This article examines three key questions in environmental analysis of EVs and their batteries that influence EV-to-ICV comparative environmental performance.

This paper aims to help fill a gap in the literature on Li-ion battery electrode materials due to the absence of measured elastic constants needed for diffusion induced stress models. By examining results from new first principles density functional theory (DFT) calculations of LiCoO 2 , LiMn 2 O 4 , (and their delithiated hosts, CoO 2 and MnO 2 ), Li x Al alloys, and data from the extant literature on LiFePO 4 (and FePO 4 ), LiTi 2 O 4 (and Li 2 Ti 2 O 4 ), Li x Si, Li x Sn and lihtium graphite-interaction-compounds, a compelling picture emerges on the dependency of the elastic properties on Li concentration. Specifically, three distinct categories of behavior are found: (a) the averaged Young's moduli change very minimally upon lithiation of the spinel and olivine structures; (b) lithiation induced stiffening is observed only when new and stronger bonds between the Li ions and the host materials are formed in layered compounds; and (c) for alloy-forming electrode materials, such as Si, β-Sn and Al, the averaged Young's moduli of lithiated compounds follow the linear rule of mixtures. The tendency of ductile or brittle behavior electrode materials is investigated with the Pugh criterion, and a ductile to brittle transition was found to occur during lithiation of Al and β-Sn, but not in Si. One of the critical challenges in advanced lithium-ion (Li-ion) batteries is preventing fracture and mechanical failure of electrodes during lithium insertion and de-insertion. Most Li-ion battery electrodes experience volume changes associated with Li concentration changes within the host particles during charging and discharging.1 Graphite, for example, is the most common negative electrode for Li-ion batteries. Its volume increases by as much as 10% when Li intercalates between the sheets of C atoms.2 Compared to graphite, Si can store ∼10 times more Li, but it undergoes a massive volume expansion of the order of 300%.3 The large volume expansion, phase transition, and the associated Li diffusion-induced stresses (DIS) within electrode materials can lead to their fracture and failure which results in battery capacity loss and power fade.Significant progress toward understanding how DIS can be minimized to increase mechanical durability of Li-ion batteries 4-13 has been made. For example, Verbrugge and Cheng 11 modeled the evolution of stress and strain energy within a spherically-shaped electrode particle under either galvanostatic or potentiostatic operation. They also investigated the effects of surface energy and surface elasticity on the stress evolution in spherical electrodes.10 Wolfenstine 14 demonstrated that using Young's modulus, fracture toughness, and volume change, a critical particle size needed to lower capacity fade could be estimated with an analytical model. Recent models have been more material specific. Woodford et al. 15 further derived a failure criterion for crack propagation in individual Li x Mn 2 O 4 electrode particles during galvanostatic charging based on fracture mechanics. Using a combination...

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The tendency for C(60) nanowires to persist on two monolayers of recumbent pentacene is studied using molecular dynamics (MD) simulations. A review of existing experimental literature for the tilt angle adopted by pentacene on noble metal surfaces shows that studies cover a limited range from 55° to 90°, motivating simulation studies of essentially the entire range of tilt angles (10°-90°) to predict the optimum surface tilt angle for C(60) nanowire formation. The persistence of a 1D nanowire depends sensitively on this tilt angle, the amount of initial tensile strain, and the presence of surface step edges. At room temperature, C(60) nanowires oriented along the pentacene short axes persist for several nanoseconds and are more likely to occur if they reside between, or within, pentacene rows for ϕ ≤ ∼60°. The likelihood of this persistence increases the smaller the tilt angle. Nanowires oriented along the long axes of pentacene molecules are unlikely to form. The limit of stability of nanowires was tested by raising the temperature to 400 K. Nanowires located between pentacene rows survived this temperature rise, but those located initially within pentacene rows are only stable in the range ϕ(1) = 30°-50°. Flatter pentacene surfaces, that is, tilt angles above about 60°, are subject to disorder caused by C(60) molecules "burrowing" into the pentacene surface. An initial strain of 5% applied to the C(60) nanowires significantly decreases the likelihood of nanowire persistence. In contrast, any appreciable surface roughness, even by half a monolayer in height of a third pentacene monolayer, strongly enhances the likelihood of nanowire formation due to the strong binding energy of C(60) molecules to step edges.

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High-capacity battery cathode materials containing Li 2 MnO 3 appear to be activated during the first electrochemical cycle through the generation of oxygen vacancies. These oxygen vacancies have been predicted to alter the atomistic scale structure of Li 2 MnO 3 and thus impact the delithiation process. In order to understand the effects of these oxygen vacancies we computationally determine the location of lithium removal in Li 2 MnO 3-δ (δ=0, 0.0625 and 0.125) and study lithium diffusion in Li 2-x MnO 3-δ. This study shows that it is energetically favorable for the lithium vacancies to form in the neighboring positions of the oxygen vacancies, suggesting that there is a strong interaction between the two vacancy types. This interaction also inhibits the diffusion of the lithium-ions, as seen in ab-initio molecular dynamics simulations where less hopping of lithium atoms is observed when oxygen vacancies are present. Additionally, the oxygen vacancy containing structures lead to an increase in the energy barrier for lithium hopping and the calculated diffusion coefficient decreases by ~5 orders of magnitude from the perfect crystal structure.

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