The atomistic understanding of solid electrolytes is essential for advancing solid-state batteries and enabling their large-scale commercialisation. Whilst the importance of external pressure in the manufacturing and operation of practical solid-state batteries has been clearly recognised, its impact on the fundamental properties of solid electrolytes remains underexplored. Here, we combine density functional theory and ab initio molecular dynamics simulations to investigate the effect of pressure (0−10 GPa) on the structural, electronic and ion transport properties of lithium argyrodite solid electrolytes Li 6 PS 5 X (X = Cl and/or Br) with different levels of halide mixing and anion site (S 2 ⁻/X⁻) disorder. We show that increased pressure induces systematic decreases in lattice volume and stability for both ordered and disordered systems. Anion disorder narrows the bandgap, which can change dramatically as a function of pressure. The Li-ion conductivities (~ 0.54−1.05 S cm⁻ 1 at 600 K) and activation energies (< 0.16 eV), remain high and low, respectively, up to ~ 2 GPa, with particularly pressure-resilient conduction networks observed in the mixed halide and disordered structures. At higher pressures (> 2 GPa), most compositions show a clear increase in activation energy (0.15−0.42 eV) accompanied by reduced conductivity (~ 0.12−0.59 S cm⁻ 1 at 600 K). These findings establish external pressure, site disorder and halide mixing as interdependent parameters that can be used to tune argyrodite solid electrolytes for high-performance solid-state batteries.

In this paper we build on previous work to characterise a new phase with stoichiometry Li3(OH)2Br existing between ∼225 degC and ∼275 degC in the LiBr-LiOH phase diagram. Diffraction studies indicate that the phase takes a hexagonal unit cell, and theoretical mod- elingisusedtosuggestapossiblecrystalstructure. Nuclearmagneticresonancespectroscopy and electrochemical impedance spectroscopy measurements demonstrate excellent lithium- ion dynamics in this phase, with an ionic conductivity of 0.12 S/cm at 250 degC. Initial attempts to stabilise this phase at room temperature through quenching were not successful. 1 Instead, a metastable state demonstrating poor lithium-ion conductivity is found to form. This is an important consideration for the synthesis of Li2OHBr solid-state electrolytes (also found in the LiBr-LiOH phase diagram) which are synthesised by cooling through phase fields containing Li3(OH)2Br, and are hence susceptible to these impurities.

Amorphous solid-state electrolytes (SSEs) play a pivotal role as fundamental components within all-solid-state lithium batteries, yet their understanding lags behind that of crystalline materials. In this work, a novel amorphous SSE 5Li2S-3SiS2 (mol %) with a high ionic conductivity of 1.2 mS cm-1 is first reported. The silicon and sulfur atoms in the edge-sharing Si2S64- are less attracted to lithium compared to the SiS44- anion, which is expected to facilitate the lithium ions conduction in SSEs. More importantly, the relationship between the material properties and local structure in the amorphous thiosilicate SSEs is revealed, particularly highlighting the desirable edge-sharing local structure. The Si2S64- presents better stability with Li metal. This work offers an important guideline in the development of anion frameworks in amorphous sulfide SSEs for high-performance all-solid-state lithium metal batteries. A novel amorphous SSE 5Li2S-3SiS2 (mol %) with a high ionic conductivity of 1.2 mS cm-1 is reported. The silicon and sulfur atoms in the edge-sharing Si2S64- are less attracted to lithium compared to the SiS44- anion, which is expected to facilitate the lithium ions conduction in SSEs. More importantly, the Si2S64- indicates better stability with Li metal is revealed. image

Antiperovskites are generating considerable interest as potential solid electrolyte materials for solid-state batteries because of their promising ionic conductivity, wide electrochemical windows, stability, chemical diversity and tunability, and low cost. Despite this, there is a surprising lack of a systematic study of antiperovskite surfaces and their influence on the performance of these materials in energy storage applications. This is rectified here by providing a comprehensive density functional theory investigation of the surfaces of M3OX (M = Li or Na; X = Cl or Br) antiperovskites. Specifically, we focus on the stability, electronic structure, defect chemistry, and ion transport properties of stable antiperovskite surfaces and how these contribute to the overall performance and suitability of these materials as solid electrolytes. The findings presented here provide critical insights for the design of antiperovskite surfaces that are both stable and promote ion transport in solid-state batteries.

