*2.3. Cell Preparation*

Cells were assembled as coin cells in PAT-Cell or ECC-Ref cells from EL Cell. For constant current cycling and *C*-rate tests, cells were assembled with NCM as the working electrode and graphite as the counter electrode. The polypropylene separator (Freudenberg FS2190) was moistened on both sides with a total of 120 μL of the selected electrolyte before the electrodes were added. For cyclic voltammetry measurements, two electrode cells were assembled with stainless steel or aluminum as working electrode and stainless steel as counter and reference electrode.

## *2.4. Electrochemical Characterization*

All tests were done in a Memmert IPP110 thermal chamber at a constant temperature of *T* = 25 ± 0.1 ◦C. The cell performance was evaluated by cycling tests with constant current charge and discharge with the battery tester CTS from BaSyTec. At the beginning, three preliminary formation cycles were performed at *I* = *C*/10 in a potential range from *U* = 2.5 V to *U* = 4.2 V. Subsequently lifecycle tests were performed at *C*/4.

The cyclic voltammetry measurements were performed with a reference 3000 AE from Gamry. The electrochemical stability was measured by linear sweep voltammetry. The scan rate was set to 1 mVs<sup>−</sup>1, the potential limits were set from −4.3 V to 4.3 V vs. stainless steel.
