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16. Nanoscale Chemical and Structural Analysis during In SituScanning/Transmission Electron Microscopy in Liquids

Author

Serra-Maia, Rui, Kumar, Pawan, Meng, Andrew C., Foucher, Alexandre C., Kang, Yijin, Karki, Khim, Jariwala, Deep, and Stach, Eric A.

Abstract

Liquid-cell scanning/transmission electron microscopy (S/TEM) has impacted our understanding of multiple areas of science, most notably nanostructure nucleation and growth and electrochemistry and corrosion. In the case of electrochemistry, the incorporation of electrodes requires the use of silicon nitride membranes to confine the liquid. The combined thickness of the liquid layer and the confining membranes prevents routine atomic-resolution characterization. Here, we show that by performing electrochemical water splitting in situto generate a gas bubble, we can reduce the thickness of the liquid to a film approximately 30 nm thick that remains covering the sample. The reduced thickness of the liquid allows the acquisition of atomic-scale S/TEM images with chemical and valence analysis through electron energy loss spectroscopy (EELS) and structural analysis through selected area electron diffraction (SAED). This contrasts with a specimen cell entirely filled with liquid, where the broad plasmon peak from the liquid obscures the EELS signal from the sample and induces beam incoherence that impedes SAED analysis. The gas bubble generation is fully reversible, which allows alternating between a full cell and thin-film condition to obtain optimal experimental and analytical conditions, respectively. The methodology developed here can be applied to other scientific techniques, such as X-ray scattering, Raman spectroscopy, and X-ray photoelectron spectroscopy, allowing for a multi-modal, nanoscale understanding of solid-state samples in liquid media.

Published
2021
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24. Molybdenum Substituted Vanadyl Phosphate ε-VOPO4 with Enhanced Two-Electron Transfer Reversibility and Kinetics for Lithium-Ion Batteries

Author

Wen, Bohua, primary, Wang, Qi, additional, Lin, Yuhchieh, additional, Chernova, Natasha A., additional, Karki, Khim, additional, Chung, Youngmin, additional, Omenya, Fredrick, additional, Sallis, Shawn, additional, Piper, Louis F. J., additional, Ong, Shyue Ping, additional, and Whittingham, M. S., additional

Published
2016
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25. Thermodynamics, Kinetics and Structural Evolution of ε-LiVOPO4 over Multiple Lithium Intercalation

Author

Lin, Yuh-Chieh, primary, Wen, Bohua, additional, Wiaderek, Kamila M., additional, Sallis, Shawn, additional, Liu, Hao, additional, Lapidus, Saul H., additional, Borkiewicz, Olaf J., additional, Quackenbush, Nicholas F., additional, Chernova, Natasha A., additional, Karki, Khim, additional, Omenya, Fredrick, additional, Chupas, Peter J., additional, Piper, Louis F. J., additional, Whittingham, M. Stanley, additional, Chapman, Karena W., additional, and Ong, Shyue Ping, additional

Published
2016
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29. Molybdenum Substituted Vanadyl Phosphate ε-VOPO4 with Enhanced Two-Electron Transfer Reversibility and Kinetics for Lithium-Ion Batteries

Author

Wen, Bohua, primary, Wang, Qi, additional, Lin, Yuh-Chieh, additional, Chernova, Natasha, additional, Karki, Khim, additional, Chung, Youngmin, additional, Omenya, Fredrick, additional, Sallis, Shawn, additional, Piper, Louis F.J., additional, Ong, Shyue Ping, additional, and Whittingham, M. Stanley, additional

Published
2015
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31. Structure Evolution and Thermal Stability of High-Energy-Density Li-Ion Battery Cathode Li2VO2F.

Author

Xiaoya Wang, Yiqing Huang, Dongsheng Ji, Omenya, Fredrick, Karki, Khim, Sallis, Shawn, Piper, Louis F. J., Wiaderek, Kamila M., Chapman, Karena W., Chernova, Natasha A., and Whittingham, M. Stanley

Subjects
THERMAL stability, ENERGY density, LITHIUM-ion batteries
Abstract

Lithium-ion batteries (LIBs) provide high-energy-density electrochemical energy storage, which plays a central role in advancing technologies ranging from portable electronics to electric vehicles (EVs). However, a demand for lighter, more compact devices and for extended range EVs continues to fuel the need for higher energy density storage systems. Li2VO2F, which is synthesized in its lithiated state, allows two-electron transfer per formula during the electrochemical reaction providing a high theoretical capacity of 462 mAh/g. Herein, the synthesis and electrochemical performance of Li2VO2F are optimized. The thermal stability of Li2VO2F, which is related to the safety of a battery is studied by thermal gravimetric analysis. The structure and vanadium oxidation state evolution along Li cycling are studied by ex-situ X-ray diffraction and absorption techniques. It is shown that the rock-salt structure of pristine Li2VO2F is stable up to at least 250°C, and is preserved upon Li cycling, which proceeds by the solid-solution mechanism. However, not all Li can be removed from the structure upon charge to 4.5 V, limiting the experimentally obtained capacity. [ABSTRACT FROM AUTHOR]