Understanding diffusion mechanisms in solid electrolytes is crucial for advancing solid-state battery technologies. This study investigates the role of structural disorder in Li7-x PS6-x Br x argyrodites using ab initio molecular dynamics, focusing on the correlation between key structural descriptors and Li-ion conductivity. Commonly suggested parameters, such as configurational entropy, bromide site occupancy, and bromine content, correlate with Li-ion diffusivity but do not consistently explain conductivity trends. We find that a uniform distribution of bromine and sulfur ions across the 4a and 4d sublattices is critical for achieving high conductivity by facilitating optimal lithium jump activation energies, anion-lithium distances, and charge distribution. Additionally, we introduce the ionic potential as a simple descriptor that predicts argyrodite conductivity by assessing the interaction strength between cations and anions. By analyzing the correlation between ionic potential and conductivity for a range of argyrodite compositions published over the past decade, we demonstrate its broad applicability. Minimizing and equalizing ionic potentials across both sublattices enhances conductivity by reducing the strength of anion-lithium interactions. Our analysis of local environments coordinating Li jumps reveals that balancing high and low-energy pathways is crucial for enabling macroscopic diffusion, supported by investigating percolating pathways. This study highlights the significance of the anionic framework in lithium mobility and informs the design of solid electrolytes for improved energy storage systems.

A new calcium-based Room temperature Stable Electride (RoSE), K[{Ca[N(Mes)(SiMe3)]3(e-)}2K3] (2), is successfully synthesized from the reaction of a calcium tris-amide, [Ca{N(Mes)(SiMe3)}3K] (1) (Mes = 2,4,6-trimethylphenyl), with potassium under mechanochemical treatment. The dimeric structure of K[{Ca[N(Mes)(SiMe3)]3(e-)}2K3] is calculated using ab initio random structure searching (AIRSS) methods. This shows the existence of highly localized anionic electrons (e-) and suggests poor electrical conductance, as confirmed via electroconductivity measurements. The two anionic electrons in 2 are strongly antiferromagnetically coupled, thus in agreement with the largely diamagnetic response from magnetometry. Reaction of 2 with pyridine affords 4,4'-bipyridine, while reaction with benzene gives C-H activation and formation of a calcium hydride complex, [K(η6-C6H6)4][{Ca[N(Mes)(SiMe3)](H)}2K3] (3). Computational DFT analysis reveals the crucial role played by the ligand framework in the stabilization of this new Ca-hydride complex.

A prerequisite for the realization of solid-state batteries is the development of highly conductive solid electrolytes. Li3PS4 is the archetypal member of the highly promising thiophosphate family of Li-ion conductors. Despite a multitude of investigations into this material, the underlying atomic-scale features governing the roles of and the relationships between cation and anion dynamics, in its various temperature-dependent polymorphs, are yet to be fully resolved. On this basis, we provide a comprehensive molecular dynamics study to probe the fundamental mechanisms underpinning fast Li-ion diffusion in this important solid electrolyte material. We first determine the Liion diffusion coefficients and corresponding activation energies in the temperature-dependent gamma, beta, and alpha polymorphs of Li3PS4 and relate them to the structural and chemical characteristics of each polymorph. The roles that both cation correlation and anion libration play in enhancing the Li-ion dynamics in Li3PS4 are then isolated and revealed. For gamma- and beta-Li3PS4, our simulations confirm that the interatomic Li-Li interaction is pivotal in determining (and restricting) their Li-ion diffusion. For alpha-Li3PS4, we quantify the significant role of Li-Li correlation and anion dynamics in dominating Li-ion transport in this polymorph for the first time. The fundamental understanding and analysis presented herein is expected to be highly applicable to other solid electrolytes where the interplay between cation and anion dynamics is crucial to enhancing ion transport.

