Concentration of Charge Carriers, Migration, and Stability in Li₃OCl Solid Electrolytes

Abstract

Recently, a new family of lithium-rich antiperovskites, Li 3 OA (A = halogen), which presents superionic conductivity, emerged as a promising both safe and commercially applicable solid electrolyte for lithium ion batteries. In this paper we employed classical atomistic quasistatic calculations to obtain the concentration of lithium vacancies and interstitials for stoichiometric samples of Li 3 OCl. The obtained concentrations as well as vacancy and interstitial migration energies reinforced the assumption that vacancies are the charge carriers in both stoichiometric and divalent metal doped samples, but raise the possibility that the high ionic conductivity in LiCl-deficient samples are in fact driven by interstitials, in opposition to what has been assumed so far. The Li 3 OCl stability at higher temperatures was investigated based on Gibbs energies of decomposition from 0 K up to 550 K. They are negative in the whole temperature range, which suggests that there exists a high Gibbs energy barrier between Li 3 OCl and starter materials preventing decomposition.

Elucidating lithium-ion and proton dynamics in anti-perovskite solid electrolytes

“…It is well known that Li vacancies are the dominant charge carriers in the anhydrous Li 3 OCl material. 27,28,38,45 These results reinforce the fact that there is strong correlation between Li-ion transport and proton concentration.…”

“…10), which is indicative of the favourable migration pathways along these pathways, as found previously. 28 In contrast, there are no long-range proton diffusion pathways, with only O-H rotational motion. This is perhaps unsurprising when we consider the O-O distance of 3.91 Å in these materials compared to proton-conducting perovskite 54 Clearly, the large O-O distances in these anti-perovskite systems will inhibit significant proton hopping transport.…”

“…[7][8][9][10][11] Although the high Li-ion conductivities of Li-rich antiperovskite materials have been known for decades, 12,13 it is only recently that significant interest has been generated for solid electrolyte applications. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] Zhao and Daemen 14 reported high ionic conductivities (410 À3 S cm À1 at room temperature) and low activation energies (0.18-0.26 eV) for Li 3 OX-based compositions, where X = Cl or Br. However, subsequent reports have noted reduced Li-ion conductivities and increased activation barriers for these materials.…”

New horizons for inorganic solid state ion conductors

“…However, the high ion conductivity of lithium anti-perovskites could not be explained by this mechanism, because of the high formation energy of Li interstitial defects. 100 Later, Mouta et al 101 employed classical atomistic simulation computations to calculate the concentration of Li vacancies and interstitials in Li 3 OCl. Vacancies created by Schottky defects were predicted to be the charge carriers in Li 3 OCl, since the concentration of interstitials (i.e., Frenkel defects) was 6 orders of magnitude lower due to the very high energy required for their formation.…”

Antiperovskite Li3OCl Superionic Conductor Films for Solid‐State Li‐Ion Batteries

“…), has been developed as a promising solid electrolyte. [15][16][17][18][19][20] This class of electrolytes accommodates a large number of Li ions in the crystal lattice and the Li ions can move easily by introducing certain amounts of crystal defects, such as Li + and Clvacancies. The most important advantages of the LiRAP electrolyte include (1) high ionic conductivity and low energy barrier for Li transport, (2) low electronic conductivity (Li 3 OCl with a band gap exceeding 5 eV [ 16,17 ] ) with minimum self-discharge for long shelf life, (3) wide electrochemical working windows beyond 5 V compatible with high-potential cathodes, (4) stable operation at high temperatures up to 275 °C, and (5) environmental friendliness.…”