Silicon-Based Solid-State Batteries: Electrochemistry and Mechanics to Guide Design and Operation

Solid-state batteries (SSBs) are promising alternatives to the incumbent lithium-ion technology; however, they face a unique set of challenges that must be overcome to enable their widespread adoption. These challenges include solid-solid interfaces that are highly resistive, with slow kinetics, and a tendency to form interfacial voids causing diminished cycle life due to fracture and delamination. This modeling study probes the evolution of stresses at the solid electrolyte (SE) solid-solid interfaces, by linking the chemical and mechanical material properties to their electrochemical response, which can be used as a guide to optimize the design and manufacture of silicon (Si) based SSBs. A thin-film solid-state battery consisting of an amorphous Si negative electrode (NE) is studied, which exerts compressive stress on the SE, caused by the lithiation-induced expansion of the Si. By using a 2D chemo-mechanical model, continuum scale simulations are used to probe the effect of applied pressure and C-rate on the stress-strain response of the cell and their impacts on the overall cell capacity. A complex concentration gradient is generated within the Si electrode due to slow diffusion of Li through Si, which leads to localized strains. To reduce the interfacial stress and strain at 100% SOC, operation at moderate C-rates with low applied pressure is desirable. Alternatively, the mechanical properties of the SE could be tailored to optimize cell performance. To reduce Si stress, a SE with a moderate Young's modulus similar to that of lithium phosphorous oxynitride (∼77 GPa) with a low yield strength comparable to sulfides (∼0.67 GPa) should be selected. However, if the reduction in SE stress is of greater concern, then a compliant Young's modulus (∼29 GPa) with a moderate yield strength (1-3 GPa) should be targeted. This study emphasizes the need for SE material selection and the consideration of other cell components in order to optimize the performance of thin film solid-state batteries

A Search for Radio Gravitational Lenses, Using the Sloan Digital Sky Survey and the Very Large Array

We report on a novel search for radio gravitational lenses. Using the Very Large Array, we imaged ten candidates with both dual redshifts in Sloan Digital Sky Survey spectra and 1.4 GHz radio flux >2 mJy in the FIRST survey. The VLA maps show that in each case the radio emission is associated with the foreground galaxy rather than being lensed emission from the background galaxy, although at least four of our targets are strong lenses at optical wavelengths. These SDSS dual-redshift systems do not have lensed radio emission at the sensitivity of current radio surveys.Comment: 7 pages, 10 figures, uses emulateapj. Accepted to ApJ (11/25/2005). v2: Minor changes in accepted versio

Numerical Design of Microporous Carbon Binder Domains Phase in Composite Cathodes for Lithium-Ion Batteries

Lithium-ion battery (LIB) performance can be significantly affected by the nature of the complex electrode microstructure. The carbon binder domain (CBD) present in almost all LIB electrodes is used to enhance mechanical stability and facilitate electronic conduction, and understanding the CBD phase microstructure and how it affects the complex coupled transport processes is crucial to LIB performance optimization. In this work, the influence of microporosity in the CBD phase has been studied in detail for the first time, enabling insight into the relationships between the CBD microstructure and the battery performance. To investigate the effect of the CBD pore size distributions, a random field method is used to generate in silico a multiple-phase electrode structure, including bimodal pore size distributions seen in practice and microporous CBD with a tunable pore size and variable transport properties. The distribution of macropores and the microporous CBD phase substantially affected simulated battery performance, where battery specific capacity improved as the microporosity of the CBD phase increased

VLBA Imaging of the OH Maser in IIIZw35

We present a parsec-scale image of the OH maser in the nucleus of the active galaxy IIIZw35, made using the Very Long Baseline Array at a wavelength of 18 cm. We detected two distinct components, with a projected separation of 50 pc (for D=110 Mpc) and a separation in Doppler velocity of 70 km/s, which contain 50% of the total maser flux. Velocity gradients within these components could indicate rotation of clouds with binding mass densities of ~7000 solar masses per cubic parsec, or total masses of more than 500,000 solar masses. Emission in the 1665-MHz OH line is roughly coincident in position with that in the 1667-MHz line, although the lines peak at different Doppler velocities. We detected no 18 cm continuum emission; our upper limit implies a peak apparent optical depth greater than 3.4, assuming the maser is an unsaturated amplifier of continuum radiation.Comment: 10 pages, 3 figure

