Ab Initio Molecular Dynamics Calculations Research Articles

Configurational and Dynamical Heterogeneity in Superionic Li5.3PS4.3Cl1.7−xBrx

AbstractThe correlation between lattice chemistry and cation migration in high‐entropy Li+ conductors is not fully understood due to challenges in characterizing anion disorder. To address this issue, argyrodite family of Li+ conductors, which enables structural engineering of the anion lattice, is investigated. Specifically, new argyrodites, Li5.3PS4.3Cl1.7−xBrx (0 ≤ x ≤ 1.7), with varying anion entropy are synthesized and X‐ray diffraction, neutron scattering, and multinuclear high‐resolution solid‐state nuclear magnetic resonance (NMR) are used to determine the resulting structures. Ion and lattice dynamics are determined using variable‐temperature multinuclear NMR relaxometry and maximum entropy method analysis of neutron scattering, aided by constrained ab initio molecular dynamics calculations. 15 atomic configurations of anion arrangements are identified, producing a wide range of local lattice dynamics. High entropy in the lattice structure, composition, and dynamics stabilize otherwise metastable Li‐deficient structures and flatten the energy landscape for cation migration. This resulted in the highest room‐temperature ionic conductivity of 26 mS cm−1 and a low activation energy of 0.155 eV realized in Li5.3PS4.3Cl0.7Br, where anion disorder is maximized. This study sheds light on the complex structure–property relationships of high‐entropy superionic conductors, highlighting the significance of heterogeneity in lattice dynamics.

A computational study of 2D group-III ternary chalcogenide monolayer compounds MNTe2 (M, N = In, Ga, Al)

First principle calculations of novel two-dimensional (2D) group-III ternary chalcogenide monolayer (G3TCM) compounds have been carried out using density functional theory. The 2D hexagonal structure has a honeycomb-like appearance from both the top and bottom views. Both pristine and G3TCM compounds are energetically favourable and have been found to be dynamically stable via phonon calculations. The ab-initio molecular dynamics calculations show the thermodynamical stability of the G3TCM compounds. The G3TCM compounds exhibit semiconductor behaviour with a decreased indirect bandgap compared to the pristine monolayers. Chalcogen atoms contribute mainly to the valence bands, while group-III atoms have a major contribution to the conduction band. A red shift has been observed in the absorption of light, mainly in the visible and ultraviolet regions, and the refractive index is increased compared to the pristine material. Both pristine and G3TCM compounds have been found to be more active in the ultraviolet region, and low reflection has been observed. In the 6–8 eV range of the ultraviolet region, zero reflection and the highest absorption are observed. The monolayer has shown potential applications in optoelectronics devices as an ultraviolet and visible light detector, absorber, coating material, and more. The band alignment of the 2D G3TCM monolayer is calculated to observe its photo-catalyst behaviour.

Rydberg-type electronic excited state dynamics in small sodium–water clusters

Equilibrium geometries and thermodynamic potentials of the neutral and ionised species of the Na ⋯ ( H 2 O ) n ( n = 1 , . . , 8 ) mixed clusters were computed at MN15/def2-TZVPD level of density functional theory (DFT). The vertical and adiabatic ionisation energies and enthalpies were computed and their cluster size dependence was discussed. Laser-induced ionisation involves electronic excitation through Rydberg-type excited states, which have been characterised using the TDDFT method, including the ωB2PLYP double-hybrid exchange-correlation functional. Ab initio molecular dynamics calculations were performed on a time scale of 20 picoseconds. Fluctuations of the charge and the sodium–oxygen atomic distances predict that, the 3 s 1 electron of the sodium atom are transferred from the delocalised Rydberg orbitals to the Rydberg orbitals around the water molecules and the sodium atom becomes positively charged with around 0.6e after the first 10 ps . On the other hand, some of the water molecules can move away up to 5 Å from the sodium with a significant negative charge on them. It has been shown that non-radiative relaxation cannot be excluded, they can mostly occur for cases n ⩾ 4 . The results confirm that the adiabatic photo-ionisation can occur on the basis of cluster disintegration.

