New, Efficient Process for the Rounding of Graphite 

Due to its use as a material for anodes in lithium-ion-batteries, graphite is of great importance in the context of electromobility. In order to obtain the high purity required for battery applications, the finely-distributed, so-called flake graphite which occurs naturally in stone, must be processed in various steps.

Spherical graphite (SPG) is ideal for use as a raw material for anodes. Its smooth, small surface prevents flaking and ensures low irreversible capacity loss and long service life. Due to its high tap density, high charging is achieved and consequently energy density is higher.

The NETZSCH business unit Grinding & Dispersing and Dorfner ANZAPLAN have joined forces to find a more efficient solution for graphite rounding to overcome the disadvantages of the previously widespread used process requiring more than 20 classifier mills installed in rows: In a first step, the flock graphite is pre-ground to the optimum initial particle size for spheroidization in a classifier mill or fluidized bed jet mill. The actual particle rounding process takes place directly downstream in the newly designed NETZSCH GyRho Rounding Unit which is available in various construction sizes and can be specially designed to suit the necessary output quantity. For larger throughput volumes two (or more) machines can be operated simultaneously and can replace the train of 20 machines or more as mentioned above.

The increase in efficiency and the advantages which the new process-optimized system offers compared to the previous standard-plant train are impressive: Plant availability has been increased by 30 % in comparison to previously used processes as the number of machines and consequently the probability of breakdown is reduced drastically. For this reason, maintenance costs are reduced by almost 90% and the compact setup means the plant can be installed in a 60% smaller space. In addition to this, the NETZSCH/Dorfner ANZAPLAN system requires only half the installed power of a plant train while achieving the same production capacity and using 60 % less energy due to its optimized mode of operation.

Product yield is a decisive improvement in the process. By optimizing the design of the grinding chamber and reducing the number of components, it was possible to increase yields of 30 to 40% achieved by the standard system to 60 to 65%. At the same time, using specific settings, it is possible to achieve the maximum yield of final product with the desired quality. Quality criteria such as distribution width, tap density and particle size can be influenced by varying the process parameters. In this way, using the newly developed NETZSCH and Dorfner ANZAPLAN GyRho system, all qualities required by the market, such as spherical graphite with a tap density of more than 960 g/l and a d50 value of 16.8 µm (yield based on a raw material volume of > 60 %) are achievable.

Thus, using this process developed by NETZSCH and Dorfner ANZAPLAN, not only a higher plant availability and raw material efficiency are achieved at the same production capacity but also a significantly higher product quality. The mentioned improvements result in an approximate 35% reduction of operational costs, demonstrating the technical superiority of this newly developed system solution which has decisively improved the economic efficiency of graphite rounding. In NETZSCH´s well-appointed application laboratory in Hanau, Germany, which forms part of our comprehensive service offer, graphite-rounding tests can be carried out on a laboratory scale and up to a production scale. Material samples are processed under production conditions and their behavior analyzed to achieve the best result at highest efficiency.