tied into your capacity, since you need to deposit metal onto those electrodes and the mass you can put in those electrodes depends on their volume and active area. It is then not enough to just increase your tank volumes to increase capacity, you also need to increase your electrode area. This negates a big advantage of the classic RFB which is that you can endlessly expand capacity just by getting bigger tanks.

When I started my battery journey, I had no idea what it would involved or what the end station is. Both the former and later is evolving as we speak, which I am very... very happy for, and this is the entire reason for me being such involved... that and the prosperity for building myself and saving some bucks .. LOL.

I had no idea oxygen or carbon-dioxide was such a crucial part for the degradation of the NiFe battery operation. I guess it makes sense if one start looking at the chemistry or get the "aha" moment, like you provide me with now. I am starting to understand why Encell Technology Inc stopped production of their flooded NiFe battery in favour for a sealed and service free variant and I am grateful I am aware of the oxygen issues for battery's in general.

So we are fundamentally talking about two types of RFB: Plating and non-plating variants and you want to work on non-plating aka a Vanadium Redox replacement chemistry. Kewl. Come to think of it, this was mentioned early on in your blog... duh... he he

I also got a price quote for the Yara chelate products. The Mn variant is 14,82€/kg and the Fe variant is 18€/kg (incl. VAT). I guess that can be viewed as premium price, on the other hand, I would say I trust Yara more than a Chinese vendor. Some delivery's and purity of the products is questionable according to some who order from China, Alibaba etc . But lets see what happens. No matter, I will work with smaller quantity's to start with.

Q: Proper cycle tests has to be done on the open source flow cell you are planning to build later this year ?

So what are you doing now, just monitoring crossover in a static environment ?

Patrik L said:

Q: Proper cycle tests has to be done on the open source flow cell you are planning to build later this year ?

So what are you doing now, just monitoring crossover in a static environment ?

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Yes, cycling can only be done on a proper flow cell. At the current densities I can sustain without side reactions - due to the low surface area of my electrodes and the big space between them - I need like 1 week per cycle of a quite dilute solution (50mM). So cycling is not gonna happen here.

I am just ensuring the chemistry works - meaning I dont see any iron oxides or manganese oxides precipitate - and the potentials measured are as expected. I can also observe crossover of the Fe-EDDHA and measure pH changes on the discharged and charged states. I can also observe the color changes and just get an overall idea of what changes to expect when cycling a true flow cell.

Got it. Because the two electrolytes are of different metal species, is there a way to recover crossover contamination or does that simply become a permanent loss of potential ? ...

Iron salt have the advantage of being the same on both sides, crossover is not a contamination per say, just loss of potential during that cycle. Which I guess is one of the advantages.

Patrik L said:

Got it. Because the two electrolytes are of different metal species, is there a way to recover crossover contamination or does that simply become a permanent loss of potential ? ...

Iron salt have the advantage of being the same on both sides, crossover is not a contamination per say, just loss of potential during that cycle. Which I guess is one of the advantages.

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In the case of this battery crossover would lead to permanent loss of capacity. It doesn't poison the catholyte/anolyte though, you will just lose some capacity as a function of time. However, the fully intermixed electrolyte is still functional, so you can never lose more than 50% of the capacity in this way. With a decent membrane it should take a decade for you to lose even 1% in this manner though, since the electroactive species are so large.

It doesn't affect potential much though, just capacity.

Sounds promising. The self-discharge is different I will assume since there we are talking about the free motion of cations through the membrane vs capacity loss due to contamination.

Generally speaking: What is an accepted self-discharge level ?

Patrik L said:

Sounds promising. The self-discharge is different I will assume since there we are talking about the free motion of cations through the membrane vs capacity loss due to contamination.

Generally speaking: What is an accepted self-discharge level ?

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These should not self-discharge in the traditional sense, since your storage is put into tanks and the amount that is left within the stack is negligible. The expected self-discharge would be due to reactions of atmospheric oxygen with reduced Fe-EDDHA.

So basically, without active redox, as in an ohmic load discharge, the anolyte and catholyte will hold their state of charge quite well.. and yes, because not all of the electrolyte is present in the cellstack, that which are located in the tanks and if influence of O2 and CO2 is very low, should exhibit good values.

Btw, how does one recover the lytes from dissolved O2/CO2... by means of nitrogen purging like we talked about earlier ?

Patrik L said:

So basically, without active redox, as in an ohmic load discharge, the anolyte and catholyte will hold their state of charge quite well.. and yes, because not all of the electrolyte is present in the cellstack, that which are located in the tanks and if influence of O2 and CO2 is very low, should exhibit good values.

Btw, how does one recover the lytes from dissolved O2/CO2... by means of nitrogen purging like we talked about earlier ?

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The influence of CO2 should be minimal, since at neutral pH it is not taken up in a major way by solutions and no significant amount of carbonates are formed.