Speciation and Reactivity Control of Cu-Oxo Clusters via Extraframework Al in Mordenite for Methane Oxidation.

The stoichiometric conversion of methane to methanol by Cu-exchanged zeolites can be brought to highest yields by the presence of extraframework Al and high CH4 chemical potentials. Combining theory and experiments, the differences in chemical reactivity of monometallic Cu-oxo and bimetallic Cu-Al-oxo nanoclusters stabilized in zeolite mordenite (MOR) are investigated. Cu-L3 edge X-ray absorption near-edge structure (XANES), infrared (IR), and ultraviolet-visible (UV-vis) spectroscopies, in combination with CH4 oxidation activity tests, support the presence of two types of active clusters in MOR and allow quantification of the relative proportions of each type in dependence of the Cu concentration. Ab initio molecular dynamics (MD) calculations and thermodynamic analyses indicate that the superior performance of materials enriched in Cu-Al-oxo clusters is related to the activity of two μ-oxo bridges in the cluster. Replacing H2O with ethanol in the product extraction step led to the formation of ethyl methyl ether, expanding this way the applicability of these materials for the activation and functionalization of CH4. We show that competition between different ion-exchanged metal-oxo structures during the synthesis of Cu-exchanged zeolites determines the formation of active species, and this provides guidelines for the synthesis of highly active materials for CH4 activation and functionalization.

Ab initio molecular dynamics study of H2 dissociation mechanisms on Cu13 and defective graphene-supported Cu13 clusters: active sites, energy barriers and adsorption states.

Ab initio molecular dynamics calculations were performed to study H2 dissociation mechanisms on Cu13 and defective graphene-supported Cu13 clusters. The study reveals that seven types of corresponding dissociation processes are found on the two clusters. The average dissociation energy barriers are 0.51 eV on the Cu13 cluster and 0.12 eV on the defective graphene-supported Cu13 cluster, which are lowered by ~ 19% and ~ 81% compared with the pristine Cu(111) surface, respectively. Furthermore, compared with the pure Cu13 cluster, the average dissociation energy barrier on the defective graphene-supported Cu13 cluster is substantially reduced by about 76%. The preferred dissociation mechanisms on the two clusters are H2 located at a top-bridge site with the barrier heights of 0.30 eV on the Cu13 cluster and - 0.31 eV on the defective graphene-supported Cu13 cluster. Analysis of the H-Cu bond interactions in the transition states shows that the antibonding-orbital center shifts upwards on the defective graphene-supported Cu13 cluster compared with the one on the Cu13 cluster, which explains the reduction of the dissociation energy barrier. The average adsorption energy of dissociated H atoms is also greatly enhanced on the defective graphene-supported Cu13 cluster, about twice that on pure Cu13.

Theoretical study on the element distribution characteristics and the effects of oxygen in TiZrHfNb high entropy alloys

Short range order and oxygen both have great effects on the mechanical properties like yield strength and ductility of refractory high entropy alloys. In this work, we studied the element distribution characteristics and oxygen occupation properties in TiZrHfNb high-entropy alloy based on first principles, molecular dynamics and Monte Carlo calculations. Two thousands of TiZrHfNb crystal models were firstly calculated based on first principles calculations to analyze the element distribution characteristics. The Warren-Cowley parameters were then evaluated, the Nb-Nb and Ti-Zr atomic pairs tend to form in TiZrHfNb. Hybrid of molecular dynamics and Monte Carlo calculations at 300 K and 1000 K are further carried out to study the possible short range order and phase transition in TiZrHfNb. The element distributions are not uniform, and the transition from body-centered cubic to hexagonal close packed structures are observed. The oxygen atoms are then placed into the enriched regions of Ti, Zr, Hf, and Nb in high-entropy alloy, respectively. The ab initio molecular dynamics calculations of these four configurations are carried out and the diffusion coefficients are evaluated. The oxygen owns the largest diffusion coefficient in the Nb-rich zone. Furthermore, the tensile simulations reveal the great effects of element distributions and oxygen occupations on the mechanical properties of TiZrHfNb. These findings will help us to understand the short range order characteristic and oxygen occupation effects on the phase stability and to regulate the mechanical properties of TiZrHfNb high-entropy alloy.

