Madelung-Buckingham model as applied to the prediction of voltage, crystal volume changes, and ordering phenomena in spinel-type cathodes for lithium batteries

Software for Evaluating Long-Range Electrostatic Interactions Based on the Ewald Summation and Its Application to Electrochemical Energy Storage Materials

Electrochemical characteristics such as open-circuit voltage and ionic conductivity of electrochemical energy storage materials are easily affected, typically negatively, by mobile ion/vacancy ordering. Ordered phases can be identified based on the lattice gas model and electrostatic energy screening. However, the evaluation of long-range electrostatic energy is not straightforward because of the conditional convergence. The Ewald method decomposes the electrostatic energy into a real space part and a reciprocal space part, achieving a fast convergence in each. Due to its high computational efficiency, Ewald-based techniques are widely used in analyzing characteristics of electrochemical energy storage materials. In this work, we present software not only integrating Ewald techniques for two-dimensional and three-dimensional periodic systems but also combining the Ewald method with the lattice matching algorithm and bond valence. It is aimed to become a useful tool for screening stable structures and interfaces and identifying the ionic transport channels of cation conductors.

Space-Charge Layers in All-Solid-State Batteries; Important or Negligible?

All-solid state batteries have the promise to increase the safety of Li-ion batteries. A prerequisite for high-performance all-solid-state batteries is a high Li-ion conductivity through the solid electrolyte. In recent decades, several solid electrolytes have been developed which have an ionic conductivity comparable to that of common liquid electrolytes. However, fast charging and discharging of all-solid-state batteries remains challenging. This is generally attributed to poor kinetics over the electrode-solid electrolyte interface because of poorly conducting decomposition products, small contact areas, or space-charge layers. To understand and quantify the role of space-charge layers in all-solid-state batteries a simple model is presented which allows to asses the interface capacitance and resistance caused by the space-charge layer. The model is applied to LCO (LiCoO₂) and graphite electrodes in contact with an LLZO (Li₇La₃Zr₂O₁₂) and LATP (Li_1.2Al_0.2Ti_1.8(PO₄)₃) solid electrolyte at several voltages. The predictions demonstrate that the space-charge layer for typical electrode-electrolyte combinations is about a nanometer in thickness, and the consequential resistance for Li-ion transport through the space-charge layer is negligible, except when layers completely depleted of Li-ions are formed in the solid electrolyte. This suggests that space-charge layers have a negligible impact on the performance of all-solid-state batteries.