11 Lithium-Ion Battery—3D Micro-/Nano-Structuring, Modification …
333
compact LCO thin films on stainless steel substrates (Fig. 11.17a). Subsequently,
laser microstructuring of the deposited LCO thin films was investigated using shortpulsed excimer laser sources (ATLEX-1000-I, ATL Lasertechnik GmbH, Germany),
which operated at a wavelength of 248 nm (Fig. 11.17b). The laser pulse repetition
rate could be varied from single pulse up to 1000 Hz and the laser pulse duration
at FWHM was 5 ns. The excimer laser sources were implemented in Promaster
and Micromaster micromachining laser workstations (Optec s.a., Belgium). The
laser fluences could be varied from 0.5 to 10 J/cm
2 . All laser ablation processes
were carried out in ambient air in order to enable the formation of self-organized
microstructures, so-called cones, on the cathode thin film material. The loss of active
material was quite low and is in the range of 0–10 wt% [26]. After structuring laser
annealing of unstructured and laser-structured thin films was carried out to synthesize
the required battery phase (HT-LCO) applying a high-power diode laser (FLS IronScan, Fisba Optik AG) with a maximum average laser power of 50 W at an operating
wavelength of 940 nm. The laser beam had a focus diameter of 1 mm on the sample
surface. The temperature on the sample surface could be controlled inline whereby a
pyrometer (FLS PyroS, Fisba Optik AG) was connected to the laser power management system. The annealing temperature could be adjusted and precisely controlled
from 120 to 700 °C. Finally, a C60 coating was realized on 3D-HT-LCO by applying
RF plasma-assisted thermal evaporation (RF-PATE, Fig. 11.17c). The deposition
of C60 thin films took about 5 min. The mode of operating of RF-PATE has been
described in detail elsewhere [79, 82].
After laser annealing, the surface morphology of the cathode thin film consists of
small grains with a size in the range of 100–200 nm in diameter. The laser annealing
process was performed at 500 °C for a duration of 17 min [26, 31]. The precise control
of the thickness of the C60 coating on top of the 3D-HT-LCO cathode is a critical
parameter, since it determines both the solid electrolyte interface and the electronic
conductivity and it should enable high mechanical strength during electrochemical
cycling [76]. It was shown in previous studies by Lee et al. [80, 84] that a C60thickness of about 80 nm is most appropriate for cell operation.
11.4.2 Electrochemical Performance of Passivated LCO Thin
Film
The cathodes were assembled in coin cells with lithium as counter electrode and
electrolyte made of 1 M LiPF6 in ethylene carbonate, ethyl methyl carbonate, and
dimethyl carbonate (volume ratio 1:1:1). The galvanostatic cycling was performed
in a widened voltage window of 3.0–4.5 V which delivers initial discharge capacities
of 150, 159, and 175 mAh/g for HT-LCO, 3D HT-LCO, and C 60 @3D HT-LCO,
respectively. The coulombic efficiency (CE) of C 60 @3D HT-LCO is highest (94%),
followed by 3D HT-LCO (92%) and pristine HT-LCO (88%). A higher CE value
reflects a lower irreversible loss of capacity, which is mainly due to a suppression of
333
compact LCO thin films on stainless steel substrates (Fig. 11.17a). Subsequently,
laser microstructuring of the deposited LCO thin films was investigated using shortpulsed excimer laser sources (ATLEX-1000-I, ATL Lasertechnik GmbH, Germany),
which operated at a wavelength of 248 nm (Fig. 11.17b). The laser pulse repetition
rate could be varied from single pulse up to 1000 Hz and the laser pulse duration
at FWHM was 5 ns. The excimer laser sources were implemented in Promaster
and Micromaster micromachining laser workstations (Optec s.a., Belgium). The
laser fluences could be varied from 0.5 to 10 J/cm
2 . All laser ablation processes
were carried out in ambient air in order to enable the formation of self-organized
microstructures, so-called cones, on the cathode thin film material. The loss of active
material was quite low and is in the range of 0–10 wt% [26]. After structuring laser
annealing of unstructured and laser-structured thin films was carried out to synthesize
the required battery phase (HT-LCO) applying a high-power diode laser (FLS IronScan, Fisba Optik AG) with a maximum average laser power of 50 W at an operating
wavelength of 940 nm. The laser beam had a focus diameter of 1 mm on the sample
surface. The temperature on the sample surface could be controlled inline whereby a
pyrometer (FLS PyroS, Fisba Optik AG) was connected to the laser power management system. The annealing temperature could be adjusted and precisely controlled
from 120 to 700 °C. Finally, a C60 coating was realized on 3D-HT-LCO by applying
RF plasma-assisted thermal evaporation (RF-PATE, Fig. 11.17c). The deposition
of C60 thin films took about 5 min. The mode of operating of RF-PATE has been
described in detail elsewhere [79, 82].
After laser annealing, the surface morphology of the cathode thin film consists of
small grains with a size in the range of 100–200 nm in diameter. The laser annealing
process was performed at 500 °C for a duration of 17 min [26, 31]. The precise control
of the thickness of the C60 coating on top of the 3D-HT-LCO cathode is a critical
parameter, since it determines both the solid electrolyte interface and the electronic
conductivity and it should enable high mechanical strength during electrochemical
cycling [76]. It was shown in previous studies by Lee et al. [80, 84] that a C60thickness of about 80 nm is most appropriate for cell operation.
11.4.2 Electrochemical Performance of Passivated LCO Thin
Film
The cathodes were assembled in coin cells with lithium as counter electrode and
electrolyte made of 1 M LiPF6 in ethylene carbonate, ethyl methyl carbonate, and
dimethyl carbonate (volume ratio 1:1:1). The galvanostatic cycling was performed
in a widened voltage window of 3.0–4.5 V which delivers initial discharge capacities
of 150, 159, and 175 mAh/g for HT-LCO, 3D HT-LCO, and C 60 @3D HT-LCO,
respectively. The coulombic efficiency (CE) of C 60 @3D HT-LCO is highest (94%),
followed by 3D HT-LCO (92%) and pristine HT-LCO (88%). A higher CE value
reflects a lower irreversible loss of capacity, which is mainly due to a suppression of