A Complementary Experimental and Theoretical Approach for Probing the Surface Functionalization of ZnO with Molecular Catalyst Linkers

AbstractThe application of ZnO materials as solid‐state supports for molecular heterogeneous catalysis is contingent on the functionalization of the ZnO surface with stable self‐assembled monolayers (SAMs) of catalyst linker molecules. Herein, experimental and theoretical methods are used to study SAMs of azide‐terminated molecular catalyst linkers with two different anchor groups (silane and thiol) on poly and monocrystalline (0001, ) ZnO surfaces. Angle‐resolved and temperature‐dependent X‐ray photoelectron spectroscopy (XPS) is used to study SAM binding modes, thermal stabilities, and coverages. The binding strengths and atomistic ordering of the SAMs are determined via atom‐probe tomography (APT). Density functional theory (DFT) and ab initio molecular dynamics (AIMD) calculations provide insights on the influence of the ZnO surface polarity on the interaction affinity and conformational behavior of the SAMs. The investigations show that SAMs based on 3‐azidopropyltriethoxysilane possess a higher binding strength and thermal stability than the corresponding thiol. SAM surface coverage is strongly influenced by the surface polarity of ZnO, and the highest coverage is observed on the polycrystalline surface. To demonstrate the applicability of linker‐modified polycrystalline ZnO as a catalyst support, a chiral Rh diene complex is immobilized on the azide‐terminal of the SAM and its coverage is evaluated via XPS.

Origin of the Unusual High Optical Nonlinearities Observed in Glassy Chalcogenides

AbstractNonlinear photonics integrated at the chip scale opens the path to new applications in an increasing number of fields such as all‐optical computing, high bit rate communications on chip, or embedded sensing with frequency combs and super‐continuum sources. All these applications require materials having the best trade‐off between optical losses, Kerr refractive index, and compatibility with current nanofabrication facilities. Although optimizing the nanofabrication process can minimize linear optical losses to some extent, optimizing the Kerr index of the materials remains challenging because a clear understanding of the link between atomic structure and optical nonlinearities is still missing. This is precisely what this work addresses for chalcogenide glasses based on thin films of Ge‐Sb‐Se alloys, a promising class of materials fully compatible with large‐scale integration technology from the microelectronics industry. By coupling nonlinear Kerr index metrology with ab initio molecular dynamics calculations of amorphous models, this work unveils the unique molecular patterns in these alloys that are responsible for their unusual nonlinear polarizability. This provides for the first time valuable rules for the design of new optical materials with improved Kerr index enabling miniaturization and implementation of future nonlinear photonic devices that can then operate at significantly lower power.

Density‐modified structure and mechanical properties of amorphous Si2BC3N by ab initio molecular dynamics calculations

AbstractDensity‐modified structural features and mechanical properties of the amorphous Si2BC3N are studied by ab initio molecular dynamics simulations. The chemical bonds of Si2BC3N are insensitive to the density variation, which is reflected by the negligible changes in bond lengths, peak locations in density of states and Bader charge values under different densities. Instead, the composition of chemical bonds is altered. Meanwhile, high‐density condition induces the transition of polyhedral units from the sp2‐like trigonal configuration to the tetrahedral configuration, especially for B, C, and N. This variation is the main structural responding mechanism of Si2BC3N to increased density, which is different from the stretching and/or shrinkage of bonds as occurred in crystals. The increased tetrahedron content shall further benefit the amorphous structure stability of Si2BC3N by impeding the separation of turbostratic BN(C), and enhance the second‐order elastic constants, elastic moduli and tensile/shear strengths of Si2BC3N. The high density may decrease the debonding capability of the fiber/Si2BC3N interface but will not change the preference for crack deflection at interfaces. These results suggest the promising prospect of mechanical property optimization of SiBCN ceramics through density tailoring in experiments.

