Page 83 - Read Online

Page 4 of 14 Kühn et al. Energy Mater 2023;3:300020 https://dx.doi.org/10.20517/energymater.2023.07

coin cell parts and electrodes to the DR atmosphere was kept to a minimum amount of time (< 10 min).
Consequently, the ICCA trapped inside the assembled coin cells remained the only major influential
difference in this study.

Materials
Lithium metal foil (Honjo Lithium GmbH., Ltd., 300 μm thickness, 99.9%) was stored in an argon-filled
glovebox (MBraun Labmaster, H O and O content < 0.1 ppm, N content < 5 ppm). NMC811 electrodes
2
2
2
with an active mass loading of 1.03 mAh cm , purchased from Custom Cells, were dried at 120 °C in
-2
vacuum for at least 24 h before use and stored in an argon-filled glovebox (MBraun Labmaster, H O and O
2
2
content < 0.1 ppm, N content < 5 ppm). All lithium metal and NMC811 electrodes used in this study
2
originated from the one respective batch/sheet of battery grade lithium and NMC811 cathode material to
achieve a high level of comparability for all conducted experiments.
The study utilized three organic carbonate-based electrolyte formulations. The baseline electrolyte (BE)
[1.2 M LiPF in EC:EMC 3:7 (w/w)] and the two film-forming additive-containing electrolytes AE-VC
6
[1.2 M LiPF in EC:EMC 3:7 (w/w) + 5 wt.% VC] and AE-FEC [1.2 M LiPF in EC:EMC 3:7 (w/w) +
6
6
6.09 wt.% FEC], purchased from E-lyte Innovations GmbH, were used as received for coin cell 2032
assembly (for exact formulations, Supplementary Tables 1-3). The electrolytes were stored in an argon-filled
glovebox (MBraun, H O and O content < 0.1 ppm, N content < 5 ppm).
2
2
2
Coin cell assembly
Two-electrode coin cell assembly was performed in an argon-filled glovebox (MBraun Labmaster, H O and
2
O content < 0.1 ppm, N content < 5 ppm) or dry room (-60 °C dew point). The exact procedure for cell
2
2
assembly in the dry room is discussed in the “study design” chapter of the experimental section. In each
coin cell, electrodes with a 12 mm diameter, an electrolyte volume of 30 µL with one layer of Celgard 2500
(16 mm diameter), and two 0.5 mm stainless steel spacers were used to form the battery stack shown in
Figure 1.

Stripping/Plating and galvanostatic cycling experiments
Stripping/Plating experiments of Li||Li symmetric cells and galvanostatic cycling of NMC811||Li cells were
conducted at 20 °C using a MACCOR battery cycler (MACCOR Series 4000).

Stripping/Plating experiments in Li||Li cells were carried out for 1,000 charge/discharge cycles at a constant
current of 0.5 mA cm , with one-hour stripping/plating steps (0.5 mAh cm ). Galvanostatic cycling in
-2
2
NMC811||Li cells was carried out at a constant current density of 0.5 mA cm (equivalent to ~C/2, based on
2
an areal capacity of 1.03 mAh cm ) in the voltage range of 3 V to 4.2 V. Prior to the experiment, each cell
-2
was allowed to rest for 12 h.
Operando electrochemical impedance spectroscopy
Operando electrochemical impedance spectroscopy (EIS) measurements were carried out at a BioLogic
VMP3 workstation. A Li||Li symmetric cell was cycled 50 times (charged and discharged for 1 h each at
0.5 mA/cm ) and the impedance was measured every 5 cycles (10 h). The data of the measured Nyquist
2
plots were evaluated and fitted with BioLogic’s EC-Lab software using an equivalent circuit selection of
R + Q /R + Q /R .
3
3
2
1
2
Post-mortem sample preparation
Electrodes intended for post-mortem analysis (SEM, XPS, ATR-FTIR) were harvested from coin cells which
were opened in an argon-filled glovebox (MBraun, H O and O content < 0.1 ppm, N content < 5 ppm).
2
2
2