Atomistic Insights into the Effects of Doping and Vacancy Clustering on Li-Ion Conduction in the Li₃OCl Antiperovskite Solid Electrolyte

Abstract

Solid-state batteries are currently attracting increased attention because of their potential for significant improvements in energy density and safety as compared to liquid electrolyte-based batteries. Lithium-rich antiperovskites, such as Li 3 OCl, are of particular interest, but the effects of doping on lithium mobility are not fully understood at the atomic level. Here, we investigate the impact of divalent cation (Mg 2+ , Ca 2+ , Sr 2+ , and Ba 2+ ) and F − doping on the ion conduction properties of Li 3 OCl, using both defect simulation and molecular dynamics techniques. Our results show that the F-doped system has a low conductivity and high activation barriers. This is attributable to high binding energies, which leads to the formation of stable dopant−vacancy pairs, preventing long-range lithium-ion mobility. In contrast to the F-doped system, Mg dopants (shown to be the most favorable dopant on the Li + site) have lower binding energies to lithium vacancies, yielding higher lithium-ion conductivities and lower migration energies. Our results indicate a viable doping strategy to improve the electrochemical performance of antiperovskite solid electrolytes.

Atomic-scale investigation of cation doping and defect clustering in the anti-perovskite Na3OCl sodium-ion conductor

“…The starting point of the modelling study was to reproduce the experimentally observed crystal structure using potentials-based techniques (see Methods section for details), which have been applied successfully to a rich variety of battery electrode and solid electrolyte materials. 22,30,52 The anti-perovskite crystal structure of Na 3 OCl (shown in Fig. 1) consists of oxide ions at the typical B-site of an ABX 3 perovskite, coordinated to six Na + ions at the X-site, and the large Cl − ion occupying the 12-coordinate A-site.…”

“…Atomistic simulation methods have been applied to a wide range of solid-state compounds including Li- and Na-ion battery materials. 22,52,57–59 However, there are only a few examples of these strategies being applied to Na-rich anti-perovskites. 30,35 The use of such atomistic simulations can provide valuable insight into ion diffusion over longer timescales and greater lattice sizes than ab initio methods.…”

“…Conductivities are then calculated from these diffusion coefficients via the Nernst–Einstein equation for solid-state diffusion 66 with a Haven ratio of 1, as in previous studies. 22,30 Activation energies are derived using the slopes of the linear fitting of Arrhenius conductivity plots.…”

“…In addition to recent work on Li-rich anti-perovskites Li 3 OX (X = Cl or Br), 19–23 there have been structural and conductivity studies of the sodium analogues Na 3 OX (X = Cl or Br), 24–35 as well as work on a range of other Na-rich anti-perovskites such as Na 3 ONO 2 and Na 3 OBH 4 . 36–51 In comparison to lithium, Na-ion batteries have the advantages of raw material abundance and reduced cost with possible use in large-scale grid storage applications.…”

Aliovalent doping response and impact on ionic conductivity in the antiperovskite solid electrolyte Li3OCl

“…In reality, direct dopant-defect interactions may be significant [7,14,15,91]. For example, supervalent dopants, such as Mg 2+ , are predicted to kinetically trap lithium vacancies [15], which will reduce ionic conductivities relative to the values presented in this work. Despite this limitation, we expect our results to accurately describe quantitative trends for different synthesis conditions and doping strategies for Li 3 OCl.…”