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Constructing an artificial solid electrolyte interphase (SEI) on lithium metal electrodes is a promising approach to address the rampant growth of dangerous lithium morphologies (dendritic and dead Li⁰) and low Coulombic efficiency that plague development of lithium metal batteries, but how Li⁺transport behavior in the SEI is coupled with mechanical properties remains unknown. We demonstrate here a facile and scalable solution-processed approach to form a Li₃N-rich SEI with a phase-pure crystalline structure that minimizes the diffusion energy barrier of Li⁺across the SEI. Compared with a polycrystalline Li₃N SEI obtained from conventional practice, the phase-pure/single crystalline Li₃N-rich SEI constitutes an interphase of high mechanical strength and low Li⁺diffusion barrier. We elucidate the correlation among Li⁺transference number, diffusion behavior, concentration gradient, and the stability of the lithium metal electrode by integrating phase field simulations with experiments. We demonstrate improved reversibility and charge/discharge cycling behaviors for both symmetric cells and full lithium-metal batteries constructed with this Li₃N-rich SEI. These studies may cast new insight into the design and engineering of an ideal artificial SEI for stable and high-performance lithium metal batteries.

 

Dense polymorphs of silica have been demonstrated experimentally to incorporate from 1.5 wt% to as much as 11.6 wt% H₂O as OH groups, with implications for the hydrogen budgets of Earth and other planets. This OH is thought to enter the SiO₂structure via a charge‐balanced substitution in which silicon vacancies (V_Si) are compensated by protonating four of the surrounding six oxygen atoms, often referred to as a hydrogarnet‐type defect. There are many possible configurations for this defect structure in dense silica, but the nature of these configurations and whether they can be distinguished experimentally is unknown. We present here density functional theory calculations that systematically assess the possible configurations of a hydrogarnet‐type defect in stishovite (rutile‐type SiO₂), with direct comparisons to experimental vibrational spectroscopy data. We predict that stishovite synthesized at 450 K and 10 GPa quenched to room temperature is dominated by a single defect type with tetrahedral geometry. This leads to OH stretching modes (2,500–3,000 cm⁻¹) and SiOH bending modes (∼1,400–1,450 cm⁻¹) largely consistent with experimentally observed modes. One remaining issue is that our calculations produce results compatible with experimental data on H to D exchange, but do not explain why a considerable fraction of the 1,420 cm⁻¹mode shifts by only 40 cm⁻¹in deuterated samples. At elevated pressures and temperatures, we find that a second square planar defect configuration also becomes favorable, leading to modes that should allow differentiation from the tetrahedral configuration.

 

Functional unit and organization (FUO) paradigm starts with functional units and assembles these functional units into specific organizations to optimize material performance. An advantage of FUO paradigm is interpretation of physical essence of traditional structure–performance relationships. Experimental achievements based on FUO paradigm abound in recent years, demanding theoretical explanations for further quantitative material design. Following FUO paradigm, here a three‐step model (bond‐region‐structure) of nanotwin (NT) unit and orientation organization to optimize mechanical performance is established. First, anisotropic elasticities of representative bonds and assembled regional elastic constants are evaluated. Second, yield conditions of different regions, which are summarized as critical resolved shear stress (CRSS) criteria of NT structure, are quantified. Third, anisotropic yield strengths of NT structure from the regional elastic constants and CRSS criteria are derived. This FUO‐based model is implemented into InSb, GaAs, and ZnS, predicted elastic constants and yield strengths are validated with molecular dynamics (MD) simulations. The method is more efficient than MD with comparable accuracy, and is also flexible to combine with density function theory and experiment. This demonstration sets foundation of NT unit and orientation organization design for achieving optimum mechanical performance.

 

A molten metal is an atomic liquid that lacks directional bonding and is free from chemical ordering effects. Experimentally, liquid metals can be undercooled by up to ∼20% of their melting temperature but crystallize rapidly in subnanosecond time scales at deeper undercooling. To address this limited metastability with respect to crystallization, we employed molecular dynamics simulations to study the thermodynamics and kinetics of the glass transition and crystallization in deeply undercooled liquid Ag. We present direct evidence that undercooled liquid Ag undergoes a first-order configurational freezing transition from the high-temperature homogeneous disordered liquid phase (L) to a metastable, heterogeneous, configura-tionally ordered state that displays elastic rigidity with a persistent and finite shear modulus, μ. We designate this ordered state as the G-phase and conclude it is a metastable non-crystalline phase. We show that the L−G transition occurs by nucleation of the G-phase from the L-phase. Both te L- and G-phases are metastable because both ultimately crystallize. The observed first-order transition is reversible: the G-phase displays a first-order melting transition to the L-phase at a coexistence temperature, TG,M. We develop a thermodynamic description of the two phases and their coexistence boundary.