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.