Carbon thin film thermometry

The work concerning carbon thin film thermometry is reported. Optimum film deposition parameters were sought on an empirical basis for maximum stability of the films. One hundred films were fabricated for use at the Marshall Space Flight Center; 10 of these films were given a precise quasi-continuous calibration of temperature vs. resistance with 22 intervals between 5 and 80 K using primary platinum and germanium thermometers. Sensitivity curves were established and the remaining 90 films were given a three point calibration and fitted to the established sensitivity curves. Hydrogen gas-liquid discrimination set points are given for each film

The cost and economic features of a reduction in grade on the X division of the Y.Z. railroad

Thesis (B.S.)--University of Illinois, 1910.Typescript.Includes bibliographical references

Unraveling the Complex Delithiation Mechanisms of Olivine-Type Cathode Materials, LiFe<inf>x</inf>Co<inf>1-x</inf>PO<inf>4</inf>

The delithiation mechanisms occurring within the olivine-type class of cathode materials for Li-ion batteries have received considerable attention owing to the good capacity retention at high rates for LiFePO4. A comprehensive mechanistic study of the (de)lithiation reactions that occur when the substituted olivine-type cathode materials LiFexCo1-xPO4 (x = 0, 0.05, 0.125, 0.25, 0.5, 0.75, 0.875, 0.95 and 1) are electrochemically cycled is reported here, using in situ X-ray diffraction (XRD) data, and supporting ex situ 31P NMR spectra. On the first charge, two intermediate phases are observed and identified: Li1-x(Fe3+)x(Co2+)1-xPO4 for 0 Fe3+) and Li2/3FexCo1-xPO4 for 0 ≤ x ≤ 0.5 (i.e. the Co-majority materials). For the Fe-rich materials, we study how nonequilibrium, single-phase mechanisms that occur discretely in single particles, as observed for LiFePO4 at high rates, are affected by Co substitution. In the Co-majority materials, a two-phase mechanism with a coherent interface is observed, as was seen in LiCoPO4, and we discuss how it is manifested in the XRD patterns. We then compare the nonequilibrium, single-phase mechanism with the bulk single-phase and the coherent interface two-phase mechanisms. Despite the apparent differences between these mechanisms, we discuss how they are related and interconverted as a function of Fe/Co substitution and the potential implications for the electrochemistry of this system.This is the final version of the article. It first appeared from The American Chemical Society via https://doi.org/10.1021/acs.chemmater.6b0031

Mapping the inhomogeneous electrochemical reaction through porous LiFePO&lt;inf&gt;4&lt;/inf&gt;-electrodes in a standard coin cell battery

[Image - see article] Nanosized, carbon-coated LiFePO4 (LFP) is a promising cathode for Li-ion batteries. However, nano-particles are problematic for electrode design, optimized electrodes requiring high tap densities, good electronic wiring, and a low tortuosity for efficient Li diffusion in the electrolyte in between the solid particles, conditions that are difficult to achieve simultaneously. Using in situ energy-dispersive X-ray diffraction, we map the evolution of the inhomogeneous electrochemical reaction in LFP-electrodes. On the first cycle, the dynamics are limited by Li diffusion in the electrolyte at a cycle rate of C/7. On the second cycle, there appear to be two rate-limiting processes: Li diffusion in the electrolyte and electronic conductivity through the electrode. Three-dimensional modeling based on porous electrode theory shows that this change in dynamics can be reproduced by reducing the electronic conductivity of the composite electrode by a factor of 8 compared to the first cycle. The poorer electronic wiring could result from the expansion and contraction of the particles upon cycling and/or the formation of a solid-electrolyte interphase layer. A lag was also observed perpendicular to the direction of the current: the LFP particles at the edges of the cathode reacted preferentially to those in the middle, owing to the closer proximity to the electrolyte source. Simulations show that, at low charge rates, the reaction becomes more uniformly distributed across the electrode as the porosity or the width of the particle-size distribution is increased. However, at higher rates, the reaction becomes less uniform and independent of the particle-size distribution.We acknowledge the Engineering Physical Science Research Council (EPSRC) for a Doctoral Training Account Award (for FCS) and the US Department of Energy (DOE) for support via the NECCES, an Energy Frontier Research Center (DE-SC0001294 and DE-SC0012583). FCS acknowledges the Science and Technology Facilities Council for travel funding through the Global Challenge Network in Batteries and Electrochemical Energy Devices. Synchrotron X-ray beamtime was provided by Diamond Light Source, under experiment number EE8385. We also thank Zlatko Saracevic at the Department of Chemical Engineering at the University of Cambridge for help with the BET experiments and Jon Rickard at the Department of Physics at the University of Cambridge for help with the SEM. Lastly; we thank Charles Monroe and Paul Shearing for discussions on this project.This is the final version of the article. It first appeared from ACS Publications via http://dx.doi.org/10.1021/cm504317

