The newly discovered lithium-rich antiperovskite (LRAP) superionic conductors are an extremely in... more The newly discovered lithium-rich antiperovskite (LRAP) superionic conductors are an extremely interesting class of materials with potential applications as solid electrolytes in Li-ion batteries. In this work, we present a rational composition optimization strategy for maximizing the Li + conductivity in the LRAP guided by a combination of firstprinciples calculations and percolation theory. Using nudged elastic band (NEB) calculations, we show that a Cl-rich channel with Br-rich end points configuration leads to low vacancy migration barriers in the LRAP structure. By incorporating the halide-environment-dependent NEB barriers in a bond percolation model, we predict that there are potentially higher conductivity Li 3 OCl 1−x Br x structures near 0.235 ≤ x ≤ 0.395. This prediction is confirmed by AIMD simulation that finds Li 3 OCl 0.75 Br 0.25 to have a higher Li + conductivity than Li 3 OCl 0.5 Br 0.5 , the highest conductivity LRAP identified experimentally thus far. These results highlight that there is scope for further enhancing the conductivity in the LRAP chemistry. The general approach developed can potentially be extended to other ion-conducting systems, such as the structurally similar perovskite oxygen-ion conductors of interest in solid-oxide fuel cells as well as other superionic conductors. Figure 1. Unit cell of the Li 3 OCl antiperovskite. O 2− occupies the body-centered site. Li + occupy faced-centered sites forming a Li 6 O octahedron with O 2− . Cl − occupies the corner sites.
Density Functional Theory (DFT) computations can be used to build computational phase diagrams th... more Density Functional Theory (DFT) computations can be used to build computational phase diagrams that are used to understand the stability of known phases but also to assess the stability of novel, predicted compounds. The quality and predictive power of those phase diagrams ...
ABSTRACT The continued drive for high performance lithium batteries has imposed stricter requirem... more ABSTRACT The continued drive for high performance lithium batteries has imposed stricter requirements on the electrolyte materials. Solid electrolytes comprising lithium super ionic conductor materials exhibit good safety and stability and are promising to replace current organic liquid electrolytes. One major limitation in the application of Li-ion conductors is that their typical conductivity is less than 10[superscript −4] S/cm at room temperature. Recently, Kamaya et al. reported a new Li super ionic conductor Li[subscript 10]GeP[subscript 2]S[subscript 12] (LGPS), which has the highest conductivity ever achieved among solid lithium electrolytes of 12 mS/cm at room temperature (comparable conductivity with liquid electrolytes) and outstanding electrochemical performance in Li batteries.
Lithium solid electrolytes can potentially address two key limitations of the organic electrolyte... more Lithium solid electrolytes can potentially address two key limitations of the organic electrolytes used in today's lithium-ion batteries, namely, their flammability and limited electrochemical stability. However, achieving a Li(+) conductivity in the solid state comparable to existing liquid electrolytes (>1 mS cm(-1)) is particularly challenging. In this work, we reveal a fundamental relationship between anion packing and ionic transport in fast Li-conducting materials and expose the desirable structural attributes of good Li-ion conductors. We find that an underlying body-centred cubic-like anion framework, which allows direct Li hops between adjacent tetrahedral sites, is most desirable for achieving high ionic conductivity, and that indeed this anion arrangement is present in several known fast Li-conducting materials and other fast ion conductors. These findings provide important insight towards the understanding of ionic transport in Li-ion conductors and serve as desig...
ABSTRACT Significant progress has been made in Na-intercalation compounds for rechargeable Na bat... more ABSTRACT Significant progress has been made in Na-intercalation compounds for rechargeable Na batteries. P2 NaxMO2 layered oxides have been shown to have high capacity, good cyclability, and improved rate capability. In this study, we investigate the diffusion mechanisms in P-2 NaxCoO2 using ab initio molecular dynamics simulations and nudged elastic band calculations. We identify the Na diffusion mechanisms in P-2 NaxCoO2 at nondilute Na concentrations and illustrate the strong effect of Na-Na interactions on Na diffusion. Our computational results demonstrate that P-2 sodium layered oxides are fast Na ionic conductors over a wide range of Na concentrations and are promising cathode materials with high rate capabilities.
Concurrency and Computation: Practice and Experience, 2015
ABSTRACT This paper introduces FireWorks, a workflow software for running high-throughput calcula... more ABSTRACT This paper introduces FireWorks, a workflow software for running high-throughput calculation workflows at supercomputing centers. FireWorks has been used to complete over 50 million CPU-hours worth of computational chemistry and materials science calculations at the National Energy Research Supercomputing Center. It has been designed to serve the demanding high-throughput computing needs of these applications, with extensive support for (i) concurrent execution through job packing, (ii) failure detection and correction, (iii) provenance and reporting for long-running projects, (iv) automated duplicate detection, and (v) dynamic workflows (i.e., modifying the workflow graph during runtime). We have found that these features are highly relevant to enabling modern data-driven and high-throughput science applications, and we discuss our implementation strategy that rests on Python and NoSQL databases (MongoDB). Finally, we present performance data and limitations of our approach along with planned future work.