Dynamics of Hydrogen Bond Breaking Induced by Outer-Valence Intermolecular Coulombic Decay

The photoexcitation of weakly bound complexes can lead to several decay pathways, depending on the nature of the potential energy surfaces. Upon excitation of a chromophore in a weakly bound complex, ionization of its neighbor upon energy transfer can occur due to a unique relaxation process known as intermolecular Coulombic decay (ICD), a phenomenon of renewed focus owing to its relevance in biological systems. Herein, we report the evidence for outer-valence ICD induced by multiphoton excitation by near-ultraviolet radiation of 4.4 eV photons, hitherto unknown in molecular systems. In the binary complexes of 2,6-difluorophenylacetylene with aliphatic amines, a resonant two-photon excitation localized on the 2,6-difluorophenylacetylene chromophore results in the formation of an amine cation following an outer-valence ICD process. The unique trends in experimentally observed translational energy distribution profiles of the amine cations following hydrogen bond dissociation, analyzed with the help of electronic structure and ab initio molecular dynamics calculations, revealed the presence of a delicate interplay of roaming dynamics, methyl-rotor dynamics, and binding energy.

Metallized HOT-graphene: A novel reversible hydrogen storage medium with ultrahigh capacity

By performing first-principles calculations, we have researched the hydrogen storage capability of the alkali metals (Li, Na, K) and alkali-earth metal (Ca) decorated HOT graphene, a novel excellent Dirac semimetal which consists of hexagon, octagon and tetragon carbon rings. Metal Li, Na, K and Ca can be strongly bonded on HOT graphene with very large binding energy instead of forming clusters. Each metal can absorb maximum of 3, 5, 5 and 6 H2, respectively, and the average adsorption energy are all in the reversible hydrogen storage range. In the case of double-sided adsorption, 16 metals can be loaded on 2 × 2 × 1 supercell of HOT graphene and then come into being gravimetric H2 uptake of 12.34 wt%, 14.59 wt%, 11.83 wt% and 13.71 wt% for Li, Na, K and Ca decorated HOT graphene, separately, which significantly exceeds the DoE standard (6.5 wt%). The analysis of the calculated electronic density of states and charge transfer indicates that the strong bonding between metal atoms and HOT graphene is derived from orbital interaction concerning charge transfer, while the adsorption of hydrogen molecule attributes to the polarization of hydrogen molecule near ionized metal atoms and thus electrostatic and van der Waals interactions render H2 to adsorb in the metal atoms. Finally, the integrity of metal decorated HOT graphene based on ab-initio molecular dynamics (AIMD) calculation at corresponding H2 desorption temperatures indicates that the feasibility of practical application of metallized HOT-graphene system as reversible hydrogen storage medium with ultrahigh capacity. And these findings could be expected to facilitate experimental studies.

S 2 − and S3− radicals and the S42− polysulfide ion in lazurite, haüyne, and synthetic ultramarine blue revealed by resonance Raman spectroscopy

