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Page 6 of 24 Boaretto et al. Energy Mater. 2025, 5, 500040 https://dx.doi.org/10.20517/energymater.2024.203

thickness of 20 µm by an automatic film applicator 1137 (SHEEN Instruments). The electrode was dried in a
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convection oven at 110 °C for 15 min. The dried electrode with a final loading of 13 mg NMC-811 cm was
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compressed by a laboratory hydraulic roll calender (DPM Solutions, Canada) to 3.0 ± 0.1 g cm density and
finally dried under dynamic vacuum at 120 °C for 16 h in the dry room. NMC-811||Li-Cu coin cells were
fabricated with the spray-dried NMC-811 cathode active material.

Owing to the limited availability of the spray-dried active material, NMC-811||Li-Cu single-layer pouch
cells were fabricated with commercial NMC-811 (T81RX, Targray). Firstly, a 1 kg slurry batch with the
abovementioned formulation was prepared in a dry room (dew point of -40 °C) using a mechanical mixer.
Then, the one-sided positive electrode coating of a carbon-coated 20 µm aluminum current collector
(Gelon) was carried out using a modified base-coater pilot narrow width machine (up to 300 mm) with a
dryer comprising three separated 1-meter-long zones (COATEMA). Finally, the cathode application with
confirmed loading level (2.5 mAh cm , 13.8 mg NMC-811 cm ) was calendered at room temperature until
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reaching an electrode density of 3.0 ± 0.1 g cm using roll press LDHY400-N45 (Naknor). Before pouch cell
assembly, notched cathodes with dimensions of 50 × 60 mm were dried under dynamic vacuum at 120 °C
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for 16 h in a dry room (dew point of -50 °C). Lithium metal anodes with a thickness of 50 µm (Albemarle)
and dimensions of 50 × 60 mm were manually cut inside a dry room (dew point of -50 °C) right before
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pouch cell assembly.
Cell assembly and testing
All coin cells (Hohsen Corp.) were assembled in an Ar.-filled glovebox (MBraun) with H O and O
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concentrations below 1 ppm, and with a manual coin cell crimper (Hohsen Corp.).
The plating/stripping performance of QSPEs was tested at 25 °C, in Li||Li symmetric coin cells with Li
electrodes supported on Cu sheets (14 mm-diameter, ABEE). The cells were cycled galvanostatically with a
Neware battery tester at 25 °C and at a fixed capacity of 2 mAh cm . Five cycles were performed at
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0.2 mA cm (C/10), followed by 5 cycles at 0.4 mA cm (C/5), 0.67 mA cm (C/3), 1 mA cm (C/2) and
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2 mA cm (C/1). Thereafter, the cells were cycled at C/10 until failure.
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Plating/stripping coulombic efficiency was determined by cycling Cu||Li cells, with 500 µm-thick Li discs
(14 mm diameter) as counter electrodes and Cu discs (16 mm diameter) as working electrodes. Thick Li foil
was used to avoid any effect due to depletion of the negative electrode, as the study of the deposition and
stripping process on the Cu foil was the target of this test. Tests were conducted with a Neware battery tester
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at 25 °C. Firstly, a current of -0.1 mA cm was applied for 20 h, followed by application of a positive current
with the same amplitude, until a cutoff voltage of 0.2 V was reached. This full plating/stripping cycle was
performed twice and served as a conditioning cycle, to establish a stable SEI on the Cu foil surface. Then, a
plating half cycle was performed, with the same conditions described above, with the aim of creating a Li
reservoir on the Cu foil. Thus, this Li reservoir corresponds to an area capacity of 2 mAh cm . Thereafter,
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fifty short plating/stripping cycles were performed, with a current density of 0.1 mA cm and a half cycle
time of 2 h. In these short cycles, a capacity of 0.2 mAh cm is cycled back and forth. Finally, a positive
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current of 0.1 mA cm was applied, until the cutoff voltage of +0.2 V was reached. The coulombic efficiency
of the first 2 cycles was calculated by the ratio of the stripping capacity to the fixed plated capacity. In
addition, the average coulombic efficiency during the intermediate short cycles was calculated by :
[56]