Batteries are a key to cut down the man-made carbon dioxide emissions. Electric vehicles are already a cleaner option compared to gasoline cars. However, production of batteries requires energy. It is important to minimize the energy consumption throughout the whole battery value chain. This way the CO2 payback time can be minimized. We can still improve.

In this blog text, I want to introduce one method, which shows high potential to reduce the CO2 emissions from cell manufacturing – dry extrusion coating. But let’s first check the big picture about emissions.

Sources of CO2 emissions

CO2 emissions from battery manufacturing come from mining and refining, production of active materials, and cell manufacturing. The exact amounts of emissions depend on the cell chemistry and on the country where the materials are mined, and cells produced. The more renewable energy is available, such as in the Nordic countries, the lower the emissions are. For more details, you can read a nice paper by Chengjian Xu et al. about the calculations for several Li-ion battery chemistries, showing the status in year 2020 and scenarios for years 2030-2050.

Note that in the case of Na-ion batteries, the emissions are much lower. Björn Mårlid, the CEO of Altris, gave a presentation last month in the Battery Innovation Days. He said that Na-ion batteries have 3 times lower emissions from the extraction of raw materials, when compared to Li-ion batteries. His estimation was that the CO2 emissions from Na-ion battery manufacturing will be as low as 4 kg CO2/kWh in 2030. For Li-ion batteries, the estimations land between 15 and 40 kg CO2/kWh in 2030.

In short, raw materials (from mining to active material production) cause a major part of the CO2 emissions, especially in the case of Li-ion batteries. But cell manufacturing is not insignificant either. Currently, about 25% of the emissions come from cell manufacturing.

How battery electrodes are currently produced

The battery electrodes are currently mostly produced by slot die coating. It means that we have a slurry of active materials and additives in a solvent. For the cathode active materials, the solvent is usually N-methylpyrrolidone (NMP). NMP is used since the common binder material, polyvinylidene fluoride (PVDF), does not dissolve in many other solvents. It is a toxic solvent, and it has a high boiling point. The workers and the environment need to be protected from the chemical, and drying of the electrode layer after coating requires a lot of energy.

Some producers also use water-based slurries, which are safer to use and more sustainable. However, they also need to be dried. And water-based slurries become challenging if we increase the nickel content, and thus sensitivity, in the cathode active material.

Ways to minimize the CO2 emissions

There are several ways to reduce the CO2 emissions from battery manufacturing. We can reduce the scrap rate during cell manufacturing, use raw materials with lower carbon footprint, use lower temperatures in processing and energy efficient production methods. And of course, we should use renewable energy as much as possible.

And note, also the new batteries regulation requires that the carbon footprint of batteries should be reported and minimized.

Dry extrusion coating

In any case, and regardless of the chemistry, it is mandatory to coat the battery electrode electrodes. This requires energy. Thus, developing energy efficient processing methods is a chemistry neutral way to decarbonize the battery value chain. Even if we are not sure that which cell chemistries will be used in future, we can and should think about how to produce the electrodes in a sustainable way.

Dry extrusion is one of the promising methods to minimize energy consumption in electrode coating. Drying and solvent recovery can cause close to 50% of the energy consumption in the cell manufacturing step. Thus, if we can eliminate the use of solvents, we will increase the sustainability of processing.

The extrusion process for electrodes consists of a few stages: dry mixing of the materials inside the extruder, dry coating on the current collector, calendering, and slitting/cutting into a correct shape. The method is especially suitable for solid-state batteries with polymer electrolytes. The polymer electrolyte can even function as a binder, further increasing the energy density. This is something we are developing in the ongoing European SOLiD project. We just got our first cells tested, using a cathode prepared fully without solvents! And it worked quite nicely 😊

Examples like this keep me motivated. The story started a couple of years ago when I realized that we have a group at VTT who is very experienced in extrusion coating and who have extrusion equipment from lab to pilot scale. I then contacted them and proposed to join our forces and use this equipment for making battery electrodes. We decided to build a consortium around this and other ideas and applied for European funding. Luckily, our project was selected to be funded. And now we start seeing the results.

(As a side note, it does not usually go so smoothly. I have several rejected proposals saved under my “Proposals” folder. And many ideas that are still waiting to be funded, or perhaps forgotten.)


I see dry extrusion coating as one of the methods to reduce emissions from battery manufacturing. It is not yet widely in use in industry, but for example Blue Solutions is already using it for solid-state battery manufacturing. I believe others will follow.

In addition to the lower energy consumption, extrusion coating can offer also other benefits. These include avoiding toxic solvents and the ability to make thicker electrodes without cracking. Thicker cathode layers help to increase the energy density, which is important especially for the mobility applications. Also, the production cost can be lowered. A recent paper and a review gave a few examples and summarized the benefits nicely.