First-principles calculation of the pressure dependence of phase equilibria in the Al-Li system

Ultrahigh-current density anodes with interconnected Li metal reservoir through overlithiation of mesoporous AlF3 framework

Lithium (Li) metal is the ultimate solution for next-generation high-energy density batteries but is plagued from commercialization by infinite relative volume change, low Coulombic efficiency due to side reactions, and safety issues caused by dendrite growth. These hazardous issues are further aggravated under high current densities needed by the increasing demand for fast charging/discharging. We report a one-step fabricated Li/Al₄Li₉-LiF nanocomposite (LAFN) through an "overlithiation" process of a mesoporous AlF₃ framework, which can simultaneously mitigate the abovementioned problems. Reaction-produced Al₄Li₉-LiF nanoparticles serve as the ideal skeleton for Li metal infusion, helping to achieve a near-zero volume change during stripping/plating and suppressed dendrite growth. As a result, the LAFN electrode is capable of working properly under an ultrahigh current density of 20 mA cm^-2 in symmetric cells and manifests highly improved rate capability with increased Coulombic efficiency in full cells. The simple fabrication process and its remarkable electrochemical performances enable LAFN to be a promising anode candidate for next-generation lithium metal batteries.

Nanoalloy electrocatalysis: simulating cyclic voltammetry from configurational thermodynamics with adsorbates

Simulated 2-dimensional cyclic voltammetry for nanoalloys with a hybrid ensemble scheme in Monte Carlo simulation based on the cluster expansion method.

Configurational thermodynamics of alloyed nanoparticles with adsorbates

Changes in the chemical configuration of alloyed nanoparticle (NP) catalysts induced by adsorbates under working conditions, such as reversal in core-shell preference, are crucial to understand and design NP functionality. We extend the cluster expansion method to predict the configurational thermodynamics of alloyed NPs with adsorbates based on density functional theory data. Exemplified with PdRh NPs having O-coverage up to a monolayer, we fully detail the core-shell behavior across the entire range of NP composition and O-coverage with quantitative agreement to in situ experimental data. Optimally fitted cluster interactions in the heterogeneous system are the key to enable quantitative Monte Carlo simulations and design.

Effect of particle size on hydrogen release from sodium alanate nanoparticles

Density functional theory and the cluster expansion method are used to model 2-10 nm sodium alanate (NaAlH(4)) nanoparticles and related decomposition products Na(3)AlH(6), NaH, and Al. While bulk sodium alanate releases hydrogen in a two-step process, our calculations predict that below a certain size sodium alanate nanoparticles decompose in a single step directly to NaH, Al, and H(2) due to the effect of particle size on decomposition thermodynamics. This may explain why sodium alanate nanoparticles, unlike bulk sodium alanate, have been observed to release hydrogen in the operating temperature range of proton exchange membrane fuel cells. In addition, we identify low-energy surfaces that may be important for the dynamics of hydrogen storage and release from sodium alanate nanoparticles.

Phase relationships and structures of inorganic crystals by a combination of the cluster expansion method and first principles calculations

Properties of crystalline solutions are generally dependent not only on their chemical composition but also on the configurations of solute atoms and/or point defects. Quantitative knowledge of the configuration-dependent properties is therefore essential for materials design. The cluster expansion (CE) method has been widely used to describe the configurational properties. Increases in computational power and advances in numerical techniques enable us to perform a large set of systematic first principles calculations based on density functional theory (DFT) to be combined with CE calculations. In this paper, our procedure of CE with optimal selections of clusters and DFT structures is described. Two examples of such calculations are then shown. One is the cation arrangement in a series of spinel oxides. The other is arrangement of the oxygen vacancy in a series of tin sub-dioxides.

Cluster expansion of electronic excitations: Application to fcc Ni–Al alloys

The cluster expansion method is applied to electronic excitations and a set of effective cluster densities of states (ECDOS) is defined, analogous to effective cluster interactions (ECIs). The ECDOSs are used to generate alloy thermodynamic properties as well as the equation of state (EOS) of electronic excitations for the fcc Ni-Al systems. When parent clusters have a small size, the convergence of the expansion is not so good but the electronic density of state (DOS) is well reproduced. However, the integrals of the DOS such as the cluster expanded free energy, entropy, and internal energy associated with electronic excitations are well described at the level of the tetrahedron-octahedron cluster approximation, indicating that the ECDOS is applicable to produce electronic ECIs for cluster variation method (CVM) or Monte Carlo calculations. On the other hand, the Gruneisen parameter, calculated with first-principles methods, is no longer a constant and implies that the whole DOS profile should be considered for EOS of electronic excitations, where ECDOS adapts very well for disordered alloys and solid solutions.

First principles calculation of the interdiffusion coefficient in binary alloys

The atomic mechanisms of diffusion in alloys are complex due to the variations of migration energies with environment and the correlations induced by short-range order between the different components. We present a first-principles approach for calculating vacancy-mediated diffusion coefficients in crystalline binary alloys and apply it to obtain the interdiffusion coefficient of Al(1-x)Lix. The rigorous treatment of atomic migration indicates that short- and long-range order induces strongly correlated migration mechanisms that deviate from random walk behavior.

Reliable first-principles alloy thermodynamics via truncated cluster expansions

In alloys cluster expansions (CE) are increasingly used to combine first-principles electronic-structure calculations and Monte Carlo methods to predict thermodynamic properties. As a basis-set expansion in terms of lattice geometrical clusters and effective cluster interactions, the CE is exact if infinite, but is tractable only if truncated. Yet until now a truncation procedure was not well defined and did not guarantee a reliable truncated CE. We present an optimal truncation procedure for CE basis sets that provides reliable thermodynamics. We then exemplify its importance in Ni3V, where the CE has failed unpredictably, and now show agreement to a range of measured values, predict new low-energy structures, and explain the cause of previous failures.