Diffusion of Lithium Ions in Lithium-Argyrodite Solid-State Electrolytes from Equilibrium and Nonequilibrium Molecular Dynamics Simulations

The use of solid-state electrolytes to provide safer, next-generation rechargeable batteries is becoming more feasible as new materials with greater stability and higher ionic diffusion coefficients are designed. However, accurate determination of diffusion coefficients in solids is problematic and reliable calculations are highly sought-after. In this paper we compare diffusion coefficients calculated using nonequilibrium and equilibrium ab initio molecular dynamics simulations for highly diffusive solid-state electrolytes for the first time, to demonstrate the accuracy that can be obtained. Moreover, we show that ab initio nonequilibrium molecular dynamics can be used to determine diffusion coefficients when the diffusion is too slow for it to be feasible to obtain them using ab initio equilibrium simulations. Thereby, using ab initio nonequilibrium molecular dynamics simulations we are able to obtain accurate estimates of the diffusion coefficients of Li ions in Li$_6$PS$_5$Cl and Li$_5$PS$_4$Cl$_2$, two promising electrolytes for all-solid-state batteries. Furthermore, these calculations show that the diffusion coefficient of lithium ions in Li$_5$PS$_4$Cl$_2$ is higher than many other potential all-solid-state electrolytes, making it promising for future technologies. The reasons for variation in conductivities determined using computational and experimental methods are also discussed. It is demonstrated that small degrees of disorder and vacancies can result in orders of magnitude differences in diffusivities of Li ions in Li$_6$PS$_5$Cl, and these factors are likely to contribute to inconsistencies observed in experimentally reported values. Notably, the introduction of Li-vacancies and disorder can enhance the ionic conductivity of Li$_6$PS$_5$Cl.Comment: 32 pages, 8 figures, 2 table

High efficient perovskite solar cells base on niobium doped TiO2 as a buffer layer

Here, the effect of lightly Niobium doped TiO layer on the performance of perovskite solar cells has been studied by using solar cell capacitance simulator (SCAPS). N addition, the effects of Niobium concentration, buffer film thickness and operating temperature on the performance of the perovskite solar cell are investigated. For doping level of 3.0 mol% into the TiO layer, cell efficiency of 18.26% with V of 0.96 V, Jsc of 22.45 mA/ cm and FF of 84.25% has been achieved. Calculations show that thickness widening of Nb-doped TiO layer would decrease the efficiency and Voc of the cells. Increase in operating temperature from 300 k to 400 k would weaken the performance of the perovskite solar cell with both pure and Nb-doped TiO layers. However, the cell with Nb-doped TiO layer shows higher stability than the cell with pure TiO buffer at higher temperatures

Colour Diffusion implementation in CP2K

Source code and an example for non-equilibrium molecular dynamics with CP2K, instructions for compiling the cod

The role of ion migration, octahedral tilt, and the A-site cation on the instability of Cs1-xFAxPbI3

Abstract Organic-inorganic hybrid perovskites are promising materials for the next generation photovoltaics and optoelectronics; however, their practical application has been hindered by poor structural stability mainly caused by ion migration and external stimuli. Understanding the mechanism(s) of ion migration and structure decomposition is thus critical. Here we observe the sequence of structural changes at the atomic level that precede structural decomposition in the technologically important Cs1-xFAxPbI3 using ultralow dose transmission electron microscopy. We find that these changes differ, depending upon the A-site composition. Initially, there is a random loss of FA+, complemented by the loss of I-. The remaining FA+ and I- ions then migrate, unit cell by unit cell, into an ordered and more stable phase with a √2 x √2 superstructure. Further ion loss is accompanied by A-site dependent octahedral tilt modes and associated tetragonal phases with different stabilities. These observations of the loss of FA+/I- ion pairs, ion migration, octahedral tilt modes, and the role of the A-cation, provide insights into the atomic-scale structural mechanisms that drive and block ion loss and ion migration, opening pathways to inhibit ion loss, migration and improve structural stability

Enhanced Hydrogen Evolution Performance of Carbon Nitride Using Transition Metal and Boron Co‐Dopants

Density functional theory calculations are used to study the effect of several metal dopants (M = Ag, Cd, Co, Cu, Fe, Ni, Pt, Sc, Ti, and Zn) and metal–boron co‐dopants on the structure and catalytic property of g‐C3N4 2D monolayer. Using transition metals and boron (TM–B) as co‐dopants not only keeps the 2D structure stability of g‐C3N4 monolayer, but also alters the catalytic performance of the structures. The co‐doping of B in TM (TM = Pt, Zn, Cd, Ti, and Sc)‐doped g‐C3N4 leads to a significant increase in the hydrogen adsorption energy because hydrogen binding site changes from N to C. For TM–B (TM = Fe, Co, and Ni) co‐doped g‐C3N4, the hydrogen adsorption energy has no obvious change since the hydrogen binding site remains on C atom near the doped TM. However, the co‐doping of B in TM‐ (TM = Cu and Ag) doped g‐C3N4 leads to a significant reduction of hydrogen adsorption energy, making them good candidates for hydrogen evolution reaction. This study provides theoretical guidance for the experimental synthesis of TM–B co‐doped g‐C3N4 and paves a way for the design of a widely applicable non‐noble catalyst