We present a high-throughput infrastructure for the automated calculation of molecular properties... more We present a high-throughput infrastructure for the automated calculation of molecular properties with a focus on battery electrolytes. The infrastructure is largely open-source and handles both practical aspects (input file generation, output file parsing, and information management) as well as more complex problems (structure matching, salt complex generation, and failure recovery). Using this infrastructure, we have computed the ionization potential (IP) and electron affinities (EA) of 4830 molecules relevant to battery electrolytes (encompassing almost 55,000 quantum mechanics calculations) at the B3LYP/ 6-31+G⁄ level. We describe automated workflows for computing redox potential, dissociation constant, and salt-molecule binding complex structure generation. We present routines for automatic recovery from calculation errors, which brings the failure rate from 9.2% to 0.8% for the QChem DFT code. Automated algorithms to check duplication between two arbitrary molecules and structures are described. We present benchmark data on basis sets and functionals on the G2-97 test set; one finding is that a IP/EA calculation method that combines PBE geometry optimization and B3LYP energy evaluation requires less computational cost and yields nearly identical results as compared to a full B3LYP calculation, and could be suitable for the calculation of large molecules. Our data indicates that among the 8 functionals tested, XYGJ-OS and B3LYP are the two best functionals to predict IP/EA with an RMSE of 0.12 and 0.27 eV, respectively. Application of our automated workflow to a large set of quinoxaline derivative molecules shows that functional group effect and substitution position effect can be separated for IP/EA of quinoxaline derivatives, and the most sensitive position is different for IP and EA.
ABSTRACT In this paper, we describe the Materials Application Programming Interface (API), a simp... more ABSTRACT In this paper, we describe the Materials Application Programming Interface (API), a simple, flexible and efficient interface to programmatically query and interact with the Materials Project database based on the REpresentational State Transfer (REST) pattern for the web. Since its creation in Aug 2012, the Materials API has been the Materials Project’s de facto platform for data access, supporting not only the Materials Project’s many collaborative efforts but also enabling new applications and analyses. We will highlight some of these analyses enabled by the Materials API, particularly those requiring consolidation of data on a large number of materials, such as data mining of structural and property trends, and generation of phase diagrams. We will conclude with a discussion of the role of the API in building a community that is developing novel applications and analyses based on Materials Project data.
Computational screening techniques have been found to be an effective alternative to the trial an... more Computational screening techniques have been found to be an effective alternative to the trial and error of experimentation for discovery of new materials. With increased interest in development of advanced electrical energy storage systems, it is essential to find new electrolytes that function effectively. This Perspective reviews various methods for screening electrolytes and then describes a hierarchical computational scheme to screen multiple properties of advanced electrical energy storage electrolytes using high-throughput quantum chemical calculations. The approach effectively down-selects a large pool of candidates based on successive property evaluation. As an example, results of screening are presented for redox potentials, solvation energies, and structural changes of ∼1400 organic molecules for nonaqueous redox flow batteries. Importantly, on the basis of high-throughput screening, in silico design of suitable candidate molecules for synthesis and electrochemical testing can be achieved. We anticipate that the computational approach described in this Perspective coupled with experimentation will have a significant role to play in the discovery of materials for future energy needs.
High voltage and high thermal safety are desirable characteristics of cathode materials, but diff... more High voltage and high thermal safety are desirable characteristics of cathode materials, but difficult to achieve simultaneously. This work uses high-throughput density functional theory computations to evaluate the link between voltage and safety (as estimated by thermodynamic O 2 release temperatures) for over 1400 cathode materials. Our study indicates that a strong inverse relationship exists between voltage and safety: just over half the variance in O 2 release temperature can be explained by voltage alone. We examine the effect of polyanion group, redox couple, and ratio of oxygen to counter-cation on both voltage and safety. As expected, our data demonstrates that polyanion groups improve safety when comparing compounds with similar voltages. However, a counterintuitive result of our study is that polyanion groups produce either no benefit or reduce safety when comparing compounds with the same redox couple. Using our data set, we tabulate voltages and oxidation potentials for over 105 combinations of redox couple/anion, which can be used towards the design and rationalization of new cathode materials. Overall, only a few compounds in our study, representing limited redox couple/polyanion combinations, exhibit both high voltage and high safety. We discuss these compounds in more detail as well as the opportunities for designing safe, high-voltage cathodes.