Oxygen will react right away with reduced Fe-EDDHA, so any you don't keep out will just discharge your battery. You have to keep it out by keeping the system under N2 positive pressure and having it well sealed, especially the anolyte tank. The catholyte won't react with the air at all.

I am looking forward to starting my own tests under your wings. Clocking performance and endurance is one of the more exciting aspects of battery's besides the chemistry - not that I have ever done that and everything is new. Until then, I'd best let you steer the ship and do the groundwork

When will this end, I have a new question for you ... LOL

In your ion exchange membrane research, did you consider the use of Regenerated Cellulose (MWCO of 6,000–8,000 g mol^-1) ? Bellow is a picture which use regenerated cellulose dialysis membrane as the ion exchange membrane as a more affordable NAFION replacement with aqueous electrolyte and sodium chloride as support salt.

I am only investigating since regenerated cellulose is a commercial available product/film that could (if the right type and price to performance, is located) make the construction of the cells a bit simpler with less steps involved. Mind you, this is not criticism of your membrane work, I very much appreciate that. I ask only to bring clarification.

I will share my source if you want or need it.

- edit -
I wonder if your PVA/Cellulose is too close of a solution as in rendering Regenerated Cellulose mute. We don't exactly need the membrane to be clear/transparent, but I will keep this post present as an alternative.

I had an epiphany and memory yesterday. I've always wanted to have or own a nitrogen selective membrane, but there wasn't a good time for one and then we had all these debates and suddenly there is a need for one :D. I just added: "build a nitrogen gas station" to the list of stuff I will need. While buying a N2 gas-tube might be cheaper atm, I will need a gas station later on anyway so might as well do the investment.

Have a wonderful Saturday.

I like to monitor multiple and parallel projects when I involve myself in something and a parallel project that qualify as parallel is the CMBLu and BALIHT EU project which involves multiple organizations and companies. To put it simple, this is a big project with the focus on organic lignin electrolyte which is far more environmentally friendly and less costly than your traditional vanadium RFB.

BALITH overview: A new generation of organic flow batteries shows promise for energy storage

The EU-funded BALIHT project is designing new redox organic flow batteries that can work at temperatures of up to 80 °C. Researchers claim that the batteries will offer longer duration, higher power and a 20 % higher energy efficiency compared to other organic battery types. The new battery will be based on low-cost, abundant organic molecules that are easily dissolved in water, electrolytes comprising lignin, thin non-fluorinated membranes and carbon electrodes. Redox organic flow batteries are one of the most promising approaches to sustaining a grid powered by the sun and wind, improving grid flexibility and stability and providing high-performance charge points for electric cars.

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CMBLu overview:

The renewable energy transition needs powerful, scalable and affordable energy storage systems that do not harm people and nature. However, current options have been plagued with high cost, safety issues, environmental and social concerns. They are based on scarce resources that are extracted under ethically and ecologically questionable conditions with high energy consumption and transported around the world via long supply chains. Due to the rapidly increasing demand for batteries in the field of electromobility, there are going to be dramatic bottlenecks in the availability of these materials. For numerous applications, the flammability of existing battery systems is another major problem.

CMBlu’s Organic Solid-Flow Battery is different – and it is a first of its kind to be commercialized. Our technology is based on fully recyclable organic materials that are available all over the world. The aqueous electrolytes solutions are non-flammable and ensure an absolutely safe and reliable operation. Compared to previously established battery systems, our Organic Solid-Flow Batteries are characterized by free scalability between power and capacity. They can therefore be adapted precisely to the individual requirements of the respective application with corresponding cost advantages. The system-inherent separation of the electrolyte and the actual energy converter not only avoids self-discharge, but also enables the original performance to be restored by simply replacing individual components instead of the entire battery.

A clean and renewable energy future demands radical new concepts for energy storage. This truly green Organic Solid-Flow Battery disrupts the energy storage market to accelerate the transition and to meet climate goals sooner.

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If you go to some of these project pages you will find that they reference Vanadium RFB as the electrolyte to overtake and that a +30% energy density over Vanadium RFB is achieved which mean that CMBLue organic lignin battery achieves 30 W-h/l - as a reference. This is bellow Lead-Acid 40 W-h/l but above the std Nickel-Iron Alkaline battery at 20-25 W-h/l

If we then look at the definition of what chelate is then Google describe chelate as: "a compound containing a ligand (typically organic) bonded to a central metal atom at two or more points"

Wikipedia describes Ligand as: "In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs, often through Lewis bases. The nature of metal–ligand bonding can range from covalent to ionic."

I searched on Chemisting's blog for the word organic under the Mn/Fe project pages and didn't find organic mentioned, which is a shame since organic flow battery is the trend of long term storage solutions and effectively, if it wasn't clear, Chemisting's Mn/Fe-chelate flow battery is of the organic type.

