Combined first-principles statistical mechanics approach to sulfur structure in organic cathode hosts for polymer based lithium-sulfur (Li-S) batteries.
TL;DR: In this article, a combination of electronic structure theory and statistical mechanics is presented to characterize the structure of the initial state of the charged cathode on an atomic level, and a stability analysis of differently sulfurized TBT dimers as the basic polymer unit calculated within density functional theory is performed.
Abstract: Polymer-based batteries that utilize organic electrode materials are considered viable candidates to overcome the common drawbacks of lithium-sulfur (Li-S) batteries. A promising cathode can be developed using a conductive, flexible, and free-standing polymer, poly(4-thiophen-3-yl)benzenethiol) (PTBT), as the sulfur host material. By a vulcanization process, sulfur is embedded into this polymer. Here, we present a combination of electronic structure theory and statistical mechanics to characterize the structure of the initial state of the charged cathode on an atomic level. We perform a stability analysis of differently sulfurized TBT dimers as the basic polymer unit calculated within density-functional theory (DFT) and combine this with a statistical binding model for the binding probability distributions of the vulcanization process. From this, we deduce sulfur chain length ("rank") distributions and calculate the average sulfur rank depending on the sulfur concentration and temperature. This multi-scale approach allows us to bridge the gap between the local description of the covalent bonding process and the derivation of the macroscopic properties of the cathode. Our calculations show that the main reaction of the vulcanization process leads to high-probability states of sulfur chains cross-linking TBT units belonging to different polymer backbones, with a dominant rank around n = 5. In contrast, the connection of adjacent TBT units of the same polymer backbone by a sulfur chain is the side reaction. These results are experimentally supported by Raman spectroscopy.
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TL;DR: In this paper , the concept of constructing binder and carbon additive-free organosulfur cathode was proved based on thiol-containing conducting polymer poly(4−(thiophene•3yl) benzenethiol) (PTBT).
Abstract: Abstract Herein, the concept of constructing binder‐ and carbon additive‐free organosulfur cathode was proved based on thiol‐containing conducting polymer poly(4‐(thiophene‐3‐yl) benzenethiol) (PTBT). The PTBT featured the polythiophene‐structure main chain as a highly conducting framework and the benzenethiol side chain to copolymerize with sulfur and form a crosslinked organosulfur polymer (namely S/PTBT). Meanwhile, it could be in‐situ deposited on the current collector by electro‐polymerization, making it a binder‐free and free‐standing cathode for Li‐S batteries. The S/PTBT cathode exhibited a reversible capacity of around 870 mAh g−1 at 0.1 C and improved cycling performance compared to the physically mixed cathode (namely S&PTBT). This multifunction cathode eliminated the influence of the additives (carbon/binder), making it suitable to be applied as a model electrode for operando analysis. Operando X‐ray imaging revealed the remarkable effect in the suppression of polysulfides shuttle via introducing covalent bonds, paving the way for the study of the intrinsic mechanisms in Li‐S batteries.
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TL;DR: In this article , the potential of combining strong nitrogen-sulfur interactions, which has been recently shown to lead to a shuttle-free discharge mechanism, and superior electrical conductivity of graphene nanoribbons is explored in S/N-GNR copolymers.
