Lithium-ion batteries have become an indispensable part of our everyday lives. Conventional solvent-based electrode production delivers very good results, but is characterized by high resource and energy consumption. Scientists at Fraunhofer ISIT are working on how production can be carried out more cost-effectively and in a more environmentally friendly manner, focusing on solvent-free production of the electrodes.
This is because cost-effective and at the same time environmentally friendly production methods are a must for future battery cell production in order to serve the numerous fields of application.
As a rule, electrode foils are manufactured in larger quantities in a roll-to-roll process. In coating plants, the substrate material, which is on large rolls, is continuously unwound over a number of rollers and coated with the electrode material. In this process, a suspension of solvent, active material and a binder, which ensures the adhesion of the material, is applied to a metal foil. The coated electrode foil then passes through a drying oven and is finally rewound onto another roll. These plants are very large; they can be up to a hundred meters long, depending on the duration of the drying process.
This production process has several disadvantages: the preparation of the suspension takes a very long time, the solvent is harmful to the environment, and due to the long drying time in the oven, the process itself is very energy-intensive.
For this reason, the ISIT scientists rely on a solvent-free dry coating process. They produced a powder mixture of active material, conductive additives and a suitable binder. In order to produce as uniform an application as possible and precisely defined layer thicknesses, this powder mixture is applied to the substrate using a special spreading process.
The powder application quantity can be precisely adjusted by the spreading parameters, as well as via the throughput speed of the carrier film in the machine. In principle, the scientists faced the same challenge as a confectioner who wants to spread powdered sugar on his cake as evenly as possible, without lumps. The material is then fixed to the substrate in a short temperature process.
The new solvent-free dry coating process patented by ISIT for the production of Li-ion battery electrodes shows great promise. With comparable electrochemical properties to electrodes from established production, this new process will not only enable significantly more compact production lines in the future, but also primary energy savings of up to 50 %, since the long and energy-intensive drying sections during production are eliminated. Both the time savings in the production of the powder mixture and the significantly reduced energy requirements during coating, due to the elimination of drying, offer optimum conditions for reducing the use of resources and costs.
“The dry coating technology has the potential to significantly reduce the costs and emissions of electrode production compared to the processes commonly used today. The process developed at ISIT thus makes a direct contribution to the development of economical and environmentally friendly storage technologies for mobile and stationary applications,” summarizes the head of the project at Fraunhofer ISIT, Jannes Ophey.