All-solid-state lithium metal batteries can address crucial challenges regarding insufficient battery cycling life and energy density. The demonstration of long-cycling dendrite-free all-solid-state lithium metal batteries requires precise tailoring of lithium-ion transport of solid-state electrolytes (SSEs). In this work, a proof of concept is reported for precise tailoring of lithium-ion transport of a halide SSE, Li3InCl6, including intragranular (within grains) but also intergranular (between grains) lithium-ion transport. Lithium-ion migration tailoring mechanism in crystals is developed by unexpected enhanced Li, In, and Cl vacancy populations and lower energy barrier for hopping. The lithium-ion transport tailoring mechanism between the grains is determined by the elimination of voids between grains and the formation of unexpected supersonic conducting grain boundaries, boosting the lithium dendrite suppression ability of SSE. Due to boosted lithium-ion conduction and dendrite-suppression ability, the all-solid-state lithium metal batteries coupled with Ni-rich LiNi0.83Co0.12Mn0.05O2 cathodes and lithium metal anodes demonstrate breakthroughs in electrochemical performance by achieving extremely long cycling life at a high current density of 0.5 C (2000 cycles, 93.7% capacity retention). This concept of precise tailoring of lithium-ion transport provides a cost, time, and energy efficient solution to conquer the remaining challenges in all-solid-state lithium-metal batteries for fast developing electric vehicle markets.

Nonradiative recombination leads to losses in efficiency in optoelectronic devices such as photovoltaic cells and light-emitting diodes. Charges trapped at point defects or self-trapped as a small polaron may act as recombination centers. Using various phases of titanium dioxide as an example, we provide first-principles predictions that small hole polarons in the bulk of the crystal would exhibit significant rates of recombination with electrons in the conduction band. However, small hole polarons trapped at a model grain boundary are predicted to have much higher nonradiative recombination rates, which can be attributed to softer phonon modes in the vicinity of the boundary as well as greater electron-phonon coupling. These findings have ramifications in materials other than titanium dioxide, and we propose strategies to reduce the degree of recombination that would occur at grain boundaries.

Although polycrystalline solid electrolytes are central to the utilization of solid- state batteries with lithium metal anodes, lithium dendrite formation and reduced Li-ion conductivity at their grain boundaries remain primary concerns. Given that experimental studies on polycrystalline materials are notoriously difficult to perform and interpret, computational techniques are invaluable for providing insight at the atomic scale. Here, we carry out first-principles calculations on representative grain boundaries in three important Li-based solid electrolyte families, namely, an anti-perovskite oxide, Li3OCl, a thiophosphate, Li3PS4, and a halide, Li3InCl6, to demonstrate the significantly different impacts that grain boundaries have on their electronic structure, ion conductivity and correlated ion transport. Our results show that even when grain boundaries do not significantly impact ionic conductivity, they can still strongly perturb the electronic structure and contribute to undesirable electrical conductivity and potential lithium dendrite propagation. We also illustrate, for the first time, how cor- related motion, including the so-called paddle-wheel mechanism, which has so far only been considered for the bulk, can vary substantially at grain boundaries. Our findings reveal the dramatically different behaviour of solid electrolytes at the grain boundary compared to the bulk and its potential consequences and benefits for the design of solid-state batteries.

The fluoride ionbattery (FIB) is a promising post-lithium ionbattery chemistry owing to its high theoretical energy density andthe large elemental abundance of its active materials. Nevertheless,its utilization for room-temperature cycling has been impeded by theinability to find sufficiently stable and conductive electrolytesat room temperature. In this work, we report the use of solvent-in-saltelectrolytes for FIBs, exploring multiple solvents to show that aqueouscesium fluoride exhibited sufficiently high solubility to achievean enhanced (electro)-chemical stability window (3.1 V) that couldenable high operating voltage electrodes, in addition to a suppressionof active material dissolution that allows for an improved cyclingstability. The solvation structure and transport properties of theelectrolyte are also investigated using spectroscopic and computationalmethods.

In this work, we report the synthesis of a room-temperature-stable electride (RoSE) reagent, namely K+(LiHMDS)e- (1) (HMDS: 1,1,1,3,3,3-hexamethyldisilazide), from accessible starting mate-rials (potassium metal and LiHMDS) via mechanochemical ball mill-ing at 20 mmol scale. Despite its amorphous nature, the presence of anionic electrons in 1, key diagnostic criteria for an electride, was confirmed by both experimental and computational studies. Therefore, by definition, 1 is an electride. Utilizing its anionic elec-trons, electride reagent 1 exhibited a versatile reactivity profile that includes (1) mediation of C-H activation and C-C coupling of benzene and pyridine and (2) mediation of solvent-free Birch reduc-tion. This work proves the concept of facile mechanochemical syn-thesis of a room-temperature-stable electride, and it introduces electride 1 to the synthetic chemistry community as a versatile re-agent.

