Modeling of Magnesium Intercalation into Chevrel Phase Mo₆S₈: Report on Improved Cell Design

Abstract

A good understanding of the limiting processes in rechargeable magnesium batteries is key to develop novel high-capacity/ high-voltage cathode materials. Thereby, the performance of magnesium-ion batteries can strongly depend on the morphology of the intercalation cathode. Moreover, high mass loadings are essential for commercialization. In this work the influence of different mass loadings are studied in addition to the impact of the particle size distribution of the active material. Therefore, a detailed continuum model is developed, which is able to describe the complex intercalation of magnesium into a Chevrel phase (CP) cathode. The model considers the thermodynamics, kinetics and interplay of the two energetically different intercalation sites of Mo 6 S 8 , which results from its unique crystal structure, as well as the impact of the desolvation on the electrochemical reactions and possible ion agglomeration. Ideal combinations of mass loading and electrolyte concentration as well as the desired CP particle size are determined for the stateof-the-art magnesium tetrakis(hexafluoroisopropyloxy)borate Mg[B(hfip) 4 ] 2 electrolyte.

Single Crystal Layered Oxide Cathodes: The Relationship between Particle Size, Rate Capability, and Stability

“…[41] For example, should the C-rate be sufficiently high, smaller particles could experience self-accelerated delithiation from increasing lithium diffusivity well before larger particles in the size distribution yet are exposed to coulometric conditions, which drives undesired states of charge and accelerated degradation; [42] however the nature of this phenomenon is subject to active study. [30,43] Wessel van den Bergh is a post-doctoral researcher at the Battery and Electrochemistry Laboratory (BELLA) at the Karlsruhe Institute of Technology (KIT). His research interests are focused on the use of controlled design methodologies to study the relationship between material features and electrochemical behavior for energy-storage applications.…”

“…While not an issue that arises from path length, the distribution of path lengths that is experimentally observed to broaden with increased particle size [33,40] can be a cause of issues in relation to autocatalytic delithiation (see Figure 1). [41] For example, should the C‐rate be sufficiently high, smaller particles could experience self‐accelerated delithiation from increasing lithium diffusivity well before larger particles in the size distribution yet are exposed to coulometric conditions, which drives undesired states of charge and accelerated degradation; [42] however the nature of this phenomenon is subject to active study [30,43] …”

Ion Mobility in Crystalline Battery Materials

“…to be limited by the particle size of the Chevrel phase material with particles smaller than ≈0.5 µm being crucial to avoid transport limitations for a wide range of practical current densities. [ 185 ] Another interesting field for the CP is the usage of dual ion systems. This was investigated by Li et al., proving that the diffusion of divalent Mg ions is significantly facilitated by using a Li and Mg dual‐ion system as the activation energy is remarkably reduced specifically by the concerted interactions of preceding Li ions and following Mg ions.…”

“…Usually the efficiency of the solid state system is limited by the reachable capacity, but was found by Drews et al to be limited by the particle size of the Chevrel phase material with particles smaller than ≈0.5 μm being crucial to avoid transport limitations for a wide range of practical current densities. [185] Another interesting field for the CP is the usage of dual ion systems. This was investigated by Li et al, proving that the diffusion of divalent Mg ions is significantly facilitated by using a Li and Mg dual-ion system as the activation Figure 14.…”