Abstract Taking advantage of the Raman resonance effect, we employed 405 and 532 nm excitations to (1) identify sulfur species present in lazurite, haüyne, and synthetic ultramarine blue pigments and (2) investigate the enigmatic ~485 cm–1 band found previously in Raman spectra of lazurite and haüyne collected with 458 nm excitation. In spectra of lazurite and haüyne, bands of the sulfate ion and S2− and S3− radicals can be seen. Spectra collected using 405 nm excitation show the enhancement of the intensity of ν1(S2−) band and its nν1 (n ≤ 7) progression. Spectra collected using 532 nm incident light show the enhancement of intensity of ν1(S3−), ν2(S3−), and ν3(S3−) bands and the nν1 (n ≤ 9) and ν2 + nν1 progressions of the ν1(S3−) band. In spectra collected with 405 nm excitation, we also found features that we ascribe to the S42− polysulfide ion. These include the ν1 symmetric S-S stretching band at ~481 cm–1, the ν2 symmetric S-S stretching band at ~443 cm–1 (only present in spectra of some lazurite samples), the ν3 symmetric S-S bending at 223 cm–1 and the nν1 (n ≤ 5) and nν1+ν3 progressions of the ν1(S42−) band. We observed that under laser illumination, the S42− polysulfide ion rapidly decomposes into two S2− radicals in lazurite while it remains stable in haüyne. In spectra of synthetic ultramarine blue pigments, only features of S2− and S3− radicals were observed. Finally, we verified the identity of the radical and polysulfide ions with ab initio molecular dynamics calculations. We conclude that Raman resonance spectroscopy is a powerful qualitative method to detect polysulfide and sulfur radical species with concentrations below the detection limit of conventional analytical techniques. Owing to the high stability of S42− in haüyne, this mineral structure appears promising as a host material for S42− entrapment, making it potentially useful for applications in optoelectronics.

Exploring the feasibility of monolayer Mg2N as an anode material for alkali metal ion batteries: A first principle calculation

To meet the growing demand for energy storage devices, anode material with good electrochemical performance is urgently needed. In view of the lighter anode material contributing to high specific capacity, this study examines the feasibility of Mg2N monolayer as an anode material for alkali metal ion batteries based on the first principle calculations. A comprehensive study was carried out which includes the stability, electronic properties and electrochemical performance for Li/Na/K-ion batteries (LIBs/NIBs/KIBs). The results of phonopy spectrum and ab initio molecular dynamics (AIMD) calculations demonstrated that monolayer Mg2N possesses high dynamic and thermal stability. The electronic band structure and density of states indicated the superior conductivity of Mg2N, ideal for the use of electrode material. The calculation of electrochemical performance revealed that Mg2N exhibits ultra-high theoretical specific capacities of 2140 mAh g−1 and 863 mAh g−1 as an anode material for LIBs and NIBs that far surpass the specific capacities of graphite. The low diffusion barrier (both below 0.01 eV for LIBs/NIBs) ensures fast ion transport during the charging/discharging process. The aforementioned results suggested that Mg2N shows the potential as a promising anode material for LIBs and NIBs. This work may guide the design of anode material for alkali metal ion batteries.

Quantifying the partial ionization effect of gold in the transition region between condensed matter and warm dense matter

It is now well known that solids under ultra-high-pressure shock compression will enter the warm dense matter (WDM) regime which connects condensed matter and hot plasma. How condensed matter turns into the WDM, however, remains largely unexplored due to the lack of data in the transition pressure range. In this letter, by employing the unique high-Z three-stage gas gun launcher technique developed recently, we compress gold into TPa shock pressure to fill the gap inaccessible by the two-stage gas gun and laser shock experiments. With the aid of high-precision Hugoniot data obtained experimentally, we observe a clear softening behavior beyond ~560 GPa. The state-of-the-art ab-initio molecular dynamics calculations reveal that the softening is caused by the ionization of 5d electrons in gold. This work quantifies the partial ionization effect of electrons under extreme conditions, which is critical to model the transition region between condensed matter and WDM.

Two-dimensional [formula omitted] (X = Si, Ge; Y = S, Se, Te) family with potential application in photocatalysis

Photocatalysis is an attractive route for energy harvesting and pollution mitigation, however, designing an optimal catalyst is rather challenging. Motivated by fundamental interest and potential applications, the investigations of two-dimensional (2D) photocatalyst are important subjects in solar energy conversion. In this work, the stability, electronic, and optical properties of 2D Cr2X2Y6 (X = Si, Ge; Y = S, Se, Te) family are investigated to explore their photocatalytic activity for water splitting. Density functional theory (DFT) and ab-initio molecular dynamics (AIMD) calculations were employed. The electronic band structure calculations indicate that all these monolayers, except Cr2Ge2Te6 and Cr2Si2Te6, have an adequate bandgap, as well as suitable band-edge positions for photocatalytic water splitting reactions, specifically under acidic conditions. Moreover, the studied materials show strong capability of harvesting sunlight, that is essential for photocatalytic activity. Remarkably, Cr2Ge2Se6 and Cr2Si2Se6 monolayers exhibited high solar-to-hydrogen energy conversion efficiencies of 14.89% and 13.26%, respectively. The presented results pave the way for designing other electronically optimized layered photocatalysts for water splitting.