Published
2017
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32. REAL-TIME INVESTIGATION OF INDIVIDUAL SILICON NANOSTRUCTURED ELECTRODES FOR LITHIUM-ION BATTERIES

Author

Karki, Khim Bahadur and Karki, Khim Bahadur

Abstract

Silicon-based anode materials are an attractive candidate to replace today's widely-utilized graphitic electrodes for lithium-ion batteries because of their high gravimetric energy density (3572 mAh/g vs. 372 mAh/g for carbon) and relatively low working potential (~ 0.5V vs. Li/Li+). However, their commercial realization is still far away because of the structural instabilities associated with huge volume changes of ~300% during charge-discharge cycles. Recently, it has been proposed that silicon nanowires and other related one-dimensional nanostructures could be used as lithium storage materials with greatly enhanced storage capacities over that for graphite in the next generation of lithium-ion batteries. However, the studies to date have shown that the nanomaterials, while better, are still not good enough to withstand a large number of lithiation cycles, and moreover, there is little fundamental insight into the science of the improvements or the steps remaining before widespread adoption. This dissertation seeks to understand the basic structural properties and reaction kinetics of one dimensional silicon nanomaterials, including Si-C heterostructures during electrochemical lithiation/delithiation using in-situ transmission electron microscopy (TEM). I present my work in three parts. In part I, I lay out the importance of lithium-ion batteries and silicon-based anodes, followed by experimental techniques using in-situ TEM. In part II, I present results studied on three different nanostructures: Si nanowires (SiNWs), Si-C heterostructures and Si nanotubes (SiNTs). In SiNWs, we report an unexpected two-phase transformation and anisotropic volume expansion during lithiation. We also report an electrochemically-induced weld of ~200 MPa at the Si-Si interface. Next, studies on CNT@α-Si heterostructures with uniform and beaded-string structures with chemically tailored carbon-silicon interfaces are presented. In-situ TEM studies reveal that beaded-string CNT@ &#

Published
2013

33. Hoop-Strong Nanotubes for Battery Electrodes

Author

Karki, Khim, primary, Zhu, Yujie, additional, Liu, Yihang, additional, Sun, Chuan-Fu, additional, Hu, Liangbing, additional, Wang, YuHuang, additional, Wang, Chunsheng, additional, and Cumings, John, additional

Published
2013
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34. A Beaded-String Silicon Anode

Author

Sun, Chuan-Fu, primary, Karki, Khim, additional, Jia, Zheng, additional, Liao, Hongwei, additional, Zhang, Yin, additional, Li, Teng, additional, Qi, Yue, additional, Cumings, John, additional, Rubloff, Gary W., additional, and Wang, YuHuang, additional

Published
2013
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37. Electrolyte Stability Determines Scaling Limits for Solid-State 3D Li Ion Batteries

Author

Ruzmetov, Dmitry, primary, Oleshko, Vladimir P., additional, Haney, Paul M., additional, Lezec, Henri J., additional, Karki, Khim, additional, Baloch, Kamal H., additional, Agrawal, Amit K., additional, Davydov, Albert V., additional, Krylyuk, Sergiy, additional, Liu, Yang, additional, Huang, JianY., additional, Tanase, Mihaela, additional, Cumings, John, additional, and Talin, A. Alec, additional

Published
2011
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39. Anisotropic Swelling and Fracture of Silicon Nanowires during Lithiation

Author

Liu, Xiao Hua, primary, Zheng, He, additional, Zhong, Li, additional, Huang, Shan, additional, Karki, Khim, additional, Zhang, Li Qiang, additional, Liu, Yang, additional, Kushima, Akihiro, additional, Liang, Wen Tao, additional, Wang, Jiang Wei, additional, Cho, Jeong-Hyun, additional, Epstein, Eric, additional, Dayeh, Shadi A., additional, Picraux, S. Tom, additional, Zhu, Ting, additional, Li, Ju, additional, Sullivan, John P., additional, Cumings, John, additional, Wang, Chunsheng, additional, Mao, Scott X., additional, Ye, Zhi Zhen, additional, Zhang, Sulin, additional, and Huang, Jian Yu, additional

Published
2011
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40. Atomic Insight into the Layered/Spinel Phase Transformation in Charged LiNi0.80Co0.15Al0.05O2Cathode Particles

Author

Zhang, Hanlei, Karki, Khim, Huang, Yiqing, Whittingham, M. Stanley, Stach, Eric A., and Zhou, Guangwen

Abstract

Layered LiNi0.80Co0.15Al0.05O2(NCA) holds great promise as a potential cathode material for high energy density lithium ion batteries. However, its high capacity is heavily dependent on the stability of its layered structure, which suffers from a severe structure degradation resulting from a not fully understood layered → spinel phase transformation. Using high-resolution transmission electron microscopy and electron diffraction, we probe the atomic structure evolution induced by the layered → spinel phase transformation in the NCA cathode. We show that the phase transformation results in the development of a particle structure with the formation of complete spinel, spinel domains, and intermediate spinel from the surface to the subsurface region. The lattice planes of the complete and intermediate spinel phases are highly interwoven in the subsurface region. The layered → spinel transformation occurs via the migration of transition metal (TM) atoms from the TM layer into the lithium layer. Incomplete migration leads to the formation of the intermediate spinel phase, which is featured by tetrahedral occupancy of TM cations in the lithium layer. The crystallographic structure of the intermediate spinel is discussed and verified by the simulation of electron diffraction patterns.

