Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States

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1 Eric Kazyak a, Kuan-Hung Chen a, Kevin N. Wood a, Andrew L. Davis a, Travis Thompson a, Ashley R. Bielinski a, Adrian Sanchez a, Xiang Wang b, Chongmin Wang c, Jeff Sakamoto a, Neil P. Dasgupta a a Department of Mechanical Engineering, University of Michigan, Ann Arbor, Michigan 48109, United States b Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, 15261, USA, c Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States ALD was carried out in a glovebox-integrated Savannah S200 reactor (Ultratech/Cambridge Nanotech, Inc.). The ability to prevent air-exposure before and after deposition reduces the possibility of reactions leading to undesirable surface reactions that alter the composition and purity of the films prior to characterization. 225 C was used as the substrate temperature for the process, as it falls within the ALD window for all of the constituent processes. A carrier gas flow of 10 SCCM Ultra High Purity Ar during pulses and 20 SCCM during purging was used. Pulse and purge times necessary for saturated growth were determined using ellipsometry and in situ QCM. Lithium tert-butoxide (99.9%, Alfa Aesar), lanthanum tris(n,n-di-iso-propylformamidinate) (Dow Electronic Materials), tetrakis(dimethylamido)zirconium (99.99%, Sigma Aldrich), trimethylaluminum (97%, Sigma Aldrich) were used as precursors with ozone from an ozone generator (Ultratech, Inc.) as the oxidant. Elliipsometry was conducted with a Woollam M-2000 with a Si (100) substrate and data was fit with a Cauchy model. All annealing and XRD was done using MgO (100) substrates. Synchrotron XRD was carried out at Argonne National Laboratory at beamline 33-BM-C with 9.4 or 17.6 kev x-rays. Grazing Incidence XRD was used to reduce the signal from the single crystal substrate and amplify signal from the thin film. For the in situ experiments, a custom airtight annealing chamber with an x-ray transparent beryllium dome was used. Helium was flowed at 10 SCCM during the experiment to maintain an inert atmosphere and reduce absorption of the x-ray beam. An FEI Nova Nanolab 200 was used for SEM analysis. A Nikon LV microscope was used for optical microscopy. The high resolution transmission electron microscopy (HRTEM) images were captured using Titan (FEI, Hillsborough, OR USA) microscope, which is operated at 300 kv and fitted with a spherical aberration corrector for the objective lens. The TEM sample was prepared by touching the lacey carbon TEM grid against the grown sample to pick up the nanowire. A Kratos Axis Ultra was used for XPS analysis. A monochromated Al source was used with 160 ev pass energy and 700x300 µm sample area, and CasaXPS was used for peak fitting with Shirley backgrounds. ICP-OES analysis was done using a Perkin-Elmer Optima 2000 DV, using 1 mg/l yttria internal standard and a set of 7 standards. Calibration curves achieved correlation coefficients above ICP samples were prepared by fully dissolving the ALD film (>100 nm) on samples approximately 4 cm 2 in 1mL aqua regia and then diluting to 10mL for analysis. Three replications of each measurement were performed, and standard deviations were less than 5% of the measured concentration in all cases, and below 1 % in most cases. In-plane impedance measurements were conducted using a microprobe station inside of an Ar filled glovebox. ALD films were deposited onto interdigitated platinum electrodes with a 5 µm gap (Dropsens). Each electrode had 250 fingers each 6760 μm in length. Through-plane conductivity measurements were conducted by sputtering 80 nm of Pt on Si3N4 coated Si, followed by the ALD LLZO coating, and then an array of 310μm x 310 μm Pt electrodes was sputtered on top using a shadowmask after ~5 minutes air exposure. The bottom electrode was exposed by scratching through the ALD film using a diamond scribe, and contacted using a tungsten needle on a microprobe station inside an Ar glovebox. Electrochemical impedance spectroscopy was carried out using a Gamry interface 1000 potentiostat between 1MHz and 1Hz with a 30mV amplitude. An equivalent circuit based on a model developed by Huggins was used. The circuit elements normally associated with grain boundaries were omitted due to the amorphous nature of the films. As expected, the capacitance of the semi-circular feature is ~10-10 F, confirming the resistance values correspond to conduction in the bulk amorphous film. A diffusion element associated with restricted diffusion was used to model transport in the sputtered thin film electrodes. 1

2 Figure S1. Pulse length saturation curves for La(FAMD), LiO t Bu, and TDMAZ with ozone measured by in situ QCM, assuming bulk density. 2

3 Figure S2. Quartz crystal microbalance (QCM) data showing the uptake in mass during the binary processes for La(FAMD) O 3 (a), LiO t Bu O 3 (b), and TDMAZ O 3 (c). The mass uptakes during one repeat unit of the supercycle for the LLZO ALD process showing that each process results in growth when combined (d). Wide view of LLZO ALD process showing linear growth over many supercycles. a) b) Figure S3. Plot showing decrease in La:Zr ration as a function of Li pulse proportion in ALD Supercycle as measured by ICP- OES (a). Plot of average La2O3 mass uptake during subcycles immediately following various base materials (b). La nucleation is dramatically suppressed when the previous subcycle was LiO t Bu-O 3 and significantly increased when the previous subcycle was TDMAZ-O 3. 3

