A theory and a simulation capability for the growth of a solid electrolyte interphase layer at anode particles in lithium ion batteries

A major mechanism for electrochemical aging of Li-ion batteries is the formation of a solid electrolyte interphase (SEI) layer, which results in an impedance rise at the anode and also leads to capacity fade. The formation of an SEI layer consumes Li-ions and competes with the desired Li intercalation. Often, the cyclic volume changes – or “breathing” – of an anode particle during Li-ion intercalation and deintercalation can cause the SEI layer to delaminate from the surface of the particle, which causes new SEI to be formed on the newly exposed particle surface and this accelerates capacity fade. We have formulated a continuum theory for the formation and growth of an SEI layer, and the theory has been numerically implemented in a finite-element program. This simulation capability for SEI growth is coupled with our earlier published chemomechanical simulation capability for intercalation of Li-ions in electrode particles. Using this new combined capability we have simulated the formation and growth of an SEI layer during cyclic lithiation and delithiation of an anode particle and predicted the evolution of the growth stresses in the SEI layer. The evolution of the stress state at the SEI–particle interface for spheroidal-shaped particles is studied, and this gives us a good indicator for the propensity of potential delamination of the SEI layer from the anode particle

Diffusion–deformation theory for amorphous silicon anodes: The role of plastic deformation on electrochemical performance

Amorphous silicon (a-Si) is a promising material for anodes in Li-ion batteries due to its increased capacity relative to the current generation of graphite-based anode materials. However, the intercalation of lithium into a-Si induces very large elastic–plastic deformations, including volume changes of approximately 300%. We have formulated and numerically implemented a fully-coupled diffusion–deformation theory, which accounts for transient diffusion of lithium and accompanying large elastic–plastic deformations. The material parameters in the theory have been calibrated to experiments of galvanostatic cycling of a half-cell composed of an a-Si thin-film anode deposited on a quartz substrate, which have been reported in the literature. We show that our calibrated theory satisfactorily reproduces the mechanical response of such an anode — as measured by the changes in curvature of the substrate, as well as the electrochemical response — as measured by the voltage versus state-of-charge (SOC) response. We have applied our numerical simulation capability to model galvanostatic charging of hollow a-Si nanotubes whose exterior walls have been oxidized to prevent outward expansion; such anodes have been recently experimentally-realized in the literature. We show that the results from our numerical simulations are in good agreement with the experimentally-measured voltage versus SOC behavior at various charging rates (C-rates). Through our simulations, we have identified two major effects of plasticity on the electrochemical performance of a-Si anodes: • First, for a given voltage cut-off, plasticity enables lithiation of the anode to a higher SOC. This is because plastic flow reduces the stresses generated in the material, and thus reduces the potential required to lithiate the material. • Second, plastic deformation accounts for a significant percentage of the energy dissipated during the cycling of the anode at low C-rates. Hence, plasticity can have either (a) a beneficial effect, that is, a higher SOC for a given voltage cut-off; or (b) a detrimental effect, that is significant energy dissipation at low C-rates.National Science Foundation (U.S.) Division of Civil, Mechanical and Manufacturing Innovation (Award CMMI-1063626

Nitinol-reinforced shape-memory polymers

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 33).Reinforced shape-memory polymers have been developed from an acrylate based thermoset shape-memory polymer and nitinol wires. A rectangular shape-memory polymer measuring approximately 1 by 2 by 0.1 inches has a ten fold increase in actuation force under three-point bending when reinforced with two 0.02 inch diameter nitinol wires. A constitutive model for shape-memory polymers and nitinol has been used to predict with good correlation the actuation-versus-time and displacement-versustime behavior of the reinforced shape-memory polymer composites. It is possible then, using finite-element modeling, to design and manufacture reinforced shape-memory polymers tailored for use as thermally-activated actuators of specific force.by Claudio V. Di Leo.S.B

A coupled theory for diffusion of hydrogen and large elastic-plastic deformations of metals

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 101-103).A thermodynamically-consistent coupled-theory which accounts for diffusion of hydrogen, trapping of hydrogen, diffusion of heat, and large elastic-plastic deformations of metals is developed. Our theoretical framework places the widely-used notion of an "equilibrium" between hydrogen residing in normal interstitial lattice sites and hydrogen trapped at microstructural defects, within a thermodynamically-consistent framework. The theory has been numerically implemented in a finite element program. Using the numerical capability we study two important problems. First, we show the importance of using a prescribed chemical potential boundary condition in modeling the boundary between a metal system and a hydrogen atmosphere at a given partial pressure and temperature; specifically, we perform simulations using this boundary condition and compare our simulations to those in the published literature. Secondly, the effects of hydrogen on the plastic deformation of metals is studied through simulations of plane-strain tensile deformation and three-point bending of U-Notched specimens. Our simulations on the effects of hydrogen on three-point bending of U-notched specimens are shown to be in good qualitative agreement with published experiments.by Claudio V. Di Leo.S.M

A Finite Element Implementation of a Coupled Diffusion-Deformation Theory for Elastomeric Gels

The theory of Chester and Anand (2011) for fluid diffusion and large deformations of elastomeric gels is implemented as a user-defined element (UEL) subroutine in the commercial finite element software package ABAQUS. A specialized form of the constitutive equations and the governing partial differential equations of the theory are summarized, and the numerical implementation is described in detail. To demonstrate the robustness of the numerical implementation a few illustrative numerical simulation examples for axisymmetric, plane strain, and three-dimensional geometries are shown. For educational purposes, and also to facilitate the numerical implementation of other coupled multiphysics theories, the source code for the UEL is provided as an online supplement to this paper.National Science Foundation (U.S.) (NSF CMMI-1063626

