Dear @kirk thank you very much for answering the questions! The Team working on the LCA could already start modelling the electrolyte and the current separator. Due to time restrictions (their final assignment is due for early February), the group has come to the following assumptions/decisions for the remaining questions. If you find the time to have a read and provide feedback, it would be great to be able to represent the environmental impact of your electrolyte and separator. The following decisions and assumptions have been considered:
Elektrolyte:
The group noticed that two slightly different electrolyte compositions are mentioned.
The mass-based recipe corresponds to roughly ~2 M KI, ~1 M ZnCl₂, and ~2 M NH₄Cl and also includes triethylene glycol (TEG) as an additive. This composition is also mentioned on the Chemisting post, showing EE = 77.61% (at least for the ninth cycle) compared to the results you linked above (E = 64%).
The other description (the one you referred to early on) specifies 4 M KI, 2 M ZnCl₂, and 1 M NH₄Cl in deionized water, with a total of 10 mL split between the anolyte and catholyte, and does not mention TEG.
The group will assume the TEG composition as the latest version to be implemented on the larger cell format.
Furthermore, the electrolyte volume for the large cell application is still missing. To close this gap, the group wants to scale the volume through the cell area factor (175/2) to maintain the conditions from which EE and other values have been taken. They assume an 880 ml volume for one single cell. Do you estimate this volume to maintain the obtained results until now? Is this the volume foreseen to achieve the 22 Wh/single large-format cell?
Energy loss/demand to store 1Wh
When modelling the use phase, the group considers material or energy inputs necessary to run the flow battery (only related to the defined scope: electrolyte + separator). In the case of the electrolyte, energy loss per storage unit needs to be modelled. The group is assuming the EE value to estimate this. This value does not include energy demand from pumps and electronics, correct? Although the mentioned results represent the performance of the electrolyte without TEG, this EE (64%) value will be assumed to model more conservatively. Meaning: to store 1 Wh, 1.56 Wh needs to be taken from the grid (excluding electronics and pumps). Does this make sense, or are we oversimplifying here?
Used electricity
For the same purpose of modelling the use phase, it is important to define from which country and what type of energy/electricity is being used to charge the electrolyte. Since the users of the FBRC battery can be anywhere, but are currently mostly centered in Europe, the group has decided to choose the European electricity grid mix data to represent the current FBRC reality.
Separator
We would like integrate the environmental impact of the current separator within the efficiency of the large cell format. This means defining a functional unit, for instance: environmental impact per 1 kWh along a defined time unit. Meaning that all the environmental impact generated in a defined period of time (usually defined after the lifespan of a key component, for example the electrolyte) are calculated and then divided through all the energy (for example kWh) which was able to be stored and delivered. Charge/discharge cycles are to be defined (for instance 1 charge/discharge cycle per day, depending on the implementation and cycle duration) to estimate how much energy was stored and calculate all the peripheral environmental impacts. The separator, for instance, would be one of these peripheral impacts, since it would need to be replaced after some cycles (probably faster than the electrolyte). Since cycle durability of photo paper is still unknown, the group will model different scenarios from 10–100 cycles in steps of 30 cycles. Do you feel this is a reasonable range? Do you already now conditions such as density and flow rate the larger cell will work with? The group will assume 4 layers for the larger cell although in some parts are 3 layers stated.
Production and transport of chemicals and separator
The current BOM and building instructions do not provide specific links to purchase the necessary chemicals. To model the electrolyte production, including the transportation of each chemical, the group has assumed the following production locations based on market data and worldwide production trends. If your own experience differs in this, please do not hesitate to comment.
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Ammonium chloride: Production in China. Only global processes are available for production, but transportation will be modelled from China to Europe.
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Deionised water: Local (in our case Europe or Germany as an approximation).
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Zinc chloride: Production in China. Available processes for production will be used, but transportation will be modelled from China to Europe.
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TEG: Production in China. Only global processes are available for production, but transportation will be modelled from China to Europe.
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Separator: China
I hope this update also makes sense for you. We are very much excited to have a first environmental assessment of the electrolyte and separator. This could help monitor the environmental impact of further decisions on those aspects.
Kind regards and hoping to hear from you soon,
Santiago