Multivalent Ion Transport in Anti-Perovskite Solid Electrolytes

Abstract

Batteries based on the shuttling of multivalent (MV) ions are attractive energy storage systems due to their potential to transfer multiple electrons per working ion. Nevertheless, these batteries remain in an early stage of development, and performance improvements are desired for electrolytes that can transport MV ions efficiently and for cathode materials that can store MV ions at high capacity. The present study explores potential MV solid electrolytes (SEs) based on the anti-perovskite (AP) structure. Ten SE compositions are considered: Mg3NX, Ca3NX (where X = P, As, Sb, or Bi), Ca3PSb, and Ca3AsSb. First-principles calculations are used to predict several properties that are relevant for SE performance: stability, band gaps, elastic moduli, ion migration barriers, and defect formation energies. All compounds are predicted to be thermodynamically stable at 0 K. Similar to the monovalent AP SEs, lattice distortions in the MV systems decrease the energy barrier for percolating ion migration. Large energies associated with the formation of vacancies and interstitials imply that achieving high conductivities will require defect concentrations that are controlled via doping or composition variation. Of the compounds investigated, Mg3NAs, Ca3NAs, and Ca3PSb are the most promising. These SEs are predicted to be stable against Mg or Ca anodes and have barriers for vacancy migration that are less than ∼500 meV (less than ∼200 meV for interstitial migration). Stability against oxidation is maintained up to 1.2–1.7 V, implying that interfacial coatings may be needed to achieve compatibility with high-voltage cathodes.

Multivalent Ion Conduction in Inorganic Solids

“…In lieu of concretely established design principles motivated by experimentally verified structure–property relationships, computational results provide a logical way to filter promising compounds. However, it should be noted that in experimental corroboration of several materials a low NEB-derived E a has not been achieved, ,, highlighting that other factors, such as sufficient carrier concentration or optimization of the precursor (σ 0 ), are likely to be key to observing high RT conductivity. Additionally, future computational investigations should consider the MN energy of the compound to ensure that a low E a is ideal.…”

“…Although MV ions can conduct charge equivalent to monovalent ions with a fraction of the charge carriers, since the successful jump rate of MV ions is lower due to the stronger electrostatic interactions and the higher E m that results, maximizing the number of available sites for MV ions to jump into will be essential for significant long-range conduction. Intrinsic vacancies are formed as Frenkel or Schottky defects, the concentration of which are temperature dependent, and may be too low at ambient temperature to elicit meaningful bulk conduction . Aliovalent substitution is generally used to create a stoichiometric amount of vacancies.…”

Advancing towards a Practical Magnesium Ion Battery

“…The antiperovskite-type structure of Mg 3 NAs has been recently suggested as another class of solid electrolyte, and the theoretical calculations found low migration barrier and stability against Mg [ 133 ]. The same authors pointed out that the stability of Mg 3 NAs would not be enough against a high-voltage cathode.…”

Accelerated Autonomous Workflow For Antiperovskite-based Solid State Electrolytes

“…Li-ion based batteries are not exclusively researched, with SSEs designed for other battery chemistries, such as Na-and Mg-ion batteries, showing similar limitations as for Li-ion batteries. [14,15] Future search of SSEs need to be multi-target inherently such that all required properties are met simultaneously, as materials engineering focused on one property might compromise another, thus failing the overall goal.…”