Abstract: Conductive sulfur/carbon copolymers with a high reversible capacity are promising alternative cathode materials for lithium-sulfur batteries. Here, the focus is set on nitrogen-terminated zigzag graphene nanoribbons (N-GNRs) resembling intermediate product of electrospun polyacrylonitrile (PAN)-based carbon nanofibers. In particular, the possibility of combining strong nitrogen-sulfur interactions, which has been recently shown to lead to a shuttle-free discharge mechanism, and superior electrical conductivity of graphene nanoribbons is explored in S/N-GNR copolymers. Structural and electronic properties of ${\mathrm{S}}_{x}/$N-GNR structures, $x=1,\dots{},8$, prior and during the discharge are studied using density-functional theory calculations along with ab initio molecular dynamics simulations. It is found that the GNR backbone assumes a rippled structures in all S/N-GNR structures considered here. The most favorable sulfur structures in S/N-GNR copolymers are found to consist of short sulfur chains with $x\ensuremath{\sim}4,5$. It is also observed that, similar to N-GNRs, S/N-GNR copolymers show a metallic behavior which is brought about by the conductive backbone. In addition, consecutive lithiation reactions are studied and product structures are obtained. It is demonstrated that a shuttle-free, solid-solid transformation could also be expected during the discharge of S/N-GNR copolymers, whereas the lithiated structures remain electrically conductive, irrespective of the discharge state. Therefore, the current study promotes the use of S/N-GNR copolymers as an alternative to other poorly conductive PAN-based S/C copolymer cathodes for lithium-sulfur batteries (such as S/cPAN), while largely mitigating lithium polysulfide formation.
1 citations
TL;DR: In this paper , the influence of the regiochemistry of a conjugated poly(4-(thiophene-3-yl)benzenethiol) (PTBT) polymer on its aggregation behavior and charge transport was explored.
Abstract: For lithium–sulfur (Li–S) batteries to become competitive, they require high stability and energy density. Organosulfur polymer-based cathodes have recently shown promising performance due to their ability to overcome common limitations of Li–S batteries, such as the insulating nature of sulfur. In this study, we use a multiscale modeling approach to explore the influence of the regiochemistry of a conjugated poly(4-(thiophene-3-yl)benzenethiol) (PTBT) polymer on its aggregation behavior and charge transport. Classical molecular dynamics simulations of the self-assembly of polymer chains with different regioregularity show that a head-to-tail/head-to-tail regularity can form a well-ordered crystalline phase of planar chains allowing for fast charge transport. Our X-ray diffraction measurements, in conjunction with our predicted crystal structure, confirm the presence of crystalline phases in the electropolymerized PTBT polymer. We quantitatively describe the charge transport in the crystalline phase in a band-like regime. Our results give detailed insights into the interplay between microstructural and electrical properties of conjugated polymer cathode materials, highlighting the effect of polymer chain regioregularity on its charge transport properties.
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TL;DR: Inverse vulcanization method to obtain sulfur-based polymers as alternative to sulfur resemble the redox activity of sulfur as discussed by the authors , therefore, inversely vulcanized polymers are evolving materials in Li-S batteries.
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TL;DR: A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif
146,533 citations
TL;DR: In this paper, an analysis of the performances of a parameter free density functional model (PBE0) obtained combining the so-called PBE generalized gradient functional with a predefined amount of exact exchange is presented.
Abstract: We present an analysis of the performances of a parameter free density functional model (PBE0) obtained combining the so called PBE generalized gradient functional with a predefined amount of exact exchange. The results obtained for structural, thermodynamic, kinetic and spectroscopic (magnetic, infrared and electronic) properties are satisfactory and not far from those delivered by the most reliable functionals including heavy parameterization. The way in which the functional is derived and the lack of empirical parameters fitted to specific properties make the PBE0 model a widely applicable method for both quantum chemistry and condensed matter physics.
13,411 citations
TL;DR: In this paper, the authors reviewed the challenges for further development of Li rechargeable batteries for electric vehicles and proposed a nonflammable electrolyte with either a larger window between its lowest unoccupied molecular orbital and highest occupied molecular orbital (HOMO) or a constituent that can develop rapidly a solid/ electrolyte-interface (SEI) layer to prevent plating of Li on a carbon anode during a fast charge of the battery.