Ab initio molecular dynamics calculation and vacuum distillation experimental study on the interaction mechanism of PbS–FeS

An important way to obtain PbS and FeS is the thermal decomposition of Jamesonite. However, the mechanism of PbS–FeS interaction is unknown. In order to explore the separation effect of PbS and FeS, thermodynamic calculation, dynamic simulation and vacuum distillation experiments were used to explore the interaction mechanism of PbS and FeS. The decomposition and volatilization temperatures of PbS and FeS were obtained by thermodynamic calculation. The difference of saturated vapor pressure indicates that there is a tendency of separation between them. The ab initio molecular dynamics method was used to calculate the density of states of PbS and FeS at different temperatures, indicating that the FeS(114) structure is more stable than the PbS(200) structure, and the Pb–S bond is easier to break than the Fe–S bond at the same temperature. The experimental results of vacuum distillation show that the volatilization temperature of PbS is much lower than that of FeS, and FeS can only volatilize into the gas phase at a higher temperature. The theoretical calculation method is consistent with the experimental results, which shows that the thermodynamic calculation and dynamic simulation methods are reliable in predicting the volatilization and separation of crystal structures. The interaction mechanism between PbS and FeS was explored from the theoretical point of view to provide theoretical guidance for vacuum distillation experiment.

Ultralow lattice thermal conductivity, negative thermal expansion, elastic and thermoelectric properties of Lanthanum Nitride: Insights from first-principle calculations

Ultralow lattice thermal conductivity, negative thermal expansion and thermoelectric properties for the face centered cubic phase of lanthanum nitride (LaN) have been explored for the first time from first-principle density functional theory and ab-initio molecular dynamics calculations. The elastic constants, phonon dispersion relations, mode Grüneisen parameter, phonon group velocity and phonon-phonon scattering rates have been studied to unveil the ultralow lattice thermal conductivity ( = 1.08 Wm−1K−1) of the compound at room temperature (T = 300 K). The negative thermal expansion of LaN has been estimated from the mode Grüneisen parameter. The electronic band structure, hole-electron effective masses and the thermoelectric properties including the Seebeck coefficient, electrical conductivity, electronic thermal conductivity and thermoelectric power factor have been investigated to estimate the high thermoelectric figure of merit (ZT ∼ 0.98) of the system at room temperature. We believe that the present study will help to unfold LaN for its applications in thermoelectric power generators, fibre-optic communications, fuel cells and in clean and global energy conservation.

Enhanced Thermoelectric Performance of Nanostructured Cu2SnS3 (CTS) via Ag Doping

The present work aims to investigate the effect of Ag doping on the thermoelectric properties of Cu2SnS3 (CTS). Various Cu2Ag(x)Sn(1–x)S3 (0.05 ≤ x ≤ 0.25) samples were synthesized by mechanical alloying followed by spark plasma sintering, and their structural and transport properties were systematically investigated. The x = 0.15 sample presented a ∼10-fold higher power factor than the undoped CTS. Although, the x = 0.125 sample had a lower power factor than the x = 0.15 sample, owing to its lower thermal conductivity, both the samples showed the highest zT ∼ 0.8 at 723 K. This value is comparable to the best results available in the literature for earth-abundant and eco-friendly thermoelectric materials. Interestingly, the thermal conductivity of Cu2Ag(x)Sn(1–x)S3 samples increased with Ag substitution, which was further investigated using the first-principles and ab initio molecular dynamics calculations. It was observed that the incorporation of Ag into the system decreases the root mean square displacement of the other cations and anions, reducing the scattering of phonons and thereby increasing the lattice thermal conductivity. Moreover, the calculations on the formation energy have revealed the reason for the structural transformation of CTS and similar diamond-like structures toward high symmetry polymorphs by external doping. The increase in zT is directly related to the optimization of the band gap and the weighted mobility, which have been investigated experimentally and using the first principle method.

