When I started working with batteries, I noticed that it was easier to find very detailed academic information about batteries than simple advice about what kind of equipment is needed to build batteries. With googling and discussions with other researchers, I managed to find some information and started to gather the necessary devices and their accessories. In our lab, we had long experience on the printing and coating processes, both in small and pilot scale, so it was relatively easy for me to work with that part. In addition, my other colleagues had a lot of experience on battery characterization in large scale, which of course helped a lot. But we did not have enough capabilities for battery manufacturing. There are some special steps in the workflow, which we had to consider.

As it was not always so easy to find suitable (simple enough) advice, I want to share here some basic requirements for a battery lab. Just in case someone else is facing the same problem or just wants to know how batteries are made. Please however note that this list is a very simplified one.

To start with, you need to be able to build coin cells. But what is a coin cell? If you have a wristwatch that runs with a battery, you most likely have a coin cell inside. Coin cell is the simplest battery type, which is routinely used also for standard battery tests. For preparing coin cells, you need at least this set of equipment:

  1. Slurry mixer
  2. Coating device
  3. Calendering device
  4. Cutters for electrodes and separator
  5. Vacuum oven
  6. Coin cell press (located in a dry room or argon glove box)

Slurry mixing

To make batteries, you need to have a ready electrode slurry, or be able to make it yourself. Slurry is the ink or paste, which contains the relevant battery electrode materials and some solvent. There are several different types of stirrers for slurry making, and selecting the best option depends on the material and the amounts of it. It is a science of its own to create the best possible mixing protocol to make a homogeneous slurry with an optimal particle size distribution. Usually, you need to mix the active material (like graphite powder for the anode, or e.g., metal oxide powder for the cathode) with a conductive additive (usually carbon black), binder, and the solvent. Mixing should in the optimal case be done with a vacuum mixer to avoid having bubbles in the slurry. Ball mills, speed mixers, and Ultra-Turrax type mixers have been used as well. Degassing is good to have if the mixing is not done under vacuum. Otherwise there might be bubbles, which causes problems in the coating step and results in holes or other defects in the electrode layers.


When the slurry is ready, it will be coated on the current collector. In conventional Li-ion batteries, the current collector is a thin foil of copper for the anode or aluminum for the cathode. In the simplest case, you can use a doctor blade coater to deposit the slurry on the current collector. We have used slot die coaters, as we had those available already. With the slot die coater, it is possible to adjust the coating parameters better than with a doctor blade. Slot die coating in lab scale is also already similar (but anyway not the same) to the slot die coating processes in industrial scale and thus speeds up the up-scaling process. For conventional Li-ion battery materials, coating can be done in normal atmosphere. However, it is good to have constant humidity and temperature. This helps to get repeatable results.


After coating and initial drying to remove the solvent, the electrode layers need to be calendered. This means pressing the coated film to achive correct thickness and porosity for the electrode. The film needs to have some porosity to allow the liquid electrolyte to penetrate the layer. However, high porosity decreases the energy density, so an optimum should be found. Optimal porosity depends also on the application. For high-power applications, where energy is needed fast, bigger pores are better as they allow faster ionic diffusion.

A roll-to-roll type calendering device, also called a roller press, is used in pilot and industrial scale. In lab scale, a smaller and planar press can be used. Small roller presses are anyway available also in lab scale.


Mechanical die cutters are usually used for cutting the electrodes and the separator for coin cells. Some of the cutters are easy to use only outside the glovebox, and some are suited better for the glovebox work (but are maybe not as good as the others). Note that storing and cutting of lithium foil, which is needed for standard half-cell tests and Li-metal cells, needs to be done under argon. On the other hand, cutting of graphite or conventional metal oxide electrodes can be done in normal atmosphere, and it is also easier to use the cutters outside the glovebox. Thus, it is better to have cutters available both outside and inside the glovebox. I first bought cutters with only a few size options. But eventually we noticed that it was not enough. Especially as we have been working with several cell types and materials. The delivery times might be long for the cutters. So, if possible, it is good to buy several sizes already at start.

Drying of the electrodes

Drying of the electrodes, or anything that goes into the cells, including the separator, is essential. There should be no water in the cell. Thus, a vacuum oven is needed. We decided to install a vacuum oven inside the glovebox, and we have been satisfied with this solution. It has been very easy and flexible to work with, and it is possible to dry samples and sheets of different size. Another option would be to have an oven integrated into the antechamber, which is used to transport samples inside the glovebox. It is also possible to use a vacuum oven outside the glovebox but then some special tools are required for transporting the samples inside the box. They should not be in any contact with normal atmosphere after vacuum drying to have repeatable and reliable results.

Coin cell assembly

Once the electrodes and separator have been cut and dried, it is time to assemble the cell. This needs to be done under argon, or in a dry room. Standard Li-ion battery electrolytes form toxic gases in normal atmosphere. Thus, it is not just about making good cells. It is, more importantly, about safety. The cells are built first manually in the coin cell cases. This means stacking all layers, including the anode, separator, cathode, spacers, and springs. The electrolyte solution is added also inside the cell. After the cell is stacked, it will be sealed with a crimper. You can check this video Coin Cell Assembly Steps by MTI for more information.

In some cases, e.g., in supercapacitors or beyond lithium batteries, the electrolyte can be water-based. Then it is not possible to use the crimper inside the glovebox as it would be contaminated with water. As it is not very easy to transfer the crimper in an out from the glovebox (it is relatively big), we have also bought a crimper that is placed in normal atmosphere. Note also that sulfur-containing battery materials should not be handled in standard argon gloveboxes as they need a special purification system.

Of course, the cells need to be characterized when ready. I’m not (yet 😊?) an expert in electrochemical characterization of cells. Thus, I will let others to give instructions for that. You can e.g., check this excellent paper Good practice guide for papers on batteries for the Journal of Power Sources for more information. But one thing I want to mention. You need several cyclers for making battery measurements. As I was used to characterization of solar cells or transistors, I naively thought that batteries could be measured as fast (excluding the lifetime tests). But I soon realized that testing a single cell takes several days or even weeks. Thus, for testing several sets of samples and doing enough parallel cells with the same material combinations, you need many cyclers. Better to be prepared for that sooner than later.

Thank you!

I want to end this blog text by thanking all colleagues at and outside VTT for all the help and advise I have received while building up the assembly lab. This is team work, and I have definitely not done this by myself. I want to especially mention my VTT colleagues Olli Sorsa, Tapio Mäkelä and Elina Pohjalainen. Special thanks go also to Aalto University as I was able to build cells and characterize our battery materials in their lab before we had the setup available in our lab.