Cellfion ($1M to develop cellulose membranes for energy storage applications)

Cellfion, a Swedish cleantech startup founded in 2021, develops ion-selective membranes and nanoparticle dispersion that are natural-based and polyfluoroalkyl-free. These materials are used in energy storage and conversion devices, such as redox flow batteries, fuel cells, and water electrolyzers.

Challenges: renewable energy storage

The use of solar cells and wind turbines to generate clean electricity is on the rise. Ideally, the entirety of the intermittent electricity generated would be put to use. Storage of the surplus electricity is recommended. As a base load supply, the capacity to store their electrical energy would substantially improve the dependability and efficiency of these intermittent renewable energy sources.

Several technologies, including fuel cells and redox flow batteries, show promise as large-scale energy storage systems. Typically, the operation of these systems requires ion-selective membranes. While facilitating efficient ionic transport, such as protons, through the membrane, it also separates redox molecules or gasses in the two cell compartments. Nafion is the most recent and cutting-edge ion-selective membrane. But Nafion is produced in an unsustainable manner and comprises polyfluorinated chemicals that are detrimental to the environment. Furthermore, its high cost hinders the ability to implement energy storage systems on a large scale in a cost-effective manner.

Ion-conductive selective cellulosic membranes have been applied in energy storage systems, such as lithium- or sodium-ion rechargeable batteries, redox flow batteries, and fuel cells. Cellulose is abundant, low-cost, and has excellent mechanical properties. It is a biopolymer with abundant hydroxyl groups along the polymer chain. These abundant hydroxyl groups allow various chemical functionalizations and the ability to form networks in different size ranges. However, the proton conductivity of cellulose itself was insufficient for energy storage applications.

Cellfion Technology

Cellfion develops proton-conductive selective nanocellulose membranes with excellent performance. Cellfion membrane is made through the processes of chemical modification of the surface of nanofibers and the crosslinking of cellulose nanofibers.

The introduction of aldehyde (-CHO) and sulfonic acid (-SO₃⁻) groups to the surface of nanofibers results in a negatively charged environment in the pores of the membrane. This facilitates the ionic transport of positively charged ions, such as protons, while preventing negatively charged or large compounds from passing through the membrane. The crosslinking of nanofibers limits swelling of the membrane and achieves the desired small pore sizes for ion-selective transport.

Cellfion membrane

The diagram below illustrates the structure of the chemically modified Cellfion membrane.

Cellfion’s crosslinked cellulose nanofiber membrane with functional groups in pores (ref. WO2023046735A1).
Cellfion’s crosslinked cellulose nanofiber membrane with functional groups in pores (ref. WO2023046735A1).

The membrane is crosslinked cellulose nanofiber materials. The crosslinking retains the structural integrity of the membrane and restricts its swelling in water or other solvents. The membrane contains aldehyde (-CHO) and sulfonic acid groups (-SO₃⁻) on the surface of nanofibers. These functional groups provide a negatively charged environment within pores, which facilitates the ionic transport of positively charged ions through the membrane. Negatively charged or amphiphilic compounds are prevented from passing through the membrane.

Cellfion membrane fabrication

The fabrication of Cellfion membrane begins with the oxidation of fully bleached cellulose fibers. The cellulose nanofibers that have been completely bleached contain abundant hydroxyl (-OH) groups, which readily afford chemical modifications, as depicted in the diagram below.

The chemical modification nanocellulose for making Cellfion membrane (ref. WO2023046735A1)
The chemical modification nanocellulose for making Cellfion membrane (ref. WO2023046735A1).

The modified fibers are then subjected to high-pressure homogenization to produce separated nanofibers slurry. The slurry is then utilized in the fabrication of membranes.

The fabrication of Cellfion membrane includes the following steps:

  1. The fully bleached cellulose fibers are subjected to oxidation by a sodium metaperiodate (NaIO₄) solution to introduce aldehyde (-CHO) groups to the surface of the cellulose nanofibers.
  2. Some aldehyde groups are sulfonated by adding sodium bisulfite (NaHSO₃) solution. This results in the introduction of sulfonic acid (-SO₃⁻) groups to the surface of the cellulose nanofibers.
  3. A high-pressure homogenization process is used to get the chemically modified cellulose nanofibers in their free form, which means they are not bound together.
  4. An aqueous slurry of the above chemically modified cellulose nanofibers is introduced into a mold. The membrane is formed by dewatering the slurry in the mold by evaporation at an elevated temperature within the range of 4080 ºC.

The fabricated membranes showed excellent homogeneity, low porosity, and stability in an aqueous environment, originating from the cross-linking of aldehyde groups.

Cellfion membrane performance

The Cellfion membrane shows more efficient proton transport compared to other cations in the cellulose membrane, owing to the abundance of both −OH and −SO₃ groups in combination with the small pore size.

In certain application cases, such as aqueous redox flow batteries, the cellulose-based membrane separator largely outperformed the commercial Nafion 115 membrane in terms of device functional stability.

Cellfion Patent

  • WO2023046735A1 Cellulose membrane for a redox flow battery

Cellfion Technology Applications

Redox flow battery

Redox flow batteries are considered a promising option for medium to large scale energy storage. The membrane in these batteries prevents cross-mixing of the positive and negative electrolytes, while still allowing the transport of ions to complete the circuit during the passage of current. Cellfion’s membranes are designed for use in these batteries, offering a sustainable and cost-effective alternative to traditional membranes.

PEM fuel cells

Proton exchange membrane (PEM) fuel cells use hydrogen and oxygen to produce electricity, heat, and water through a chemical reaction. The ion-exchange membrane is a critical component of these fuel cells. The Cellfion membrane facilitates the selective passage of protons while blocking the flow of electrons and other gasses.

PEM fuel cells have a wide range of use cases, including power sources in light electric, hybrid, heavy transport, and material handling vehicles, backup power for buildings, off-grid power for applications like telecom stations, and mega-watt sized backup or off-grid power systems for industrial plants or municipalities.

Electrolyzers

Electrolyzers are devices that use electricity to split water into hydrogen and oxygen, a process known as electrolysis. Cellfion’s membranes can be used in electrolyzers for applications such as hydrogen for transportation, aviation hydrogen fuel production, and energy storage.

Cellfion Products

Cellfion’s primary product is an ion-selective membrane made from cellulose derived from wood. These membranes are used in energy storage and conversion devices, such as redox flow batteries and fuel cells.

Cellfion’s membranes are free of per- and polyfluoroalkyl substances (PFAS), a group of man-made chemicals that have been associated with adverse health effects. The European Union is planning to phase out these substances, which are often used in commercial membranes, in the coming years. Cellfion’s PFAS-free membranes offer a promising alternative that aligns with the EU’s environmental and health objectives.

Cellfion Funding

Cellfion has raised a total of SEK14M in funding over a Seed round raised on Aug 31, 2022.

Cellfion Investors

Cellfion is funded by 5 investors:

LIU Invest and Voima Ventures are the most recent investors.

Cellfion Founder

Liam Hardey, Magnus Wikström, and Ulf Troedsson are Co-Founders.

Cellfion CEO

Liam Hardey is CEO.

Cellfion Board Member and Advisor

Magnus Wikström and Ulf Troedsson are Board Member.

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