C-C Bond Formation Reaction Catalyzed by a Lithium Atom: Benzene-to-Biphenyl Coupling.

Transition-metal-catalyzed carbon-carbon (C-C) bond formation is an important reaction in pharmaceutical and organic chemistry. However, the reaction process is composed of multiple steps and is expensive owing to the presence of transition metals. This study proposes a lithium-catalyzed C-C coupling reaction of two benzene molecules (Bz) to form a biphenyl molecule, which is a transition-metal-free reaction, based on ab initio and direct ab initio molecular dynamics (AIMD) calculations. The static ab initio calculations indicate that the reaction of two Bz molecules with Li- ions (reactant state, RC) can form a stable sandwiched complex (precomplex), where the Li- ion is sandwiched by two Bz molecules. The complex formation reaction can be expressed as 2Bz + Li - → Bz(Li -)Bz, where the C-C distance between the Bz rings is 2.449 Å. This complex moves to the transition state (TS) via the structural deformation of Bz(Li-)Bz, where the C-C distance is shortened to 2.118 Å. The barrier height was calculated to be -9.9 kcal/mol (relative to RC) at the MP2/6-311++G(d,p) level. After TS, the C(sp3)-C(sp3) single bond was completely formed between the Bz rings (the C-C bond distance was 1.635 Å) (late complex). After the dissociation of H2 from the late complex, a biphenyl molecule was formed: the C(sp2)-C(sp2) bond. The calculations suggest that the C-C bond coupling of Bz occurred spontaneously from 2Bz + Li-, and biphenyl molecules were directly formed without an activation barrier. Direct AIMD calculations show that the C-C coupling reaction also takes place under electron attachment to Li(Bz)2: Li(Bz)2 + e- → [Li-(Bz)2]ver → precomplex → TS → late complex, where [Li-(Bz)2]ver is the vertical electron capture species of Li(Bz)2. Namely, the C-C coupling reaction spontaneously occurred in Li(Bz)2 owing to electron attachment. Similar C-C coupling reactions were also observed for halogen-substituted benzene molecules (Bz-X, X = F and Cl). Furthermore, this study discusses the mechanism of C-C bond formation in electron capture based on the theoretical results.

In situ formation of stable solid electrolyte interphase with high ionic conductivity for long lifespan all-solid-state lithium metal batteries

Parasitic reactions inevitably occur at the interface of lithium (Li) metal and polymer electrolytes due to ultrahigh Li reducibility coupled with poor interfacial stability or ionic conductivity. This leads to significant capacity loss and inferior lifespan of Li metal batteries (LMBs). Herein, we engineered a stable solid electrolyte interphase (SEI) layer at the interface of Li metal and polyethylene oxide (PEO) electrolyte via incorporation of phosphazene molecules. The phosphazene-solid polymer electrolyte (P-SPE) shows a significantly higher long-term stability against Li metal anode when compared with non-modified SPE. Using cryogenic transmission electron microscopy (cryo-TEM) and X-ray photon spectroscopy (XPS), Li3N, LiF, Li3P and Li3PO4 nanocrystals were identified in the SEI layer. The Li|Li cell with P-SPE cycle for 1800 cycles at 0.2 mA cm‒2. The Li||LFP cells with P-SPE deliver a specific capacity of ∼150 mAh g−1 and ∼120 mAh g−1 at 1C and 2C charge/discharge rates, respectively, with up to 80% capacity retention after 500 and 1000 cycles, respectively. Critical role of phosphazene-modified SEI in improving electrochemical performance is further investigated by density function theory (DFT) and ab-initio molecular dynamic (AIMD) calculations. This study offers a promising approach for engineering a stable and ion-conductive Li|polymer electrolyte interface for long lifespan LMBs.