Designing an Open-Source Flow Battery Kit

Kirk Smith

Flow Battery Research Collective

Daniel Fernández Pinto

Flow Battery Research Collective

Josh Hauser

Utrecht University/FAIR Battery Project

Sanli Faez

Utrecht University/FAIR Battery Project

April 9, 2024

Flow Battery Research Collective: Who are we?

Researchers who want to help develop and democratize technologies for affordable, sustainable energy storage

https://fbrc.dev

What did we do?

• Built an affordable, complete kit which allows small-scale testing, using:

  • existing open-source tools: FreeCAD software, MYSTAT potentiostat (Irving, Cecil, and Yates 2021)

  • non-proprietary components: paper separators, graphite foil

Why did we do it?

• Commercial test kits are expensive
• Existing academic designs aren’t yet accessible to non-experts: lacking documentation and everything needed to perform experiment
• We want to see for ourselves if these technologies work

Commercial cells

ElectroCell

Price on request, requires machining specialized graphite plate “Electrocell: Micro Flow Cell” (2021)

Electrocell (cont.)

✅ Pros:

• Highly configurable
• Simple sealing principle
• Internal manifolding

❌ Cons:

• Machining of metal and specialized graphite material
• Price

C-Tech Innovation

Price on request ($$$) “C-Tech Innovation: C-Flow 1×1 Electrochemical Cell” (2024)

Pinflow Energy Storage > $ 7,000 USD

Price on request “Lab-Cell by Pinflow” (2024)

Redox-Flow.com > € 2,900

Note the internal manifolding

“Redox-Flow.com: A-Cell, Redox Flow Battery Test Cell” (2024)

MTI Corporation: > $ 9,000 USD

“MTI Intl: Complete Testing Package for Vanadium Redox Flow Battery” (2024)

Scribner > $ 5,000 USD

Price on request, internal manifolding, flow fields

“Scribner: Redox Flow Cell Test Fixture” (2024)

General observations of commercial test cells

• Not cheap

• Pricing not transparent (two exceptions)

• Sturdy: thick metal plates

• Requires machining of metal and graphite plates

• Electronics/pumps not always included

Academic cells

Companies may buy those commercial cells, academic researchers often make their own.

Here are some of their designs.

QUILL cell

• Tested with vanadium chemistry

• Good overview of existing cell designs in Supporting Information

O’Connor et al. (2022)

QUILL cell (cont.)

✅ Pros:

• Open source!
• 3D printable cell design
• Improved performance vs. commercial C-Tech cell
• Cell fabrication and assembly documentation
• Ergonomic, closes with C-clamp
• Minimal graphite machining needed
• Flow enters electrodes in-plane with membrane/electrode¹

❌ Cons:

• Cell design cannot be milled (overhanging geometry)
• Large cell pitch of ~8 mm (distance between current collectors)
• Doesn’t include balance-of-plant
• Couldn’t seal polypropylene cells (only ABS)

1. Important for managing crossover/hydraulic pressure, esp. with porous separators

MIT Cell (Brushett Group)

(Milshtein 2017)

MIT Cell (cont.)

✅ Pros:

• Open-source!
• Well-documented
• Machinable from solid polypropylene
• Capable of small interelectrode distances / cell pitch

❌ Cons:

• Requires milling of specialized graphite plate material
• Flow enters electrode perpendicular to electrode/membrane plane
• Fixed size at ~2 cm²

Southampton Cell

Successful demonstration of 3D-printed cell components, using zinc-cerium chemistry. Similar approach to Electrocell (Arenas, Walsh, and León 2015)

General observations of academic test cells

• Varying degrees of openness/documentation
• Use of additive manufacturing methods common
• Doesn’t include entire, reproducible system

Our design

Exploded view of current design

Exploded view of the current cell design

Affordable membrane

2,520 EUR/m² vs. 6 EUR/m² (Ion Power GmbH and Amazon UK)

Affordable current collectors

1,477 EUR/m² vs. 66 EUR/m² (FuelCellStore and Amazon US)

Our design: pros and cons

✅ Pros:

• Off-the-shelf parts, including graphite foil used on top of copper current collector
• 1 cm² to 10 cm² area configurable
• Possibility for small interelectrode gap
• Flow enters porous electrode in-plane with membrane

❌ Cons:

• In practice, 3D-printable… but machined cell bodies are best
• Precise fit required between copper current collectors and plastic cell body
• Thick plastic required in absence of metal compression plates

Entire kit, front

Jig holds everything in place

• Affordable diaphragm pumps
• Flexible tubing and barbed fitting connections
• 3D-printable reservoirs with integrated fittings, standpipe, and septum closure

Entire kit, back

Arduino and motor driver to control pump speeds (potentiostat not pictured)

Prototyping: FDM printing…

Resin printing

PP FDM-printed cell

Resin-printed cell

The fancy version you’re getting…

The software

The chemistry

• Anolyte: \(\ce{3 Zn^2+ + 6e- -> 3Zn_{(s)} }\)

• Catholyte: \(\ce{6I- -> 2I3- + 6e-}\)

• Overall: \(\ce{3Zn2+ + 6I- -> 3Zn_{(s)} + 2I3- }, E^\ominus = 1.298 V\)

• Parasitic reaction: \(\ce{6I- + O2 + 2 H2O -> 2I3- + 4OH- }\)

Why Zn/I?

• Easy to source reagents

• Low-cost reagents

• Compatible with microporous membranes

• Works with readily available paper as membrane

• Dendrites are a non-issue with microporous membranes

• No detectable hydrogen evolution

• Acceptable energy density (>20Wh/L)

• No strong acids or bases needed

• Low toxicity (but don’t drink it)

Current performance

• Coloumbic efficiency: 88%

• Energy efficiency: 71%

• Accessible energy density: 8.9 Wh/L

Avenues to explore

• Hydraulic flow from anode to cathode across microporous membrane
• Durability of separator membrane
• Long term cycling
• Use of other microporous separators (Daramic for example)
• Modifications of microporous separator (PVA for example)

You can help!

• Documentation
• Cell design
• Electrolyte design
• Growing the community
• Scale-up!

https://fbrc.dev

Acknowledgements

• Josh “Bolt Breaker” Hauser, Sanli Faez & FAIR Battery team
• Daniel Fernández Pinto
• Conference organizers!

References

Arenas, L. F., F. C. Walsh, and C. Ponce de León. 2015. “3D-Printing of Redox Flow Batteries for Energy Storage: A Rapid Prototype Laboratory Cell.” ECS Journal of Solid State Science and Technology 4 (4): P3080. https://doi.org/10.1149/2.0141504jss.

“C-Tech Innovation: C-Flow 1×1 Electrochemical Cell.” 2024. https://www.ctechinnovation.com/product/c-flow-1x1/.

“Electrocell: Micro Flow Cell.” 2021. https://web.archive.org/web/20210615002040/https://www.electrocell.com/products/electrochemical-flow-cells/micro-flow-cell.

Irving, P., R. Cecil, and M. Z. Yates. 2021. “MYSTAT: A Compact Potentiostat/Galvanostat for General Electrochemistry Measurements.” HardwareX 9 (April): e00163. https://doi.org/10.1016/j.ohx.2020.e00163.

“Lab-Cell by Pinflow.” 2024. http://www.pinflowes.com/Products-research-detail1.html.

Milshtein, Jarrod David. 2017. “Electrochemical Engineering of Low-Cost and High-Power Redox Flow Batteries.” PhD thesis.

“MTI Intl: Complete Testing Package for Vanadium Redox Flow Battery.” 2024. http://www.mtixtl.com/CompleteTestingPackageforVanadiumRedoxFlowBattery-EQ-VRFB-CTP.aspx.

O’Connor, Hugh, Josh J. Bailey, Oana M. Istrate, Peter A. A. Klusener, Rob Watson, Stephen Glover, Francesco Iacoviello, Dan J. L. Brett, Paul R. Shearing, and Peter Nockemann. 2022. “An Open-Source Platform for 3D-Printed Redox Flow Battery Test Cells.” Sustainable Energy & Fuels 6 (6): 1529–40. https://doi.org/10.1039/d1se01851e.

“Redox-Flow.com: A-Cell, Redox Flow Battery Test Cell.” 2024. https://redox-flow.com/shop/redox-flow-battery-test-cell/.

“Scribner: Redox Flow Cell Test Fixture.” 2024. https://www.scribner.com/products/redox-flow-cell-testing/redox-flow-cell-test-fixture/.

Workshop

Can you put together a cell that doesn’t leak?