A simple change to the orientation of graphite flakes could dramatically alter the specs for Li-ion batteries
Battrion, a graphite start-up located in Zurich and a spin-out from Zurich’s Federal Institute of Technology, this month announced that it had won a 100,000 euro prize from Inno Energy, an innovation promoter funded by 23 large European energy and tech companies and universities. These include Schneider, Engie, Enel, Total and Uppsala University.
Battrion’s prize was awarded to reflect its patented approach to manufacturing anodes for lithium batteries.
An average EV battery contains around 25 kg of graphite anodes, at a cost of around US$10 per kg. Some 50 million kg per year are currently used for EV batteries. The cost of graphite is one small part of the drive to reduce the cost of lithium-based energy storage, but its charging performance is a more significant limiting factor for charge rates, and to a lesser extent cycle life.
When a lithium battery with a graphite anode is charged, lithium ions congregate around the anode as they “queue” to embed themselves in the porous carbon, in a process called intercalation. The speed of this intercalation defines the battery’s charge rate.
The shape of the graphite at the anode is a key factor for intercalation rates, as it determines how easily, and therefore how quickly, lithium ions can transit into the carbon matrix. Lithium ions need time to settle between the sheets of graphite, and this is one factor that limits charging speed.
Obviously, as the lithium ions intercalate the volume of the graphite anode expands. With graphite that increase is a manageable 10%. With silicon it is an impractical 400%, a significant obstacle to the use of silicon, even though silicon anodes offer a 10-times up-step in charge density.
Graphite for anodes is generally sourced either from naturally occurring graphite or from coke produced as a by-product of oil refining, and comes in two formations – flaked and spherical.
Flaked graphite is more common, and cheaper, but has the disadvantage that the flakes tend to overlap horizontally. This arrangement slows the lithium migration/intercalation step, and so reduces the maximum charge current and increases charge time.
Spherical graphite forms faster migration channels, but is considerably more expensive, since it is manufactured from flaked graphite with substantial inputs (of hydroflouric acid, among other reagents, and energy/heat) and with substantial wastage. 70% of the starting material is lost. China is the principal producer of spherical carbon.
Battrion’s process orients flakes at right angles to the carbon anode, so creating shorter, easier migration channels without using expensive spherical graphite.
Battrion’s patent filing reveals that its approach is to mix graphite powder with a binder, and then apply a magnetic field of at least 1 Tesla to the composition while it sets on a substrate (which will ultimately be bonded to the battery’s collector).
The magnetic field is applied for between 0.1 seconds and 10 minutes, depending on the viscosity of the composition being used. The binders used include vinyl cellulose, cellulose resin, phenol resin, thermoplastic resin and thermosetting resin, and binders are removed from the final anode by heat treatment, before the substrate is cut or shaped to fit its intended battery cell.
Battrion’s process therefore not only offers a potentially significant step forward in charge rates, but also offers the rapidly expanding battery sector a way of cutting anode costs and diversifying from a single global source.
Battrion’s technology is still very much at the laboratory stage, but looks appealing enough to draw heavyweight interest from the global tech VC market or from battery manufacturers.