Abstract: The challenges for further development of Li rechargeable batteries for electric vehicles are reviewed. Most important is safety, which requires development of a nonflammable electrolyte with either a larger window between its lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) or a constituent (or additive) that can develop rapidly a solid/ electrolyte-interface (SEI) layer to prevent plating of Li on a carbon anode during a fast charge of the battery. A high Li-ion conductivity (σ Li > 10 ―4 S/cm) in the electrolyte and across the electrode/ electrolyte interface is needed for a power battery. Important also is an increase in the density of the stored energy, which is the product of the voltage and capacity of reversible Li insertion/extraction into/from the electrodes. It will be difficult to design a better anode than carbon, but carbon requires formation of an SEI layer, which involves an irreversible capacity loss. The design of a cathode composed of environmentally benign, low-cost materials that has its electrochemical potential μ C well-matched to the HOMO of the electrolyte and allows access to two Li atoms per transition-metal cation would increase the energy density, but it is a daunting challenge. Two redox couples can be accessed where the cation redox couples are "pinned" at the top of the O 2p bands, but to take advantage of this possibility, it must be realized in a framework structure that can accept more than one Li atom per transition-metal cation. Moreover, such a situation represents an intrinsic voltage limit of the cathode, and matching this limit to the HOMO of the electrolyte requires the ability to tune the intrinsic voltage limit. Finally, the chemical compatibility in the battery must allow a long service life.
8,535 citations
TL;DR: The work presented here details the Avogadro library, which is a framework providing a code library and application programming interface (API) with three-dimensional visualization capabilities; and has direct applications to research and education in the fields of chemistry, physics, materials science, and biology.
Abstract: The Avogadro project has developed an advanced molecule editor and visualizer designed for cross-platform use in computational chemistry, molecular modeling, bioinformatics, materials science, and related areas. It offers flexible, high quality rendering, and a powerful plugin architecture. Typical uses include building molecular structures, formatting input files, and analyzing output of a wide variety of computational chemistry packages. By using the CML file format as its native document type, Avogadro seeks to enhance the semantic accessibility of chemical data types. The work presented here details the Avogadro library, which is a framework providing a code library and application programming interface (API) with three-dimensional visualization capabilities; and has direct applications to research and education in the fields of chemistry, physics, materials science, and biology. The Avogadro application provides a rich graphical interface using dynamically loaded plugins through the library itself. The application and library can each be extended by implementing a plugin module in C++ or Python to explore different visualization techniques, build/manipulate molecular structures, and interact with other programs. We describe some example extensions, one which uses a genetic algorithm to find stable crystal structures, and one which interfaces with the PackMol program to create packed, solvated structures for molecular dynamics simulations. The 1.0 release series of Avogadro is the main focus of the results discussed here. Avogadro offers a semantic chemical builder and platform for visualization and analysis. For users, it offers an easy-to-use builder, integrated support for downloading from common databases such as PubChem and the Protein Data Bank, extracting chemical data from a wide variety of formats, including computational chemistry output, and native, semantic support for the CML file format. For developers, it can be easily extended via a powerful plugin mechanism to support new features in organic chemistry, inorganic complexes, drug design, materials, biomolecules, and simulations. Avogadro is freely available under an open-source license from http://avogadro.openmolecules.net
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5,816 citations
TL;DR: It is shown that the effective atomic C6 coefficients depend strongly on the bonding environment of an atom in a molecule, and the van der Waals radii and the damping function in the C6R(-6) correction method for density-functional theory calculations.
Abstract: We present a parameter-free method for an accurate determination of long-range van der Waals interactions from mean-field electronic structure calculations. Our method relies on the summation of interatomic C6 coefficients, derived from the electron density of a molecule or solid and accurate reference data for the free atoms. The mean absolute error in the C6 coefficients is 5.5% when compared to accurate experimental values for 1225 intermolecular pairs, irrespective of the employed exchangecorrelation functional. We show that the effective atomic C6 coefficients depend strongly on the bonding environment of an atom in a molecule. Finally, we analyze the van der Waals radii and the damping function in the C6R � 6 correction method for density-functional theory calculations.
4,825 citations