4 Figure S4. EIS spectra showing Nyquist plots for a range of temperatures on the interdigitated electrodes (a) with zoom in on low-impedance region shown in (b). Markers are experimental data and solid lines are fitted curves using equivalent circuit model shown in (c). (d) Ion-beam milled cross-sectional SEM image of ALD film on interdigitated electrode structure. (e) Arrhenius plot for both through-plane and in-plane measurements along with the calculated activation energies for each. Conductivities of the films could only be directly measured down to 100 C due to high impedance. 4

5 Figure S5. (a-f) Low magnification optical images showing evolution of film microstructure after annealing at different temperatures. Phase segregation and clear crystalline grains appear starting at 600 C, with islands forming. These islands remain up to 900C, with smaller grains appearing in both 800 C and 900 C. These smaller grains can be seen in the SEM images shown in (g, k-m), and in the EDS maps shown in (h-j), which show that the smaller grains are aluminum and lanthanum rich, and zirconium deficient. This matches with the perovskite LaAlO 3 impurity observed in XRD patterns observed under those conditions. In addition the film is no longer dense and pinhole free, but rather a porous matrix of interconnected particles as seen in (m). 5

6 Figure S6. TEM image of one LLZO ALD Supercycle on hydrothermal ZnO nanowire showing dense uniform coating of wire structure and sharp interface between film and wire. Figure S7. Synchrotron Grazing Incidence XRD pattern of as-deposited 100 nm LLZO ALD film showing amorphous nature of the film. 6

7 Figure S8. Synchrotron XRD patterns for different annealing conditions showing the lithium deficient phases that resulted from higher temperature anneals. A rapid anneal at 900C in oxygen resulted in a nearly pure pyrochlore film. Annealing in an inert Ar atmosphere allowed some garnet to form, however the lower temperature anneal in a sealed container with a lithium source nearby, as discussed in the main text, resulted in a nearly pure-phase garnet film. Several of the peaks (d = 4.25, 3.8, 3.0, and 2.82Å) could be due to lithium carbonate (Li 2 CO 3 ICSD 61933) but with slight shifts due to temperature and/or interaction with the substrate, and peak intensity changes due to preferred orientation. The peak at d=2.82å could be linked to a lanthanum oxycarbonate (La 2 O 2 CO 3 ) species and the peak at d = 3.0Å could be from a lithium lanthanum aluminate (LiLaAlO) phase, however in each case, these phases would have to be exhibiting strong preferential texturing, as other major peaks are absent in the pattern. These three phases are commonly observed in this materials system during annealing, as was shown by in situ neutron diffraction. 7

8 Figure S9. (a) Temperature profile during annealing of LLZO ALD film inside a sealed in situ annealing furnace at the synchrotron beamline while flowing helium to maintain an inert atmosphere. (b) Area detector data showing evolution of the crystalline phases during annealing. The scans shown as columns in b correspond to the temperatures that (are directly above them in the temperature profile. (c) Integrated patterns from selected scans from (b). The bright area at the bottom of the area detector data when at elevated temperature is due to the single crystal substrate peak which appears at slightly higher 2θ. 8

9 Figure S10. Area Detector data from ALD film annealed in situ in He environment at 555 C with LiMnO 2 as a Li source to prevent Li loss. The spottiness of many of the peaks indicates a relatively small number of grains sampled, and means that peak ratios may not be statistically meaningful to determine preferential texture within the ALD film. The horizontal axis of the area detector is linear in 2θ, but not in d, so the plot above does not match perfectly, but the intensity and order of the peaks does match. Table S1. For each precursor used, the source temperature, pulse and purge times, growth rate, and number of subcycles in each supercycle. *Carrier gas flow rate increased to 20SCCM during purge step. 9

10 ICSD (c-llzo) Experimental Results ICSD (t-llzo) Experimental Results Figure S11. Synchrotron XRD patterns for annealed ALD films demonstrating nearly pure phase cubic (a) and tetragonal (b) LLZO. Patterns were fit to powder standards using MDI Jade software, allowing for temperature and preferred orientation effects. Nearly all of the peaks in both patterns are fit by the respective standards, indicating high purity. The remaining peaks in the cubic pattern were not successfully fit by any of the common impurities seen in this materials system without strong preferred orientation effects. Choppiness and noise observed at larger 2θ angles in (a) is an artifact resulting from area detector integration. 10

Supplementary Information for A Shortcut to Garnet-type Fast Li-Ion Conductors for All Solid State Batteries

Electronic Supplementary Material (ESI) for Journal of Materials Chemistry A. This journal is The Royal Society of Chemistry 2015 Supplementary Information for A Shortcut to Garnet-type Fast Li-Ion Conductors