Published
2017
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41. Tuning the Activity of Oxygen in LiNi0.8Co0.15Al0.05O2Battery Electrodes

Author

Karki, Khim, Huang, Yiqing, Hwang, Sooyeon, Gamalski, Andrew D., Whittingham, M. Stanley, Zhou, Guangwen, and Stach, Eric A.

Abstract

Layered transition metal oxides such as LiNi0.8Co 0.15Al0.05O2(NCA) are highly desirable battery electrodes. However, these materials suffer from thermal runaway caused by deleterious oxygen loss and surface phase transitions when in highly overcharged and overheated conditions, prompting serious safety concerns. Using in situ environmental transmission electron microscopy techniques, we demonstrate that surface oxygen loss and structural changes in the highly overcharged NCA particles are suppressed by exposing them to an oxygen-rich environment. The onset temperature for the loss of oxygen from the electrode particle is delayed to 350 °C at oxygen gas overpressure of 400 mTorr. Similar heating of the particles in a reducing hydrogen gas demonstrated a quick onset of oxygen loss at 150 °C and rapid surface degradation of the particles. The results reported here illustrate the fundamental mechanism governing the failure processes of electrode particles and highlight possible strategies to circumvent such issues.

Published
2016
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46. Tuning the Activity of Oxygen in LiNi 0.8 Co 0.15 Al 0.05 O 2 Battery Electrodes.

Author

Karki K, Huang Y, Hwang S, Gamalski AD, Whittingham MS, Zhou G, and Stach EA

Abstract

Layered transition metal oxides such as LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) are highly desirable battery electrodes. However, these materials suffer from thermal runaway caused by deleterious oxygen loss and surface phase transitions when in highly overcharged and overheated conditions, prompting serious safety concerns. Using in situ environmental transmission electron microscopy techniques, we demonstrate that surface oxygen loss and structural changes in the highly overcharged NCA particles are suppressed by exposing them to an oxygen-rich environment. The onset temperature for the loss of oxygen from the electrode particle is delayed to 350 °C at oxygen gas overpressure of 400 mTorr. Similar heating of the particles in a reducing hydrogen gas demonstrated a quick onset of oxygen loss at 150 °C and rapid surface degradation of the particles. The results reported here illustrate the fundamental mechanism governing the failure processes of electrode particles and highlight possible strategies to circumvent such issues.

Published
2016
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47. Electrolyte stability determines scaling limits for solid-state 3D Li ion batteries.

Author

Ruzmetov D, Oleshko VP, Haney PM, Lezec HJ, Karki K, Baloch KH, Agrawal AK, Davydov AV, Krylyuk S, Liu Y, Huang J, Tanase M, Cumings J, and Talin AA

Subjects
Energy Transfer, Equipment Design, Equipment Failure Analysis, Particle Size, Electric Power Supplies, Electrolytes chemistry, Lithium chemistry, Nanostructures chemistry, Nanostructures ultrastructure, Nanotechnology instrumentation
Abstract

Rechargeable, all-solid-state Li ion batteries (LIBs) with high specific capacity and small footprint are highly desirable to power an emerging class of miniature, autonomous microsystems that operate without a hardwire for power or communications. A variety of three-dimensional (3D) LIB architectures that maximize areal energy density has been proposed to address this need. The success of all of these designs depends on an ultrathin, conformal electrolyte layer to electrically isolate the anode and cathode while allowing Li ions to pass through. However, we find that a substantial reduction in the electrolyte thickness, into the nanometer regime, can lead to rapid self-discharge of the battery even when the electrolyte layer is conformal and pinhole free. We demonstrate this by fabricating individual, solid-state nanowire core-multishell LIBs (NWLIBs) and cycling these inside a transmission electron microscope. For nanobatteries with the thinnest electrolyte, ≈110 nm, we observe rapid self-discharge, along with void formation at the electrode/electrolyte interface, indicating electrical and chemical breakdown. With electrolyte thickness increased to 180 nm, the self-discharge rate is reduced substantially, and the NWLIBs maintain a potential above 2 V for over 2 h. Analysis of the nanobatteries' electrical characteristics reveals space-charge limited electronic conduction, which effectively shorts the anode and cathode electrodes directly through the electrolyte. Our study illustrates that, at these nanoscale dimensions, the increased electric field can lead to large electronic current in the electrolyte, effectively shorting the battery. The scaling of this phenomenon provides useful guidelines for the future design of 3D LIBs., (© 2011 American Chemical Society)

Published
2012
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