The newly discovered lithium-rich antiperovskite (LRAP) superionic conductors are an extremely in... more The newly discovered lithium-rich antiperovskite (LRAP) superionic conductors are an extremely interesting class of materials with potential applications as solid electrolytes in Li-ion batteries. In this work, we present a rational composition optimization strategy for maximizing the Li + conductivity in the LRAP guided by a combination of firstprinciples calculations and percolation theory. Using nudged elastic band (NEB) calculations, we show that a Cl-rich channel with Br-rich end points configuration leads to low vacancy migration barriers in the LRAP structure. By incorporating the halide-environment-dependent NEB barriers in a bond percolation model, we predict that there are potentially higher conductivity Li 3 OCl 1−x Br x structures near 0.235 ≤ x ≤ 0.395. This prediction is confirmed by AIMD simulation that finds Li 3 OCl 0.75 Br 0.25 to have a higher Li + conductivity than Li 3 OCl 0.5 Br 0.5 , the highest conductivity LRAP identified experimentally thus far. These results highlight that there is scope for further enhancing the conductivity in the LRAP chemistry. The general approach developed can potentially be extended to other ion-conducting systems, such as the structurally similar perovskite oxygen-ion conductors of interest in solid-oxide fuel cells as well as other superionic conductors. Figure 1. Unit cell of the Li 3 OCl antiperovskite. O 2− occupies the body-centered site. Li + occupy faced-centered sites forming a Li 6 O octahedron with O 2− . Cl − occupies the corner sites.
Density Functional Theory (DFT) computations can be used to build computational phase diagrams th... more Density Functional Theory (DFT) computations can be used to build computational phase diagrams that are used to understand the stability of known phases but also to assess the stability of novel, predicted compounds. The quality and predictive power of those phase diagrams ...
ABSTRACT The continued drive for high performance lithium batteries has imposed stricter requirem... more ABSTRACT The continued drive for high performance lithium batteries has imposed stricter requirements on the electrolyte materials. Solid electrolytes comprising lithium super ionic conductor materials exhibit good safety and stability and are promising to replace current organic liquid electrolytes. One major limitation in the application of Li-ion conductors is that their typical conductivity is less than 10[superscript −4] S/cm at room temperature. Recently, Kamaya et al. reported a new Li super ionic conductor Li[subscript 10]GeP[subscript 2]S[subscript 12] (LGPS), which has the highest conductivity ever achieved among solid lithium electrolytes of 12 mS/cm at room temperature (comparable conductivity with liquid electrolytes) and outstanding electrochemical performance in Li batteries.
Lithium solid electrolytes can potentially address two key limitations of the organic electrolyte... more Lithium solid electrolytes can potentially address two key limitations of the organic electrolytes used in today's lithium-ion batteries, namely, their flammability and limited electrochemical stability. However, achieving a Li(+) conductivity in the solid state comparable to existing liquid electrolytes (>1 mS cm(-1)) is particularly challenging. In this work, we reveal a fundamental relationship between anion packing and ionic transport in fast Li-conducting materials and expose the desirable structural attributes of good Li-ion conductors. We find that an underlying body-centred cubic-like anion framework, which allows direct Li hops between adjacent tetrahedral sites, is most desirable for achieving high ionic conductivity, and that indeed this anion arrangement is present in several known fast Li-conducting materials and other fast ion conductors. These findings provide important insight towards the understanding of ionic transport in Li-ion conductors and serve as desig...
ABSTRACT Significant progress has been made in Na-intercalation compounds for rechargeable Na bat... more ABSTRACT Significant progress has been made in Na-intercalation compounds for rechargeable Na batteries. P2 NaxMO2 layered oxides have been shown to have high capacity, good cyclability, and improved rate capability. In this study, we investigate the diffusion mechanisms in P-2 NaxCoO2 using ab initio molecular dynamics simulations and nudged elastic band calculations. We identify the Na diffusion mechanisms in P-2 NaxCoO2 at nondilute Na concentrations and illustrate the strong effect of Na-Na interactions on Na diffusion. Our computational results demonstrate that P-2 sodium layered oxides are fast Na ionic conductors over a wide range of Na concentrations and are promising cathode materials with high rate capabilities.
Concurrency and Computation: Practice and Experience, 2015
ABSTRACT This paper introduces FireWorks, a workflow software for running high-throughput calcula... more ABSTRACT This paper introduces FireWorks, a workflow software for running high-throughput calculation workflows at supercomputing centers. FireWorks has been used to complete over 50 million CPU-hours worth of computational chemistry and materials science calculations at the National Energy Research Supercomputing Center. It has been designed to serve the demanding high-throughput computing needs of these applications, with extensive support for (i) concurrent execution through job packing, (ii) failure detection and correction, (iii) provenance and reporting for long-running projects, (iv) automated duplicate detection, and (v) dynamic workflows (i.e., modifying the workflow graph during runtime). We have found that these features are highly relevant to enabling modern data-driven and high-throughput science applications, and we discuss our implementation strategy that rests on Python and NoSQL databases (MongoDB). Finally, we present performance data and limitations of our approach along with planned future work.
