Dry Coated Electrode - Tesla's Acquisition of Maxwell

If you’ve taken the Battery Masterclass, you know that the electrode material which includes the binder and the active material are mixed into a slurry before they are applied evenly on the current collector to form an electrode. 

The process of manufacturing electrodes needs energy, water and a lot of floor space in a manufacturing plant. Maxwell Technologies invented a way of applying a dry mixture onto the electrodes which they claim takes much less floor space, energy during manufacturing and is also higher performing.

The dry electrode manufacturing process comprises of 3 main steps 

• Dry powder mixing
• Powder to film formation
• Film to collector lamination
• Drying in vacuum at 120 degrees C to remove moisture

This technique was initially invented for manufacturing their ultra-capacitor line of products. It was later adapted to work with lithium ion batteries as well. In the above graph, it can be seen that the dry coated electrode performs better in terms of capacity retention, and is also shown to have a stable charge / discharge characteristics.

According to Maxwell, their dry coating electrode technology renders a unique electrode micro-structure in which the polymer binder network allows for high ionic conductivity and intimate electronic contact between active materials and the conductive carbon network.

So a dry coated electrode will save on manufacturing costs and has advantages such as better capacity retention as well as high ionic conductivity through the electrode. Maxwell technologies was acquired by Tesla in 2019.

As Tesla has its patents opened to the public, we are not completely sure if the patent on Maxwell’s dry cell coating process is also now open to the public, this is something to consult a lawyer if you want to use such a process in your cell assembly.

Regardless, there are a few important things to be learned here. The first is that energy density of cells is a critical factor considered, especially in the automotive industry. Lithium ion battery technology is especially powerful in this area and is able to pack a lot of energy in a small amount of space / weight. Secondly, to analyze a new cell manufacturing process, there are some critical parameters to be considered for comparison. These are

• Manufacturing , assembly cost, floor space, energy and water consumption
• Capacity retention over many cycles
• Safety tests like overvoltage, overtemperature and nail penetration.
• Charge, discharge voltage profile of the completed cell with respect to specific capacity of the cell. That is the amount of charge in Ah divided by the weight of the cell. 

The top graph shows the voltage profile of the anode, and the bottom shows the voltage profile of the cathode. The resultant voltage profile of the cell would be the difference of the two. Detailed analysis of these graphs is the subject for another paper, as there are many things to consider when examining the voltage profile of the anode and cathode.