Multidentate neutral amine ligands play vital roles in coordination chemistry and catalysis. In particular, these ligands are used to tune the reactivity of Group-1 metal reagents, such as organolithium reagents. Most, if not all, of these Group-1 metal reagent-mediated reactions occur in solution. However, the solution-state coordination behaviors of these ligands with Group-1 metal cations are poorly understood, compared to the plethora of solid-state structural studies based on single-crystal X-ray diffraction (SCXRD) studies. In this work, we comprehensively mapped out the coordination modes with Group-1 metal cations for three multidentate neutral amine ligands: tridentate 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3TACN), tetradentate tris[2-(dimethylamino)ethyl]amine (Me6Tren), and hexadentate N,N',N″-tris-(2-N-diethylaminoethyl)-1,4,7-triaza-cyclononane (DETAN). The macrocycles in the Me3TACN and DETAN are identified as the rigid structural directing motif, with the sidearms of DETAN providing flexible "on-demand" coordination sites. In comparison, the Me6Tren ligand features more robust coordination, with the sidearms less likely to undergo the decoordinating-coordinating equilibrium. This work will provide a guidance for coordination chemists in applying these three ligands, in particular, the new DETAN ligand to design metal complexes which suit their purposes.

Understanding charge-carrier transport in semiconductors is vital to the improvement of material performance for various applications in optoelectronics and photochemistry. Here, we use hybrid density functional theory to model small hole polaron transport in the anatase, brookite, and TiO2-B phases of titanium dioxide and determine the rates of site-to-site hopping as well as thermal ionization into the valance band and retrapping. We find that the hole polaron mobility increases in the order TiO2-B < anatase < brookite and there are distinct differences in the character of hole polaron migration in each phase. As well as having fundamental interest, these results have implications for applications of TiO2 in photocatalysis and photoelectrochemistry, which we discuss.

Polycrystalline anatase titanium dioxide has drawn great interest, because of its potential applications in high-efficiency photovoltaics and photocatalysts. There has been speculation on the electronic properties of grain boundaries but little direct evidence, because grain boundaries in anatase are challenging to probe experimentally and to model. We present a combined experimental and theoretical study of anatase grain boundaries that have been fabricated by epitaxial growth on a bicrystalline substrate, allowing accurate atomic-scale models to be determined. The electronic structure in the vicinity of stoichiometric grain boundaries is relatively benign to device performance but segregation of oxygen vacancies introduces barriers to electron transport, because of the development of a space charge region. An intrinsically oxygen-deficient boundary exhibits charge trapping consistent with electron energy loss spectroscopy measurements. We discuss strategies for the synthesis of polycrystalline anatase in order to minimize the formation of such deleterious grain boundaries.

First-principles calculations of the electronic structure of reduced anatase TiO2 nanoparticles are performed using a hybrid density functional theory approach for an accurate description of charge trapping. It is found that, in the bulk and at extended surfaces, electrons introduced by oxygen vacancies delocalize but, in reduced nanoparticles, electrons preferentially localize (forming Ti3+ species) at low-coordinated sites on the surface of the particle. It is favorable for nanoparticles to be oxygen-deficient in oxygen-poor conditions with the Ti33O66 nanoparticle being significantly easier to reduce than the larger Ti151O302 nanoparticle. Since low-coordinated sites are more prevalent in smaller nanoparticles, this suggests that there is a delicate balance between the number of carriers introduced by vacancies and the number of trapped electrons.

First‐principles calculations of the electronic structure and charge‐trapping behavior of Σ3 {112} and Σ1 {110} twin boundaries (TBs) in anatase TiO 2 are performed using an accurate hybrid density functional theory approach. The former is characterized experimentally using transmission electron microscopy (TEM) and very good agreement on the structure is found. The {110} twin has not yet been observed but TEM and scanning tuneling microscopy (STM) image simulations are presented to aid experimental identification. Holes are found to trap in a polaronic configuration at both the twin boundaries. The {112} TB presents more favorable sites for hole polaron formation at the boundary with trapping energies 0.16–0.18eV, more favorable than the bulk. The {110} TB presents hole polaron trapping sites ranging from 0.07 eV, less favorable, to 0.14 eV, more favorable, than the bulk. Neither boundary is found to favor electron trapping, indicating they are relatively benign to the performance of anatase as an n ‐type conductor.