We present a high-throughput infrastructure for the automated calculation of molecular properties... more We present a high-throughput infrastructure for the automated calculation of molecular properties with a focus on battery electrolytes. The infrastructure is largely open-source and handles both practical aspects (input file generation, output file parsing, and information management) as well as more complex problems (structure matching, salt complex generation, and failure recovery). Using this infrastructure, we have computed the ionization potential (IP) and electron affinities (EA) of 4830 molecules relevant to battery electrolytes (encompassing almost 55,000 quantum mechanics calculations) at the B3LYP/ 6-31+G⁄ level. We describe automated workflows for computing redox potential, dissociation constant, and salt-molecule binding complex structure generation. We present routines for automatic recovery from calculation errors, which brings the failure rate from 9.2% to 0.8% for the QChem DFT code. Automated algorithms to check duplication between two arbitrary molecules and structures are described. We present benchmark data on basis sets and functionals on the G2-97 test set; one finding is that a IP/EA calculation method that combines PBE geometry optimization and B3LYP energy evaluation requires less computational cost and yields nearly identical results as compared to a full B3LYP calculation, and could be suitable for the calculation of large molecules. Our data indicates that among the 8 functionals tested, XYGJ-OS and B3LYP are the two best functionals to predict IP/EA with an RMSE of 0.12 and 0.27 eV, respectively. Application of our automated workflow to a large set of quinoxaline derivative molecules shows that functional group effect and substitution position effect can be separated for IP/EA of quinoxaline derivatives, and the most sensitive position is different for IP and EA.
ABSTRACT In this paper, we describe the Materials Application Programming Interface (API), a simp... more ABSTRACT In this paper, we describe the Materials Application Programming Interface (API), a simple, flexible and efficient interface to programmatically query and interact with the Materials Project database based on the REpresentational State Transfer (REST) pattern for the web. Since its creation in Aug 2012, the Materials API has been the Materials Project’s de facto platform for data access, supporting not only the Materials Project’s many collaborative efforts but also enabling new applications and analyses. We will highlight some of these analyses enabled by the Materials API, particularly those requiring consolidation of data on a large number of materials, such as data mining of structural and property trends, and generation of phase diagrams. We will conclude with a discussion of the role of the API in building a community that is developing novel applications and analyses based on Materials Project data.
Computational screening techniques have been found to be an effective alternative to the trial an... more Computational screening techniques have been found to be an effective alternative to the trial and error of experimentation for discovery of new materials. With increased interest in development of advanced electrical energy storage systems, it is essential to find new electrolytes that function effectively. This Perspective reviews various methods for screening electrolytes and then describes a hierarchical computational scheme to screen multiple properties of advanced electrical energy storage electrolytes using high-throughput quantum chemical calculations. The approach effectively down-selects a large pool of candidates based on successive property evaluation. As an example, results of screening are presented for redox potentials, solvation energies, and structural changes of ∼1400 organic molecules for nonaqueous redox flow batteries. Importantly, on the basis of high-throughput screening, in silico design of suitable candidate molecules for synthesis and electrochemical testing can be achieved. We anticipate that the computational approach described in this Perspective coupled with experimentation will have a significant role to play in the discovery of materials for future energy needs.
High voltage and high thermal safety are desirable characteristics of cathode materials, but diff... more High voltage and high thermal safety are desirable characteristics of cathode materials, but difficult to achieve simultaneously. This work uses high-throughput density functional theory computations to evaluate the link between voltage and safety (as estimated by thermodynamic O 2 release temperatures) for over 1400 cathode materials. Our study indicates that a strong inverse relationship exists between voltage and safety: just over half the variance in O 2 release temperature can be explained by voltage alone. We examine the effect of polyanion group, redox couple, and ratio of oxygen to counter-cation on both voltage and safety. As expected, our data demonstrates that polyanion groups improve safety when comparing compounds with similar voltages. However, a counterintuitive result of our study is that polyanion groups produce either no benefit or reduce safety when comparing compounds with the same redox couple. Using our data set, we tabulate voltages and oxidation potentials for over 105 combinations of redox couple/anion, which can be used towards the design and rationalization of new cathode materials. Overall, only a few compounds in our study, representing limited redox couple/polyanion combinations, exhibit both high voltage and high safety. We discuss these compounds in more detail as well as the opportunities for designing safe, high-voltage cathodes.
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Papers by Shyue Ping Ong