High-energy batteries and their production in energy- and resource-saving processes are required for a successful transition to renewable energies and the associated switch to electric mobility. Solvent-free production of battery electrodes by dry coating eliminates the need for a drying step, offering significant potential to improve both process economics and sustainability. In addition, this method allows for the production of electrodes with high area weight without the well-known problem of binder migration that often occurs in the production of wet-coated electrodes.
In this work, a solvent-free processing method is investigated that consists of two main steps. In the first step, the active material (NMC811), the carbon black and the PTFE binder are dry mixed in a twin screw extruder. In the next step, the granules are fed into a two-roll calender to produce free-standing films and laminated electrodes. To achieve cathodes with specific areal capacities, it is essential to coordinate the parameters of the calender-based dry coating process, including line load, roller speed, and friction. Electrode properties such as density, mass loading and pore structure, as well as electrochemical performance, are affected by the adjustment of these parameters. While higher electrode densities allow for high energy densities, excessive calendering can lead to particle breakage or pore network impairment, compromising electrochemical performance. By increasing the friction, thinner films can be produced , By increasing the friction by 10%, it is possible to produce films that are 15% thinner while at the same time the material infeed into the calender gap becomes more challenging. Inconsistent material intake can result in frayed edges and unevenly densified areas, which appear in the form of periodically continuing ridges (fig. 1). While the mass load decreases linearly with increasing friction, the porosity of the film is largely determined by the line load (fig. 2). In order to determine the process-structure-property relationships, cathodes with different electrode properties were produced. The cathodes were examined by means of SEM images, adhesion strength, microscopy and porosity. The electrochemical properties, including capacity, rate performance and cycle stability , were evaluated in coin cells.
These findings contribute to scalable, solvent-free electrode manufacturing, promoting both high performance and sustainable battery production.