Identifying the Structure of the Intermediate, Li2/3CoPO4, Formed during Electrochemical Cycling of LiCoPO4.

In situ synchrotron diffraction measurements and subsequent Rietveld refinements are used to show that the high energy density cathode material LiCoPO4 (space group Pnma) undergoes two distinct two-phase reactions upon charge and discharge, both occurring via an intermediate Li2/3(Co2+)2/3(Co3+)1/3PO4 phase. Two resonances are observed for Li2/3CoPO4 with intensity ratios of 2:1 and 1:1 in the 31P and 7Li NMR spectra, respectively. An ordering of Co2+/Co3+ oxidation states is proposed within a (a × 3b × c) supercell, and Li+/vacancy ordering is investigated using experimental NMR data in combination with first-principles solid-state DFT calculations. In the lowest energy configuration, both the Co3+ ions and Li vacancies are found to order along the b-axis. Two other low energy Li+/vacancy ordering schemes are found only 5 meV per formula unit higher in energy. All three configurations lie below the LiCoPO4-CoPO4 convex hull and they may be readily interconverted by Li+ hops along the b-direction.This is the final version. It was first published by ACS Publications at http://pubs.acs.org/doi/abs/10.1021/cm502680

Localized concentration reversal of lithium during intercalation into nanoparticles.

Nanoparticulate electrodes, such as Li x FePO4, have unique advantages over their microparticulate counterparts for the applications in Li-ion batteries because of the shortened diffusion path and access to nonequilibrium routes for fast Li incorporation, thus radically boosting power density of the electrodes. However, how Li intercalation occurs locally in a single nanoparticle of such materials remains unresolved because real-time observation at such a fine scale is still lacking. We report visualization of local Li intercalation via solid-solution transformation in individual Li x FePO4 nanoparticles, enabled by probing sub-angstrom changes in the lattice spacing in situ. The real-time observation reveals inhomogeneous intercalation, accompanied with an unexpected reversal of Li concentration at the nanometer scale. The origin of the reversal phenomenon is elucidated through phase-field simulations, and it is attributed to the presence of structurally different regions that have distinct chemical potential functions. The findings from this study provide a new perspective on the local intercalation dynamics in battery electrodes

Three-dimensional localization of nanoscale battery reactions using soft X-ray tomography.

Battery function is determined by the efficiency and reversibility of the electrochemical phase transformations at solid electrodes. The microscopic tools available to study the chemical states of matter with the required spatial resolution and chemical specificity are intrinsically limited when studying complex architectures by their reliance on two-dimensional projections of thick material. Here, we report the development of soft X-ray ptychographic tomography, which resolves chemical states in three dimensions at 11 nm spatial resolution. We study an ensemble of nano-plates of lithium iron phosphate extracted from a battery electrode at 50% state of charge. Using a set of nanoscale tomograms, we quantify the electrochemical state and resolve phase boundaries throughout the volume of individual nanoparticles. These observations reveal multiple reaction points, intra-particle heterogeneity, and size effects that highlight the importance of multi-dimensional analytical tools in providing novel insight to the design of the next generation of high-performance devices