Know-how in graphite spheroidisation for lithium-ion batteries

The industry is currently facing a major challenge here: In cell production, graphite as a raw material must be used more effectively. The solution to this is the rounding of the normally platelet-shaped graphite particles. Rounding has numerous advantages. For one thing, it increases the tap density and thus ensures a higher volumetric energy density of the battery anode. The improved intercalation kinetics increase the charging capacity and thus also the fast-charging capability. It also makes the battery more durable.

"The existing processes for rounding graphite are very energy-intensive and additionally often have low yields of 30 to 50 %. Thus, in the current production of rounded graphite, a large part of the graphite for use in lithium-ion batteries is lost during processing. To make the graphite rounding process more efficient, we have now developed a new process that requires fewer machines than before. This not only saves space, but also effort for maintenance and service, as well as energy", explains Paul Woodward, Operations Director Minerals & Metals Division at Hosokawa Alpine. Since natural graphite and synthetic graphite place different demands on graphite rounding, Hosokawa Alpine offers machine solutions for both tasks.

Natural graphite is platelet-shaped and usually requires more energy and a higher stress intensity during rounding than synthetic graphite, which is usually already much more spherical after grinding. Hosokawa Alpine has therefore developed a special machine for rounding natural graphite: the Alpine Particle Rounder APR.

"Here, the graphite is pre-ground on a classifier mill. Subsequently, the graphite is rounded in batches with subsequent dedusting by high efficient classification. In this way, we were able to increase the tap density to more than 900 g/l and make up to 80 per cent of the raw material usable," explains Paul Woodward. The APR also scores points for short process times and high throughputs with low specific energy consumption. The APR process reaches tremendous energy savings in the range of 50 % compared to common classifier mill processes. Variable target finenesses from x50 = 10-12 µm up to x50 = 18-22 µm are easily possible with the APR.

For the rounding of synthetic graphite, Hosokawa Alpine has the Zirkoplex ZPS classifier mill in its portfolio. Flexible fine grinding and classifying are implemented with only one pressure shock resistant machine. The graphite is first pre-ground on the classifier mill with the energy-saving designed grinding unit. Rounding and classifying are then carried out in batches.

The Zirkoplex ZPS also increases the tap density of the graphite to more than 1000 g/l for more storage capacity. Further advantages are high throughputs and process yields of up to 90 percent usability of the graphite with low specific energy consumption. Thus, the Zirkoplex ZPS completes the solutions for efficient and contemporary graphite rounding from Hosokawa Alpine.

Materials such as nickel, manganese or cobalt oxide are used in the cathode, but they have to be prepared before they can be processed. Before grinding, the slurries and filter cakes have to be dried in a continuous process. Hosokawa Micron B.V., the Dutch partner of Hosokawa Alpine, offers the right machines for both products. The DMR Flash dryer provides continuous drying for the active material and achieves final moisture contents of less than one percent. For even lower moisture contents, batch dryers such as the Nauta vacuum dryer are the right solution. If difficult volatile substances are processed, the CPD conical paddle dryer can combine temperatures of up to 325°C with full vacuum to achieve extremely low PPM values.

The ultra-fine grinding process for active powders creates smaller particles with a larger surface area in the next step. This ensures optimum battery performance. Charging times, capacity and service life are all improved. “The most common milling solutions for the battery industry are the classifier mill ACM and the fluidised bed opposed jet mill AFG, both of which can achieve extremely fine and narrow particle size distribution. The mills can be used not only for cathode materials such as lithium cobalt oxide or manganese-based precursors, but also for anode materials such as graphite and silicon,” explains Alexander Krauser, Operations Director Chemical Division at Hosokawa Alpine. The classifier mill ACM is protected against wear by a special ceramic design and ensures high product purity. Contamination-free, cool grinding and classifying are also possible in one machine, as with the fluidised bed opposed jet mill AFG. It can be used to produce powders with steep particle size distribution and sharp upper particle size limits in the ultra-fine range. Hosokawa Alpine has also developed machines for graphite rounding, which improves the product properties of the battery anode. With the classifier mill Zirkoplex ZPS for synthetic graphite and Alpine Particle Rounder APR for natural graphite, the bulk density is increased at a high throughput rate, thus ensuring improved battery life, fast-charging capacity and conductivity.

Mixers with high shear force are used for the final coating of the electrode materials. They not only ensure a homogeneous mixture of materials, but also optimised coating with carbon black and binders, so that the conductivity of the battery is further improved. The Cyclomix intensive paddle mixer, the Modulomix modular paddle mixer or the Nauta conical screw mixer from Hosokawa Micron B.V. are all suitable choices here.

Explore more: Graphite rounding for lithium-ion batteries | Alpine Particle Rounder APR | Zirkoplex ZPS | Lithium-ion batteries | ACM | AFG