High-Performance ECO COM'BAT Cells

By involving actors along the whole value chain and from each part of the knowledge triangle the newly developed battery materials were processed to innovative electrodes and battery cells. This was achieved in the following two steps:

Pre-Pilot Cells

For the improvement of the electrode formulation and cell composition, various test cells were produced at Fraunhofer ISC and CEA on a lab and pre-pilot scale. Different LiFSI-based electrolytes, binders and carbon additives were applied. The amounts of active material (ORMOCER^®- coated NMC 622), nanotubes (Graphistrength^®) and pore former (Porocarb^®) were optimized, the calendaring was varied and the capacities of anodes (standard graphite based) and cathodes (innovative ECO COM'BAT composites) were adjusted to each other.

Pilot Cells

The findings were discussed with the industrial cell manufacturers and transferred to the subsequent pilot production. Several 100 meters of electrodes were manufactured at CEA and Customcells based on the best formulations. Pilot battery cells with high capacities ranging from 2.7 Ah to 24 Ah could be achieved with the large-scale electrodes and final batches of the selected electrolyte. These full cells had a pouch design (10 cm x 10 cm) or cylindrical format (50125). To meet automotive standard requirements, energy and cost efficient production methods were applied.

In consideration of the specifications from the large battery cell manufacturer SAFT, various electrochemical tests were performed at CEA, Customcells and Fraunhofer ISC. Materials, components and cells were fully characterized by CEA, CSIC, ENEA, Fraunhofer ISC and TU Darmstadt. To support the optimization process, the battery performance and battery aging was simulated by VITO with several physically based models.

Pre-Pilot Cells

First battery tests of CEA were performed with ECO COM'BAT pre-pilot electrodes and standard LiPF₆ electrolyte as a first step (53437 test cells with ~0.5 Ah). Initial rate capabilities and cell resistances were measured, followed by cycling stability tests. The cells performed well with a comparatively high cut-off voltage of 4.2 V and a rate of C/2. More than 800 cycles with less than 20 % capacity loss could be achieved. Furthermore, a good rate capability was obtained with more than 80 % capacity remaining at a discharge rate of 2 C.

Pilot Cells

The final pilot cells from the industrial partner Customcells showed significant improvements compared to cells with industrial reference samples. Both scaled-up materials, the ORMOCER^® coated NMC 622 and the lithium salt LiFSI, enabled an extension of the life cycle up to 50 % at a cut-off voltage of 4.3 V. Best results were achieved for the combination of all ECO COM'BAT materials. Commercial reference materials had been an NMC 622 from an external supplier and the standard LiPF₆ electrolyte.

In summary, it can be said that  

• there is an improved cycle life in comparison to cells with industrial reference samples,
• a high voltage stability (up to 4.4 V) and suppressed gas formation
• and a good cycling performance at high rates.