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DePaul Discoveries DePaul Discoveries Volume 4 Issue 1 Article 10 2015 Eects of Temperature on the Crystal Structure of Lithium- E ects of Temperature on the Crystal Structure of Lithium- Lanthanum Zirconate Lanthanum Zirconate Mir Iqbal DePaul University, [email protected] Follow this and additional works at: https://via.library.depaul.edu/depaul-disc Part of the Condensed Matter Physics Commons Recommended Citation Recommended Citation Iqbal, Mir (2015) "Eects of Temperature on the Crystal Structure of Lithium-Lanthanum Zirconate," DePaul Discoveries: Vol. 4 : Iss. 1 , Article 10. Available at: https://via.library.depaul.edu/depaul-disc/vol4/iss1/10 This Article is brought to you for free and open access by the College of Science and Health at Via Sapientiae. It has been accepted for inclusion in DePaul Discoveries by an authorized editor of Via Sapientiae. For more information, please contact [email protected].

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Page 1: DePaul Discoveries

DePaul Discoveries DePaul Discoveries

Volume 4 Issue 1 Article 10

2015

Effects of Temperature on the Crystal Structure of Lithium-E ects of Temperature on the Crystal Structure of Lithium-

Lanthanum Zirconate Lanthanum Zirconate

Mir Iqbal DePaul University, [email protected]

Follow this and additional works at: https://via.library.depaul.edu/depaul-disc

Part of the Condensed Matter Physics Commons

Recommended Citation Recommended Citation Iqbal, Mir (2015) "Effects of Temperature on the Crystal Structure of Lithium-Lanthanum Zirconate," DePaul Discoveries: Vol. 4 : Iss. 1 , Article 10. Available at: https://via.library.depaul.edu/depaul-disc/vol4/iss1/10

This Article is brought to you for free and open access by the College of Science and Health at Via Sapientiae. It has been accepted for inclusion in DePaul Discoveries by an authorized editor of Via Sapientiae. For more information, please contact [email protected].

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Effects of Temperature on the Crystal Structure of Lithium-Lanthanum Zirconate E ects of Temperature on the Crystal Structure of Lithium-Lanthanum Zirconate

Acknowledgements Acknowledgements Faculty Advisor: Dr. Gabriela Gonzalez Aviles, Department of Physics Research completed Autumn 2014 Author contact: [email protected]

This article is available in DePaul Discoveries: https://via.library.depaul.edu/depaul-disc/vol4/iss1/10

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EFFECTS OF TEMPERATURE ON THE CRYSTAL STRUCTURE OF LITHIUM-LANTHANUM ZIRCONATE

Effects of Temperature on the Crystal Structure ofLithium-Lanthanum Zirconate

Mir IqbalDepartment of Physics

ABSTRACT Lithium-lanthanum zirconate (LLZ) can potentially be used as a solid electrolyte inlithium-metal batteries. Li-metal batteries offer superior charge capacities and higher energy densi-ties compared to currently used Li-ion batteries. Lithium is highly reactive, which can be dangerousin consumer electronics, but a layer of LLZ electrolyte inserted alongside the Li-metal electrodegreatly stabilizes its reactivity. The cubic phase structure of LLZ (Li7La3Zr2O12) has the highestconductivity of its crystalline phases, making it the most promising crystal form of LLZ for thisapplication. Samples of LLZ were doped with different amounts of aluminum and heated to hightemperatures in a furnace while measuring in-situ x-ray diffraction data. The aim of this project wasto calibrate and integrate the data. Preliminary results show that different crystallographic phasesform as the samples are heated. The amount of aluminum present plays a major role in stabilizingthe cubic phase.

1. INTRODUCTION

The past few decades have been marked by anever-increasing ubiquity of consumer electronicsin our world. As electronic devices continue tobecome more sophisticated, affordable, and in-dispensable to everyday life, research relating toelectronics technology is persistently driven bydemand for higher-performing electronic devices.In most cases, a crucial aspect of a device’s qual-ity is its battery performance.

Currently, commercial rechargeable batteriesare lithium-ion based. This technology offers high-energy density and charge capacity, and can bemass-produced within the necessary safety require-ments. These batteries most often use lithiated

Faculty Advisor: Dr. Gabriela Gonzalez Aviles, Depart-ment of PhysicsResearch completed Autumn 2014Author contact: [email protected]

graphite as their anode, meaning that the anodeis comprised of a graphite plating with lithiumdeposited onto it [1]. Generally, in lithium bat-teries, the more lithium an anode stores, the moreenergy the battery can output overall. So in prin-ciple, the ideal anode for such a battery wouldsimply be a lithium-metal anode. Li-metal elec-trodes boast a specific energy density several timeshigher than lithiated graphite.

