DVS_Bericht_393LP

2.2 Preparation of APS NZSP Deposits
Plasma spraying was carried out by a commercial plasma spray system (GP-80, Jiujiang, China). 430 stainless
steel buttons (15 mm in diameter and 1 mm in thickness) with surface grit-blasted were used as the
substrate to deposit NZSP electrolyte. The plasma jet was generated using a mixture of argon and hydrogen
gases under different spray parameters, which are shown in Table 1. During plasma spraying, the plasma
arc power was changed in three different levels of 32, 36 and 40 kW by altering arc current, while all other
spray parameters were kept constant. To ensure splat interface bonding, the NZSP deposits were prepared
at a deposition temperature of 300 °C. The isolated splats were also deposited on the polished substrate
surface at the deposition temperature of 300 °C at a rapid torch traverse speed of 1000 m/s to examine the
effect of spray particle size on the vaporization loss of Na and P elements. To investigate the effects of the
annealing on the electrical property of NZSP deposits, they were annealed in air at 600 °C, 800 °C and
1000 °C for 2 h, respectively.
Table 1. Plasma spray parameters.
Parameters
Value
Arc current (A) 550, 620, 690
Arc power (kW) 32, 36, 40
Primary gas (Ar) (SLPM) 45
Auxiliary gas (H2) (SLPM) 4
Spray distance (mm) 80
Torch traverse speed (mm/s) 450
2.3 Characterization of the Microstructure and Composition of the Deposits
The surface morphology and cross-sectional microstructure of the powders and deposits were observed
using scanning electron microscopy (SEM, MIRA 3 LMH, TESCAN, Czech). The apparent porosity and ZrO2
content of the deposits were estimated by digital image analyzing method according to the ISO/TR
26946:2011(E) Standard. In the cross-section images of the well-polished specimens, the pores are present
in the coating in a darker contrast than other areas, while the ZrO2 phase is presented in a whiter contrast.
After the binarization, the apparent porosity and ZrO2 content were obtained from the area ratios of pores
and ZrO2 to the total area of specimen. The elemental compositions of the samples were analyzed by the
energy dispersive spectrum (EDS). The crystal structure was characterized by X-ray diffraction (XRD, D8
ADVANCE) analysis with a step rate of 2° min -1 using Cu Kα radiation source in a 2θ range of 10-60°. The
profile and volume of the individual splats were measured using three-dimensional (3D) confocal laser scanning
microscopy (OLS5000, OLYMPUS, Japan).
2.4 Characterization of Electrochemical Performance of ASS-SIB
The functional layers of ASS-SIB battery were deposited in the order of NCO, NZSP and LTO on the
430 substrate using APS at a plasma arc power of 40 kW. Then, silver paste (82%, DAD-87, resistivity
< 5.0×10 −4 Ω·cm) was coated on the surface of both the LTO electrode and the substrate as current collectors.
The APS-sprayed battery was tested in the range of 0.5-2.5 V on the Zahner battery testing system
(Zennium X). The EIS was characterized using CS350 electrochemical workstation (Solartron SI 1260/1287
impedance analyzer) with an AC amplitude of 10 mV in frequency range from 0.1 Hz to 1MHz. The impedance
data were fitted by the ZView software (Scribner Associates Inc). The ionic conductivity (σ) is computed
using equation:
σ = l / (A × R) (2-1)
where l and A are the thickness of deposits and the area of silver current collector, respectively.
3 Result and Discussion
3.1 Effect of Spray Particle Size on the NZSP Splat Composition
The NZSP splats were deposited on the polished alumina substrates with a preheating temperature of
300 °C. Figure 2(a) shows the morphologies of the splats deposited at a plasma arc power of 40 kW. Most of
the splats exhibited a regular disk shape since the spray particles were fully molten before impinging on the
surface of substrate. A few of them exhibited a semi-molten state because of the poor heat transfer within
large particles. The single isolated splat seen from Figure 2(b) showed a smooth surface without cracks,
which may be attributed to the high deposition temperature which reduced the thermal mismatching stress
with substrate. Only small concaves in a black contrast were distributed on the surface of splats due to the
gas entrapment during spraying process.
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DVS 393