Computational Predictions of the Stability of Fluorinated Calcium Aluminate and Borate Salts

Abstract

Energy storage concepts based on multivalent ions, such as calcium, have great potential to become next-generation batteries due to their low cost and comparable cell voltage and energy density to Li-ion batteries. However, the development of Ca batteries is still hindered by the lack of suitable materials that grant a long cycle life. Specific to electrolyte materials, developing a calcium salt that is chemically stable under ambient conditions and enables reversible electrodeposition of Ca is critical. In this work, we use first-principles calculations to study the intrinsic and reductive stability of twelve Ca salts with fluorinated aluminate and borate anions and analyze the decomposition products formed on the metal anode surface that are critical to early-stage solid electrolyte interphase formation. We found anions with significant steric hindrance and a high degree of fluorination are intrinsically less stable and deemed unviable designs for Ca salt. Aluminate salts are generally less reactive with the Ca anode than their borate counterparts, and a high degree of fluorination leads to weaker reductive stability. Calcium fluoride is the most prominent decomposition product on the anode surface, and carbide-like motifs were also found from the decomposition of the designed salts.

Design Principles and Routes for Calcium Alkoxyaluminate Electrolytes

“…Previously, a few alkoxyaluminates were identified as reductive stable through computational analysis of the transition states along the decomposition pathways . Among the Ca–Al compounds, a range of ligands were predicted to exhibit higher than 0.6 eV decomposition barriers, and Ca­[Al­(tftb) 4 ] 2 in particular exhibited a 1.0 eV kinetic barrier toward reductive decomposition.…”

“…Alkoxyaluminates and alkoxyborates are two groups of WCAs that have found success in recent metal anode investigations due to their excellent reductive and oxidative stability and resulting high Coulombic efficiency. ,,, These alkoxyaluminate and alkoxyborate structures can be designed in multiple ways by substituting alkoxide ligands to target optimal electrolyte characteristics. Two recent computational studies explored the stability of alkoxyaluminate and alkoxyborate salts incorporating a range of alkoxides and their resulting decomposition through density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations . These data indicate a few target structures that are less likely to decompose.…”

A novel calcium fluorinated alkoxyaluminate salt as a next step towards Ca metal anode rechargeable batteries

“…Due to the chemical similarity between B and Al, alkoxyaluminate-based electrolytes for Ca batteries have been investigated by computational studies and were recognized as potential candidates. 20,21 Recently, Leon et al reported calcium tetrakis(perfluoro- tert -butoxy) aluminate salt, which has displayed inferior Ca plating/stripping performance to the state-of-the-art CaBhfip electrolyte. 22 Nonetheless, a higher thermodynamic stability of the [Al(hfip) 4 ] − anion, as well as superior performance of Mg[Al(hfip) 4 ] 2 salt over its boron analogue motivated us to develop a synthesis procedure for the preparation of Ca[Al(hfip) 4 ] 2 salt (hereinafter denoted as CaAlhfip).…”

Two Layers of Computational Screening on Silaborane‐based Clusters Filter Ca(SiB11H11CH3)2 as the Promising Electrolyte for Calcium‐Ion Batteries

“…Investigating the interaction of electrolyte with the metal anodes is a promising approach to predict their stability/ decomposition, possible decomposition pathways and products comprising the passivation layer and so on. [48][49][50][51][52][53] Hence, ab initio molecular dynamics simulations of the electrolytes based on calcium salts of silaboranes over the Ca anode surface were carried out to explore the real-time behaviour of the electrolytes. The charge transfer from the Ca anode surface to electrolytes was probed to gain insights into the interactions between the salts and the anode with time and the decomposition of salts over the anode.…”

“…Investigating the interaction of electrolyte with the metal anodes is a promising approach to predict their stability/decomposition, possible decomposition pathways and products comprising the passivation layer and so on [48–53] . Hence, ab initio molecular dynamics simulations of the electrolytes based on calcium salts of silaboranes over the Ca anode surface were carried out to explore the real‐time behaviour of the electrolytes.…”