Unfortunately, such Li-metal electrodes comewith a major complication. Because lithium isso reactive, over several charge-discharge cycles,the anode can start to form growths of branch-like structures called dendrites, which can even-tually span across to the cathode and cause acatastrophic short circuit or explosion. This isunacceptable for most applications where safetyis a priority, especially in consumer electronics.Due to this problem, development in Li-metalrechargeable batteries was largely abandoned bythe late 1980s [2].

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Iqbal: E?ects of Temperature on the Crystal Structure of LLZ

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EFFECTS OF TEMPERATURE ON THE CRYSTAL STRUCTURE OF LITHIUM-LANTHANUM ZIRCONATE

However, recent research has shown that cer-tain solid-electrolyte components can greatly re-duce the tendency for Li-metal anodes to formdendrites, and may allow the Li-metal battery tofunction safely and effectively in the long term.In particular, a candidate for this electrolyte islithium-lanthanum zirconate (Li7La3Zr2O12), alsoknown as LLZ.

The purpose of this project was to examine thebehavior of LLZ samples as they were subjectedto steadily increasing temperatures ranging fromroom temperature to 1000◦C. Observations re-garding what phases (crystal structure configura-tion) formed at various temperatures were partic-ularly relevant. Previous research has indicatedthat the phase structure most well-suited for thisapplication is the cubic structure, since it has thehighest conductivity of any LLZ phase. One ofthe main objectives of this project was to deter-mine what temperatures maximize the formationand stability of cubic LLZ in a sample.

2. METHODS

The starting samples consisted of LLZ precur-sors prepared by a sol-gel method [3]. Aluminumdopants were added in order to stabilize the cubicstructure. The doping amounts were 0%, 0.3%,0.5%, and 1%, by weight percent. Synchrotronx-ray diffraction data of these samples were mea-sured at Sector 1 of the Advanced Photon Source(APS) at Argonne National Laboratory (ANL).The data were collected in transmission geome-try, starting at room temperature up to 1000◦Cin static air or flowing helium gas using a two-dimensional detector. Above approximately 700◦C each sample began to fuse with its glass capil-lary, eliminating all cubic LLZ phase and render-ing the data irrelevant. Thus, only data below700 ◦C were analyzed. The incident x-ray beamhad an energy of 20.076 keV. Over the courseof this project, the raw data images were cal-ibrated, integrated, and analyzed with the Ri-etveld method to examine the crystalline phasecomposition and atomic structures of the samplethrough the heating cycle.

The data set taken at the APS was very large,with over 800 raw diffraction images to process

Figure 1. A glass capillaryfilled with LLZ powder is heldbetween two heating coils in thishigh-temperature cell configura-tion.

Figure 2. The experimentalsetup at the APS synchrotron.Here the sample is being heated.The detector is found behind thesample toward the left of the pic-ture.

and analyze. To effectively process this large col-lection of data, the analysis process was com-pleted in three main steps, using a different soft-ware program for each stage. First, GSAS-II,an open-source python program, was used to cal-ibrate and integrate the raw diffraction imagesinto one-dimensional intensity plots [4]. Next, aMATLAB script, developed in another student’sundergraduate research project, converted the re-sulting files into a format suitable for the finalstep. Finally, the FullProf suite was used to fitthe data with crystallographic models [5].

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The data images were calibrated using the 640cNIST silicon reference material [6]. The exactwavelength of the incident beam, the positionof the beam center at the detector, the sample-detector distances, and the tilt and rotation ofthe detector were determined. These parameterswere then stored and used by GSAS II to pre-cisely and accurately process and integrate all theimages.

As seen in Figures 3 and 4, the post holdingthe beam stop left a shadow in the data images.This was easily left out by selecting the appro-priate azimuthal range of values to be integratedover, such that the range containing the shadowof the post was not included. The other mainsource of undesirable data was the glass capil-lary itself. Its imprint was removed from thedata by taking a diffraction image of the emptycapillary. Then those data were subtracted fromeach image during integration (subject to somemultiplier factor), as seen in Figure 5. Find-ing this multiplier was somewhat difficult becausethe factor changed throughout the data set, andhad to be manually redetermined. Once this wasrectified, the images were integrated.

The GSAS-II output files were converted, us-ing a MATLAB script, into data files compatiblewith FullProf, the software used to obtain crys-tallographic information about the samples. Inorder to analyze the data, the FullProf Rietveldsoftware needed initial crystallographic informa-tion for the phases in the sample and other refine-ment parameters. FullProf used this informationto automatically and continuously optimize thefits of the crystal structure of the LLZ samplevia the Rietveld refinement method [7].

