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      Lithiation of Silicon Anode based on Soft X-ray Emission Spectroscopy: A Theoretical Study

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          Abstract

          Due to its exceptional lithium storage capacity silicon is considered as a promising candidate for anode material in lithium-ion batteries (LIBs). In the present work we demonstrate that methods of the soft X-ray emission spectroscopy (SXES) can be used as a powerful tool for the comprehensive analysis of the electronic and structural properties of lithium silicides Li\(_{x}\)Si forming in LIB's anode upon Si lithiation. On the basis of density functional theory (DFT) and molecular dynamics (MD) simulations it is shown that coordination of Si atoms in Li\(_{x}\)Si decreases with increase in Li concentration both for the crystalline and amorphous phases. In amorphous a-Li\(_{x}\)Si alloys Si tends to cluster forming Si-Si covalent bonds even at the high lithium concentration. It is demonstrated that the Si-L\(_{2,3}\) emission bands of the crystalline and amorphous Li\(_{x}\)Si alloys show different spectral dependencies reflecting the process of disintegration of Si-Si network into Si clusters and chains of the different sizes upon Si lithiation. The Si-L\(_{2,3}\) emission band of Li\(_{x}\)Si alloys become narrower and shifts towards higher energies with an increase in Li concentration. The shape of the emission band depends on the relative contribution of the X-ray radiation from the Si atoms having different coordination. This feature of the Si-L\(_{2,3}\) spectra of Li\(_{x}\)Si alloys can be used for the detailed analysis of the Si lithiation process and LIB's anode structure identification.

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          Most cited references 26

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          Soft self-consistent pseudopotentials in a generalized eigenvalue formalism

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            Relativistic separable dual-space Gaussian Pseudopotentials from H to Rn

            We generalize the concept of separable dual-space Gaussian pseudopotentials to the relativistic case. This allows us to construct this type of pseudopotential for the whole periodic table and we present a complete table of pseudopotential parameters for all the elements from H to Rn. The relativistic version of this pseudopotential retains all the advantages of its nonrelativistic version. It is separable by construction, it is optimal for integration on a real space grid, it is highly accurate and due to its analytic form it can be specified by a very small number of parameters. The accuracy of the pseudopotential is illustrated by an extensive series of molecular calculations.
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              In situ observation of the electrochemical lithiation of a single SnO₂ nanowire electrode.

              We report the creation of a nanoscale electrochemical device inside a transmission electron microscope--consisting of a single tin dioxide (SnO(2)) nanowire anode, an ionic liquid electrolyte, and a bulk lithium cobalt dioxide (LiCoO(2)) cathode--and the in situ observation of the lithiation of the SnO(2) nanowire during electrochemical charging. Upon charging, a reaction front propagated progressively along the nanowire, causing the nanowire to swell, elongate, and spiral. The reaction front is a "Medusa zone" containing a high density of mobile dislocations, which are continuously nucleated and absorbed at the moving front. This dislocation cloud indicates large in-plane misfit stresses and is a structural precursor to electrochemically driven solid-state amorphization. Because lithiation-induced volume expansion, plasticity, and pulverization of electrode materials are the major mechanical effects that plague the performance and lifetime of high-capacity anodes in lithium-ion batteries, our observations provide important mechanistic insight for the design of advanced batteries.
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                Author and article information

                Journal
                06 January 2018
                Article
                1801.01983

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

                Custom metadata
                physics.chem-ph cond-mat.mtrl-sci

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