ZnO additions to BaTiO 3 have been studied in order to determine the role of this dopant on sintering and microstructure development. As a consequence of a better initial dopant distribution, samples doped with 0.1 wt% zinc stearate show homogeneous fine-grained microstructure, while a doping level of 0.5 wt% solid ZnO is necessary to reach the same effect. When solid ZnO is used as the dopant precursor, ZnO is redistributed among the BaTiO 3 particles during heating. Since no liquid formation has been detected for temperatures below 1400°C in the system BaTiO 3 -ZnO, it is proposed that dopant redistribution takes place by vapor-phase transport and grain boundary diffusion. Shrinkage and porosimetry measurements have shown that grain growth is inhibited during the first step of sintering for the doped samples. STEM-EDX analysis revealed that solid solubility of ZnO into the BaTiO 3 lattice is very low, being strongly segregated at the grain boundaries. Grain growth control is attributed to a decrease in grain boundary mobility due to solute drag. Because of its effectiveness in controlling grain growth, ZnO appears to be an attractive additive for BaTiO 3 dielectrics.
Today, the electrical power supplies pose increasingly stringent requirements on battery package, for example, ultrafast vehicles charging algorithms and high current power supplies. To enable the optimal combination of energy and power capability, it is essential to understand kinetic barriers at all applicable length scales and time scales. On the length scale, we developed single electrode particles of ~25 µm size of a few nAh and adopted it to zoom in the transport of the molecules within the solid|liquid interface, excluding the complicated factors from typical composite electrode microstructures. The particle level electrodynamic measurements conducted in varied electrolyte compositions, reveal the anion group effects in charge transport, which leads to a significantly higher materials utilization during fast charge/discharge in both the single-particle measurements and on macroscopic composite electrodes. Furthermore, molecular dynamics (MD) simulations identify the preferred solvation structures of the liquid electrolytes, and density functional theory (DFT) calculations of their binding energies reveal the origin of the anion group effect. The anion dependence and the solvation lead to the fast kinetics at the interface. On the time scale, we probed the ultrafast transport algorithm with high-frequency modulation. A modulated DC pulse charging and discharging with high-frequency waveforms (up to ~ MHz) are performed to investigate the interfacial transport. This study reveals a possible mechanism by which ion transport kinetics in a lithium-ion battery are responsive to megahertz frequency excitation. Such algorithms are aiming to improve active material utilization as well as cycle life dramatically. This work was supported as part of the NorthEast Center for Chemical Energy Storage (NECCES), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under Award # DESC0012583.
In this Backstory, Yet-Ming Chiang and colleagues explain how their cost-focused approach led to the discovery of an affordable battery technology based on readily available materials. The ProblemCan batteries ever reach the cost of pumped hydroelectric storage, which today constitutes more than 99% of the deployed energy storage in the world, but has limited growth potential due to its geographical and environmental constraints? This was the overarching question that motivated our project team, which had a 5-year mandate from the U.S. Department of Energy's Joint Center for Energy Storage Research (JCESR) to answer such challenges. If achieved, such storage could scale in a way that allows intermittent renewable generation (wind and solar) to truly compete with fossil fuel-based electricity generation. Of JCESR's audacious goals captured by their motto ''5-5-5'' (meaning 5 times reduction in cost, 5 times increase in energy density, accomplished in 5 years), for grid storage the authors considered the cost challenge to be the most important by far, since almost any electrochemical approach would have a hundred times or higher energy density compared to pumped hydro. Energy density was mainly important insofar as it enabled more compact systems of lower cost. Thus, we obsessed about the cost-per-stored-energy metric, US$/kWh, although other attributes such as lifetime, safety, and toxicity of components would naturally also be important.
This research program investigates the properties of grain boundaries in complex multicomponent or nonstoichiometric oxides, including those of interest for electroceramics applications. One area of current research is the relationship between complex lattice defect structures and the ionic space charge at grain boundaries. We focus on TiO2 as a system with lattice defect properties characteristic of many electroceramics, including nonstoichiometry and regimes of high electronic conductivity. Model experiments are performed using a newly developed STEM method to quar, ify the grain boundary accumulation of trivalent (Al3+, Ga3+) and pentavalent (Nb5+) cation dopants. A space charge model is developed which explicitly includes the lattice defect chemistry of TiO2. This work is aimed at making for the first time a detailed, quantitative comparison between space charge theory and grain boundary segregation. The fundamental defect formation energies at grain boundaries and their variation from boundary to boundary are studied. In future work, space charge effects at nanocrystalline grain sizes, and at bimaterial interfaces, emphasizing crystal-glass interfaces germane to the behavior of thin glassy films at grain boundaries, are to be studied. A second area of research concerns the direct measurement of grain boundary thermodynamic properties and size-dependent segregation and transport phenomena in nanocrystaUine oxides. Current efforts are aimed at using high temperature calorimetry to measure the heat of grain coarsening and excess heat capacity of nanocrystalline TiO2, in order to obtain the specific grain boundary enthalpy and entropy and their temperature and composition dependences. With appropriate models for the enthalpy release rate during grain coarsening, in-situ measurement of grain growth kinetic parameters (time exponent, activation energies) is possible. The effect of solute segregation on grain boundary thermodynamic and kinetic properties, and size-dependent segregation phenomena, including the effects of space charge fields on grain growth and superplastic deformation, are to be studied.
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