Towards Optimised Cell Design of Thin Film Silicon-Based Solid-State Batteries via Modelling and Experimental Characterisation

To realise the promise of solid-state batteries, negative electrode materials exhibiting large volumetric expansions, such as Li and Si, must be used. These volume changes can cause significant mechanical stresses and strains that affect cell performance and durability, however their role and nature in SSBs are poorly understood. Here, a 2D electro-chemo-mechanical model is constructed and experimentally validated using steady-state, transient and pulsed electrochemical methods. The model geometry is taken as a representative cross-section of a non-porous, thin-film solid-state battery with an amorphous Si (a-Si) negative electrode, lithium phosphorous oxynitride (LiPON) solid electrolyte and LiCoO2 (LCO) positive electrode. A viscoplastic model is used to predict the build-up of strains and plastic deformation of a-Si as a result of (de)lithiation during cycling. A suite of electrochemical tests, including electrochemical impedance spectroscopy, the galvanostatic intermittent titration technique and hybrid pulse power characterisation are carried out to establish key parameters for model validation. The validated model is used to explore the peak interfacial (a-Si∣LiPON) stress and strain as a function of the relative electrode thickness (up to a factor of 4), revealing a peak volumetric expansion from 69% to 104% during cycling at 1C. The validation of this electro-chemo-mechanical model under load and pulsed operating conditions will aid in the cell design and optimisation of solid-state battery technologies

Direct observations of electrochemically induced intergranular cracking in polycrystalline NMC811 particles

Establishing the nature of crack generation, formation, and propagation is paramount to understanding the degradation modes that govern decline in battery performance. Cracking has several possible origins; however, it can be classified in two general cases: mechanically induced, during manufacturing, or electrochemically induced, during operation. Accurate and repeatable tracking of operational cracking to sequentially image the same material as it undergoes cracking is highly challenging; observing these features requires the highest resolutions possible for 3D imaging techniques, necessitating very small sample geometry, while also achieving realistic electrochemical performance. Here, we present a technique in which particle cracking can be completely attributed to electrochemical stimulation via sequential ex situ imaging in a laboratory X-ray nano computed tomography (CT) instrument. This technique preserves the mechanical and electrochemical response of each particle without inducing damage in the particles except for the effects of high voltage. Significant cracking within the core of secondary particles was observed upon the electrochemical delithiation of NMC811, which propagated radially. As X-ray computed tomography allows for imaging of the particle cores, the particles were not required to be modified/milled, guaranteeing any synthesis induced strain in the particles was maintained during the whole technique, resulting in an observation that contrasts crystallographic data, suggesting a significant volume expansion of the secondary particles

Applications of advanced metrology for understanding the effects of drying temperature in the lithium-ion battery electrode manufacturing process

The performance of lithium-ion batteries is determined by the architecture and properties of electrodes formed during manufacturing, particularly in the drying process when solvent is removed and the electrode structure is formed. Temperature is one of the most dominant parameters that influences the process, and therefore a comparison of temperature effects on both NMC622-based cathodes (PVDF-based binder) and graphite-based anodes (water-based binder) dried at RT, 60, 80, 100 and 120 °C has been undertaken. X-ray computed tomography showed that NMC622 particles concentrated at the surface of the cathode coating except when dried at 60 °C. However, anodes showed similar graphite distributions at all temperatures. The discharge capacities for the cathodes dried at 60, 80, 100 and 120 °C displayed the following trend: 60 °C < 80 °C < 100 °C < 120 °C as C-rate was increased which was consistent with the trends found in adhesion testing between 60 and 120 °C. Focused-ion beam scanning electrode microscopy and energy-dispersive X-ray spectroscopy suggested that the F-rich binder distribution was largely insensitive to temperature for cathodes. In contrast, conductivity enhancing fine carbon agglomerated on the upper surface of the active NMC particles in the cathode as temperature increased. The cathode dried at RT had the highest adhesion force of 0.015 N mm−1 and the best electrochemical rate performance. Conversely, drying temperature had no significant effect on the electrochemical performance of the anode, which was consistent with only a relatively small change in the adhesion, related to the use of lower adhesion water-based binders

US Cosmic Visions: New Ideas in Dark Matter 2017: Community Report

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017.Comment: 102 pages + reference