3. Results and Discussion

The resulting models can provide us with awealth of information (including unit cell size,atomic positions, and compositional distributionof the crystalline phases) about the crystal struc-ture of each sample throughout each heating step.Figure 6 is an example of a Rietveld refinementon a sample with 0.3% Al-dopant that containedmostly cubic LLZ. The complete Rietveld anal-ysis of the full data set is still in progress, butsome basic conclusions can be made at this stage.

Figure 3. A calibrated rawdata image ready to be inte-grated. The program can bemade to neglect extraneous datafrom the support post holdingthe beam stop by cutting out aslice from the area to be inte-grated over.

The temperatures at which the cubic phase ismost dominant varies between samples with dif-ferent aluminum doping levels. Aluminum is akey dopant that stabilizes the cubic phase. Theseresults can be used to decide the doping level andappropriate temperature that optimize the cubicphase. LLZ samples can be quickly cooled to pre-serve the phase composition in the optimal state.

4. Conclusion

This research analyzed x-ray synchrotron dataof lithium-lanthanum zirconate samples with dif-ferent aluminum doping levels, collected at hightemperatures. The raw two-dimensional diffrac-tion data were calibrated and integrated. Com-plete analysis of these data and refinement of themodels is ongoing. The data are being fittedto crystallographic models which provide muchmore detailed information about the crystal struc-ture of the LLZ sample as it undergoes heating.Preliminary results show that different crystallo-graphic phases form as the samples are heated.The amount of aluminum present plays a major

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EFFECTS OF TEMPERATURE ON THE CRYSTAL STRUCTURE OF LITHIUM-LANTHANUM ZIRCONATE

Figure 4. The diffraction im-age of the empty glass capillary.This broad, continuous ring isdue to the amorphous structureof the silica capillary and standsin contrast to the sharp, discreterings diffracted from the crys-talline LLZ. The capillary con-tribution to each image was sub-tracted.

Figure 5. The effect of back-ground subtraction. The blueplot is an intensity integrationwith the capillary data included,seen as a broad hump. The cap-illary data was subtracted in thegreen plot.

Figure 6. The experimentaldata from one image (in red) isfitted with the Rietveld method(in black). The green verticallines indicate the positions of fit-ted peaks, and the difference be-tween the fit and the data isshow in blue at the bottom.

role in stabilizing the cubic phase. Full analy-sis of these data may provide information aboutthe optimum heating conditions that maximizethe presence of the cubic LLZ phase. This infor-mation will be valuable to researchers studyingthis material for possible applications in next-generation battery technology.

5. ACKNOWLEDGEMENTS

I would like to thank the DePaul Physics De-partment, the College of Science and Health, andthe Undergraduate Summer Research Program,for granting me the funding and opportunity toparticipate in this research. I would like to thankNoah Wilson, who created the crucial MATLABdata conversion script I used. The samples weremade by Aude Hubaud and Brian Ingram at Ar-gonne National Laboratory. The data were col-lected at Sector 1 of the Advanced Photon Source,which is funded by the Office of Science, Officeof Basic Energy Sciences in the U.S. Departmentof Energy. Software packages GSAS-II, MAT-LAB, and the Fullprof Suite were used in thisproject. Lastly, I would like to sincerely thankDr. Gonzalez Aviles for her support and expert

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guidance throughout my involvement in this re-search project.

References

[1] M.M. Thackeray, J.O. Thomas and M.S. Whitting-ham, Science and Applications of Mixed Conductors

for Lithium Batteries, MRS Bulletin, 25 (2010), 39–

46.[2] K.J. Harry, D.T. Hallinan, D.Y. Parkinson, A.A.

MacDowell, and N.P. Balsara, Detection of subsur-

face structures underneath dendrites formed on cy-cled lithium metal electrodes, Nature Materials, 13

(2010), 69–73.[3] N. Janani, S. Ramakumar, L. Dhivya, C. Devian-

napoorani, K. Saranya, and Ramaswamy Murugan,

Synthesis of cubic Li7La3Zr2O12 by modified solgelprocess, Ionics, 17 (2011), 575-580.

[4] B.H. Toby, and R.B. Von Dreele, GSAS-II: the gen-

esis of a modern open-source all purpose crystallog-raphy software package, J. Appl. Cryst, 46 (2013),

544–549.

[5] J. Rodrıguez-Carvajal, FullProf Suite,http://www.ill.eu/sites/fullprof/index.html.

[6] National Institute of Standards and Technology,

Standard Reference Material 640c, Silicon PowderLine Position and Line Shape Standard for Powder

Diffraction, (2000).[7] H. M. Rietveld (1969). ”A profile refinement method

for nuclear and magnetic structures”. Journal of Ap-

plied Crystallography 2 (2): 6571.

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