• Water based​
• Affordable​
• Ultra-Scalable​
• Long-Lasting​
• Recyclable​
• and ... Safe​

Everything that which CMBLu/BALIHT are striving for. I figured this was mention-worthy. While the CMBLu focuses on metal free (aka. Vanadium free) flow battery, they seem to overlook Ligand chemistry or I am sure we would have read bout it. And while lignin (complex organic polymer) is based on plant chemistry and plentiful, so seems to be the case for Mn- and Fe-chelate as well. Meaning no matter, both Lignin and Ligand are organic, plentiful, inherently low toxicity, safe, affordable and non-plating full ionic electrolyte type.


Sources:
1. https://cordis.europa.eu/project/id/875637
2. https://www.cmblu.com/en/technology/
3. https://baliht.eu/objectives/
4. https://en.wikipedia.org/wiki/Lignin
5. https://en.wikipedia.org/wiki/Ligand

Patrik L said:

I like to monitor multiple and parallel projects when I involve myself in something and a parallel project that qualify as parallel is the CMBLu and BALIHT EU project which involves multiple organizations and companies. To put it simple, this is a big project with the focus on organic lignin electrolyte which is far more environmentally friendly and less costly than your traditional vanadium RFB.





If you go to some of these project pages you will find that they reference Vanadium RFB as the electrolyte to overtake and that a +30% energy density over Vanadium RFB is achieved which mean that CMBLue organic lignin battery achieves 30 W-h/l - as a reference. This is bellow Lead-Acid 40 W-h/l but above the std Nickel-Iron Alkaline battery at 20-25 W-h/l

If we then look at the definition of what chelate is then Google describe chelate as: "a compound containing a ligand (typically organic) bonded to a central metal atom at two or more points"

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Wikipedia describes Ligand as: "In coordination chemistry, a ligand is an ion or molecule (functional group) that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's electron pairs, often through Lewis bases. The nature of metal–ligand bonding can range from covalent to ionic."

I searched on Chemisting's blog for the word organic under the Mn/Fe project pages and didn't find organic mentioned, which is a shame since organic flow battery is the trend of long term storage solutions and effectively, if it wasn't clear, Chemisting's Mn/Fe-chelate flow battery is of the organic type.

• Water based​
• Affordable​
• Ultra-Scalable​
• Long-Lasting​
• Recyclable​
• and ... Safe​

Everything that which CMBLu/BALIHT are striving for. I figured this was mention-worthy. While the CMBLu focuses on metal free (aka. Vanadium free) flow battery, they seem to overlook Ligand chemistry or I am sure we would have read bout it. And while lignin (complex organic polymer) is based on plant chemistry and plentiful, so seems to be the case for Mn- and Fe-chelate as well. Meaning no matter, both Lignin and Ligand are organic, plentiful, inherently low toxicity, safe, affordable and non-plating full ionic electrolyte type.

​

Sources:
1. https://cordis.europa.eu/project/id/875637
2. https://www.cmblu.com/en/technology/
3. https://baliht.eu/objectives/
4. https://en.wikipedia.org/wiki/Lignin
5. https://en.wikipedia.org/wiki/Ligand

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Bear in mind that an "organic" RBF is not a battery that contains an organic molecule but a battery where the redox chemistry happens in the orbitals of an organic molecule. Meaning the organic molecule is actively involved in the redox process. In the case of an Mn-EDTA/Fe-EDDHA battery, the redox process happens at metallic centers, even if organic molecules are wrapped around these centers, they are not the main part of the electrochemical process. Such a battery would be considered inorganic, in the same group as a Vanadium RFB. So long story short, the flow battery I propose is not of the organic type.

danielfp248 said:

So long story short, the flow battery I propose is not of the organic type.

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I see and thanks for the correction. I feel like removing that entry but will let it remain since its a good way to distinguish the organic and inorganic flow battery, just like plating vs non-plating.

And If my many posts and "aggressive" participation in this thread is offensive, let me know and I will tone it down. I certainly don't intend to hijack it or lead it astray.

Patrik L said:

I see and thanks for the correction. I feel like removing that entry but will let it remain since its a good way to distinguish the organic and inorganic flow battery, just like plating vs non-plating.

And If my many posts and "aggressive" participation in this thread is offensive, let me know and I will tone it down. I certainly don't intend to hijack it or lead it astray.

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No problem, very happy to have you here. I'm not posting that much right now (busy with work!) but keep posting!

I am very happy to be here and learn the ins and outs of battery's. Now that many of my questions have been answer, my entry's will slow down a bit and wait for more updates from you, but I do have a question for you non the less.

How come you "stumbled upon" Ligand or the Mn- and Fe-chelate and decided to experiment with it and not Lignin (Lignosulfonate). Do you see advantages and disadvantages (for both) that eludes others ?