Interplay of phase boundary anisotropy and electro-autocatalytic surface reactions on the lithium intercalation dynamics in LiX_XFePO4_4 platelet-like nanoparticles

Experiments on single crystal Li$_X$FePO$_4$ (LFP) nanoparticles indicate rich nonequilibrium phase behavior, such as suppression of phase separation at high lithiation rates, striped patterns of coherent phase boundaries, nucleation by binarysolid surface wetting and intercalation waves. These observations have been successfully predicted (prior to the experiments) by 1D depth-averaged phase-field models, which neglect any subsurface phase separation. In this paper, using an electro-chemo-mechanical phase-field model, we investigate the coherent non-equilibrium subsurface phase morphologies that develop in the $ab$- plane of platelet-like single-crystal platelet-like Li$_X$FePO$_4$ nanoparticles. Finite element simulations are performed for 2D plane-stress conditions in the $ab$- plane, and validated by 3D simulations, showing similar results. We show that the anisotropy of the interfacial tension tensor, coupled with electroautocatalytic surface intercalation reactions, plays a crucial role in determining the subsurface phase morphology. With isotropic interfacial tension, subsurface phase separation is observed, independent of the reaction kinetics, but for strong anisotropy, phase separation is controlled by surface reactions, as assumed in 1D models. Moreover, the driven intercalation reaction suppresses phase separation during lithiation, while enhancing it during delithiation, by electro-autocatalysis, in quantitative agreement with {\it in operando} imaging experiments in single-crystalline nanoparticles, given measured reaction rate constants

In Situ Lithiation–Delithiation of Mechanically Robust Cu–Si Core–Shell Nanolattices in a Scanning Electron Microscope

Nanoarchitected Cu–Si core–shell lattices were fabricated via two-photon lithography and tested as mechanically robust Li-ion battery electrodes which accommodate ∼250% Si volume expansion during lithiation. The superior mechanical performance of the nanolattice electrodes is directly observed using an in situ scanning electron microscope, which allows volume expansion and morphological changes to be imaged at multiple length scales, from single lattice beam to the architecture level, during electrochemical testing. Finite element modeling of lithiation-induced volume expansion in a core–shell structure reveals that geometry and plasticity mechanisms play a critical role in preventing damage in the nanolattice electrodes. The two-photon lithography-based fabrication method combined with computational modeling and in situ characterization capabilities would potentially enable the rational design and fast discovery of mechanically robust and kinetically agile electrode materials that independently optimize geometry, feature size, porosity, surface area, and chemical composition, as well as other functional devices in which mechanical and transport phenomena are important

organoselenium compounds an overview on the biological activities beyond antioxidant properties

For a long period, Selenium was considered mainly a toxic element and has been the object of disputes for its controversial balance between beneficial and toxic effects. Nowadays, many evidences demonstrated its role as essential microelement in mammalian diet, having an essential role in redox homeostasis of all the living systems. Around 25 proteins were discovered to contain a selenocysteine in the place of the more common sulfureted amino acid and, in this protein, selenium have the main role in the catalytic center and playng a key role in several major metabolic pathways such as thyroid hormone metabolism, antioxidant defense systems, and immune functions. Many studies report that selenium has a protective effect against some forms of cancer decreases, cardiovascular disease mortality, regulates the inflammatory mediators in asthma, maintains bone homeostasis and protects against bone loss. Antioxidant activities of organoselenium compounds has been widely studied and discussed in a number of recent review article. In this communication taking inspiration from a number of recent publications we want to highlight that other biological activities can be envisioned for organoselenium compounds deriving from the peculiar reactivity of this element

geomorphological mineralogical and geochemical evidence of pleistocene weathering conditions in the southern italian apennines

Geomorphological, mineralogical, and geochemical evidence of Pleistocene weathering conditions in the southern Italian Apennines Pleistocene weathering, uplift rates, and mass movements have been studied and correlated in a key-area of the Italian southern Apennines. The study area is the Melandro River valley, developed in a tectonically-controlled Quaternary intermontane basin of the axial zone of the chain. The goal of this paper is to assess ages and geomorphic features of two paleo-landslides and to relate them to values of uplift rates and the climate conditions in the axial zone of the chain during the Pleistocene. Uplift rates have been estimated using elevation and age of flat erosional land surfaces. In the southern area of the basin, the landscape features a wide paleo-landslide which can be ascribed to the upper part of the Lower Pleistocene on the basis of relationships with Quaternary deposits and land surfaces. Another paleo-landslide, in the northern sector of the basin, can be referred to the beginning of the Upper Pleistocene. The correlation between the ages of the two landslides and the temporal trend of the uplift rates allowed us to hypothesize that mass movements occurred in response to uplift peaks that destabilized slopes. Additionally, deciphering weathering conditions by means of the analysis of mineralogical and geochemical signals from landslide deposits and weathered horizons allowed assessment of changes in paleoclimate scenarios during the Pleistocene. The deep weathering was probably caused by the onset of warm-humid climate conditions, which may have acted as a further factor triggering landslide movements in an area already destabilized by the rapid uplift

Efectos fluidodinámicos sobre un ala debido a una configuración pusher

Se presenta un estudio experimental de los efectos producidos por una hélice en configuración pusher sobre un ala dotada de flap plain. El objetivo del trabajo es analizar las características del flujo de aire sobre el sistema y así poder determinar la efectividad del flap, fuerzas, vibraciones y demás fenómenos aerodinámicos que se generan en el sistema ala-flap. El origen del presente trabajo surge a partir de la problemática encontrada en el avión ultraliviano RANS-S12, en el cual se detectaron vibraciones y fatiga del flap en vuelo de crucero, producto del reemplazo del motor original. (Párrafo extraído del texto a modo de resumen)Facultad de Ingenierí