First-principles density functional calculations were used to calculate surface properties of the LiMn 2 O 4 spinel. The calculations were benchmarked to obtain the correct semiconducting, JahnTeller distorted electronic ground state of bulk LiMn 2 O 4 and, using the same parameters, the predominant low-index polar surface facets (100), (110), and (111) were calculated to study their structure and stability. Following an investigation of possible surface terminations as well as surface layer reconstructions we find that the (111) LMO surface stabilizes through a targeted site-exchange of the under-coordinated surface Mn cations with fully coordinated tetrahedral sub-surface Li cations, effectively creating a partial inverse spinel arrangement at the surface.This reconstruction renders the (111) facet the most stable among the investigated facets. The equilibrium (Wulff) shape of a LiMn 2 O 4 particle was constructed and exhibits a cubo-octahedral shape with predominant (1 1 1) facets, in agreement with common experimental findings for the spinel structure.

Soft X‐ray absorption spectroscopy with different probe depth was employed to characterize the solid electrolyte interphases (SEIs) formed on β‐Sn single crystals with two different surface orientations. Based on comparative studies of C‐K, O‐K, and F‐K absorption spectra between the SEIs and reference samples, SEI on Sn (100) mainly consists of porous Li2CO3 species with electrolyte uptake, while SEI on Sn (001) essentially consists of LiF and organic molecules, with a small amount of –CO3 and electrolyte buried inside. Theoretical calculation suggests that Sn (001) surface is more reactive than (100), especially after air exposure. The reactive (001) surface facilitates the decomposition of LiPF6 to form a LiF layer. In contrast, SEI on (100) surface is predominately from the typical decomposition of carbonate‐based electrolyte. While the LiF passivates Sn (001) electrode after one cycle, the porous carbonate layer on (100) surface does not prevent further decomposition of electrolyte after many cycles. This leads to drastically different electrochemical behavior and morphology of the two SEIs. The result is a direct proof that surface properties of active materials could strongly impact the SEI formation on electrodes even with the same electrolyte. Such effect could lead to distinct SEI formation and electrochemical performance.

We present a novel way of performing kinetic Monte Carlo simulations which does not require an a priori list of diffusion processes and their associated energetics and reaction rates. Rather, at any time during the simulation, energetics for all possible (single or multi-atom) processes, within a specific interaction range, are either computed accurately using a saddle point search procedure, or retrieved from a database in which previously encountered processes are stored. This self-learning procedure enhances the speed of the simulations along with a substantial gain in reliability because of the inclusion of many-particle processes. Accompanying results from the application of the method to the case of two-dimensional Cu adatom-cluster diffusion and coalescence on Cu (111) with detailed statistics of involved atomistic processes and contributing diffusion coefficients attest to the suitability of the method for the purpose.

Diffusion of small two-dimensional Cu islands ͑containing up to 10 atoms͒ on Cu͑111͒ has been studied using the newly developed self-learning Kinetic Monte Carlo ͑SLKMC͒ method which is based on a database of diffusion processes and their energetics accumulated automatically during the implementation of the SLKMC code. Results obtained from simulations in which atoms hop from one fcc hollow site to another are compared with those obtained from a parallel set of simulations in which the database is supplemented by processes revealed in complementary molecular dynamics simulations at 500 K. They include processes involving the hcp ͑stacking-fault͒ sites, which facilitate concerted motion of the islands ͑simultaneous motion of all atoms in the island͒. A significant difference in the scaling of the effective diffusion barriers with island size is observed in the two cases. In particular, the presence of concerted island motion leads to an almost linear increase in the effective diffusion barrier with size, while its absence accounts for strong size-dependent oscillations and anomalous behavior for trimers and heptamers. We also identify and discuss in detail the key microscopic processes responsible for the diffusion and examine the frequencies of their occurrence, as a function of island size and substrate temperature.