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© 2018 National Academy of Sciences. All rights reserved. Solid-state ion shuttles are of broad interest in electrochemical devices, nonvolatile memory, neuromorphic computing, and bio-mimicry utilizing synthetic membranes. Traditional design approaches are primarily based on substitutional doping of dissimilar valent cations in a solid lattice, which has inherent limits on dopant concentration and thereby ionic conductivity. Here, we demonstrate perovskite nickelates as Li-ion shuttles with simultaneous suppression of electronic transport via Mott transition. Electrochemically lithiated SmNiO3 (Li-SNO) contains a large amount of mobile Li+ located in interstitial sites of the perovskite approaching one dopant ion per unit cell. A significant lattice expansion associated with interstitial doping allows for fast Li+ conduction with reduced activation energy. We further present a generalization of this approach with results on other rare-earth perovskite nickelates as well as dopants such as Na+. The results highlight the potential of quantum materials and emergent physics in design of ion conductors.

Copyright © 2018 American Chemical Society. All-solid-state batteries promise significant safety and energy density advantages over liquid-electrolyte batteries. The interface between the cathode and the solid electrolyte is an important contributor to charge transfer resistance. Strong bonding of solid oxide electrolytes and cathodes requires sintering at elevated temperatures. Knowledge of the temperature dependence of the composition and charge transfer properties of this interface is important for determining the ideal sintering conditions. To understand the interfacial decomposition processes and their onset temperatures, model systems of LiCoO2 (LCO) thin films deposited on cubic Al-doped Li7La3Zr2O12 (LLZO) pellets were studied as a function of temperature using interface-sensitive techniques. X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and energy-dispersive X-ray spectroscopy data indicated significant cation interdiffusion and structural changes starting at temperatures as low as 300 °C. La2Zr2O7 and Li2CO3 were identified as decomposition products after annealing at 500 °C by synchrotron X-ray diffraction. X-ray absorption spectroscopy results indicate the presence of also LaCoO3 in addition to La2Zr2O7 and Li2CO3. On the basis of electrochemical impedance spectroscopy and depth profiling of the Li distribution upon potentiostatic hold experiments on symmetric LCO|LLZO|LCO cells, the interfaces exhibited significantly increased impedance, up to 8 times that of the as-deposited samples after annealing at 500 °C. Our results indicate that lower-temperature processing conditions, shorter annealing time scales, and CO2-free environments are desirable for obtaining ceramic cathode|electrolyte interfaces that enable fast Li transfer and high capacity., Bosch Energy Research Network (BERN) grant, MISTI MIT-Imperial College grant, NSF (DMR 14-19807), DOE Office of Basic Energy Sciences (Contract No. DE-AC02-06CH11357), DOE Office of Science (Contract No. DE-SC0012704), U.S. DOE Contract (DE-AC02-05CH11231)

Chromium (Cr) poisoning is one of the main sources for the performance degradation of solid oxide fuel cells (SOFCs) during long-term operation. However, the mechanism of Cr poisoning-induced degradation can be extremely complicated, making accurate prediction of degradation rate very difficult. In this work, we present a new approach enabled by machine learning algorithms to predict the performance degradation of SOFC cathodes. Cathode materials based on SrFeO3 with different dopants, i.e., SrFe0.75M0.25O3-delta (M = Co, Fe, Mn, Mo, Nb, and Ni), were chosen as model systems to study the effect of dopant elements on the resistance to Cr poisoning. Electrochemical impedance spectroscopy (EIS) data were collected up to 96 hours for each composition, and were used as input for training the neural network and for validation. The predicted data at 156 hours match the experimental results well, implying the great prediction power of our machine-learning-assisted (MLA) method. Our work demonstrates that the MLA approach can significantly reduce the time needed for extracting the degradation rate of SOFC cathode materials.

© 2018 National Academy of Sciences. All rights reserved. Solid-state ion shuttles are of broad interest in electrochemical devices, nonvolatile memory, neuromorphic computing, and bio-mimicry utilizing synthetic membranes. Traditional design approaches are primarily based on substitutional doping of dissimilar valent cations in a solid lattice, which has inherent limits on dopant concentration and thereby ionic conductivity. Here, we demonstrate perovskite nickelates as Li-ion shuttles with simultaneous suppression of electronic transport via Mott transition. Electrochemically lithiated SmNiO3 (Li-SNO) contains a large amount of mobile Li+ located in interstitial sites of the perovskite approaching one dopant ion per unit cell. A significant lattice expansion associated with interstitial doping allows for fast Li+ conduction with reduced activation energy. We further present a generalization of this approach with results on other rare-earth perovskite nickelates as well as dopants such as Na+. The results highlight the potential of quantum materials and emergent physics in design of ion conductors.

© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Distinct properties of multiple phases of vanadium oxide (VOx) render this material family attractive for advanced electronic devices, catalysis, and energy storage. In this work, phase boundaries of VOx are crossed and distinct electronic properties are obtained by electrochemically tuning the oxygen content of VOx thin films under a wide range of temperatures. Reversible phase transitions between two adjacent VOx phases, VO2 and V2O5, are obtained. Cathodic biases trigger the phase transition from V2O5 to VO2, accompanied by disappearance of the wide band gap. The transformed phase is stable upon removal of the bias while reversible upon reversal of the electrochemical bias. The kinetics of the phase transition is monitored by tracking the time-dependent response of the X-ray absorption peaks upon the application of a sinusoidal electrical bias. The electrochemically controllable phase transition between VO2 and V2O5 demonstrates the ability to induce major changes in the electronic properties of VOx by spanning multiple structural phases. This concept is transferable to other multiphase oxides for electronic, magnetic, or electrochemical applications.

Copyright © 2018 American Chemical Society. All-solid-state batteries promise significant safety and energy density advantages over liquid-electrolyte batteries. The interface between the cathode and the solid electrolyte is an important contributor to charge transfer resistance. Strong bonding of solid oxide electrolytes and cathodes requires sintering at elevated temperatures. Knowledge of the temperature dependence of the composition and charge transfer properties of this interface is important for determining the ideal sintering conditions. To understand the interfacial decomposition processes and their onset temperatures, model systems of LiCoO2 (LCO) thin films deposited on cubic Al-doped Li7La3Zr2O12 (LLZO) pellets were studied as a function of temperature using interface-sensitive techniques. X-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and energy-dispersive X-ray spectroscopy data indicated significant cation interdiffusion and structural changes starting at temperatures as low as 300 °C. La2Zr2O7 and Li2CO3 were identified as decomposition products after annealing at 500 °C by synchrotron X-ray diffraction. X-ray absorption spectroscopy results indicate the presence of also LaCoO3 in addition to La2Zr2O7 and Li2CO3. On the basis of electrochemical impedance spectroscopy and depth profiling of the Li distribution upon potentiostatic hold experiments on symmetric LCO|LLZO|LCO cells, the interfaces exhibited significantly increased impedance, up to 8 times that of the as-deposited samples after annealing at 500 °C. Our results indicate that lower-temperature processing conditions, shorter annealing time scales, and CO2-free environments are desirable for obtaining ceramic cathode|electrolyte interfaces that enable fast Li transfer and high capacity.

Oxygen vacancies in complex oxides are indispensable for information and energy technologies. There are several means to create oxygen vacancies in bulk materials. However, the use of ionic interfaces to create oxygen vacancies has not been fully explored. Herein, we report an oxide nanobrush architecture designed to create high-density interfacial oxygen vacancies. An atomically well-defined (111) heterointerface between the fluorite CeO2 and the bixbyite Y2O3 is found to induce a charge modulation between Y3+ and Ce4+ ions enabled by the chemical valence mismatch between the two elements. Local structure and chemical analyses, along with theoretical calculations, suggest that more than 10% of oxygen atoms are spontaneously removed without deteriorating the lattice structure. Our fluorite–bixbyite nanobrush provides an excellent platform for the rational design of interfacial oxide architectures to precisely create, control, and transport oxygen vacancies critical for developing ionotronic and memristive devices for advanced energy and neuromorphic computing technologies., United States. Department of Energy. Office of Science User Facility (Contract DE-AC02-05CH11231), United States. Department of Energy. Office of Science (Contract DE-AC02-06CH11357)

Nanoscale complex-oxide thin films prepared by well-established growth techniques, such as pulsed-laser deposition or molecular-beam epitaxy, often exhibit compositions that deviate from the ideal stoichiometry. Even small variations in composition can lead to substantial changes in the technologically relevant electronic, magnetic, and optical properties of these materials. To assess the reasons behind this variability, and ultimately to allow tuning the properties of oxide films with precise control of the deposition parameters, high-resolution detection of the nonstoichiometry introduced during growth is needed. The resolution of current techniques, such as x-ray diffraction, fluorescence, or spectroscopy, is limited to estimating composition differences in the percent level, which is often insufficient for electronic-device quality. We develop an unconventional approach based on scanning tunneling microscopy for enabling the determination of cation imbalance introduced in thin films with exceptionally small detection limit. We take advantage of the well-controlled surface reconstructions on SrTiO3(110), and use the established relation between those reconstructions and the surface composition to assess the cation excess deposited in pulsed-laser grown SrTiO3(110) films. We demonstrate that a <0.1% change in cation nonstoichiometry is detectable by our approach. Furthermore, we show that, for thin films that accommodate all the nonstoichiometry at the surface, this method has no fundamental detection limit., NSF CAREER Award of the National Science Foundation, Division of Materials Research, Ceramics Program, Grant No. 1055583, U. S. National Science Foundation, Division of Materials Research (Grant no. 1419807)