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

Abstract

Aliovalent doping of solid electrolytes with the intention of increase the concentration of chargecarrying mobile defects is a common strategy for enhancing their ionic conductivities. For the antiperovskite lithium-ion solid electrolyte Li 3 OCl, both supervalent (donor) and subvalent (acceptor) doping schemes have previously been proposed. The effectiveness of these doping schemes depends on two conditions: first, that aliovalent doping promotes the formation of mobile lithium vacancies or interstitials rather than competing immobile defects; and second, that any increase in lithium defect concentration gives a corresponding increase in ionic conductivity. To evaluate the effectiveness of aliovalent doping in Li 3 OCl, we have performed a hybrid density-functional theory study of the defect chemistry of Li 3 OCl and the response to supervalent and subvalent doping. In nominally stoichiometric Li 3 OCl the dominant native defects are predicted to be VLi, O Cl , and V Cl . Supervalent doping increases VLi and O Cl concentrations, with the preferentially-formed defect species dependent on synthesis conditions. Subvalent doping increases the concentration of V Cl more than the concentration of Lii under all accessible synthesis conditions. While supervalent doping is predicted to be effective at increasing ionic conductivity, particularly under Li-poor synthesis conditions, subvalent doping is predicted to decrease room-temperature ionic conductivities at low-to-moderate doping levels. This effect is due to a reduction in the number of lithium vacancies formed during synthesis, and increased V Li + Li i Frenkel-pair recombination upon cooling to room temperature. The strongly asymmetric doping response of Li 3 OCl with respect to supervalent versus subvalent doping is explained as a consequence of the low [VLi + V Cl ] Schottky pair formation energy, suggesting analogous behaviour should be expected in other Schottky-disordered solid electrolytes.

Cation disorder dominates the defect chemistry of high-voltage LiMn1.5Ni0.5O4 (LMNO) spinel cathodes

“…the reverse reaction of Frenkel pair formation) at lower temperatures. 122,123 Two variations of the "frozen" approach were applied. The former approach only allowed V Li and Li i concentrations to vary, whereas the latter also allowed Li Mn and Li Ni concentrations to change.…”

Fabrication of thin solid electrolytes containing a small volume of an Li3OCl-type antiperovskite phase by RF magnetron sputtering

“…43,44 Indeed, several computational studies have examined the roles of crystallographic defects -in particular Li + vacancies and interstitials -in facilitating Li + conduction in Li 3 OCl. 15,[21][22][23][24][45][46][47][48][49][50] These defects can be created by adjusting the ratio of Li 2 O and LiCl precursors used in synthesis or by adding aliovalent dopant ions such as Mg 2+ . A band gap of 3.7-4.4 eV 44 has been predicted for grain boundaries in Li 3 OCl compared to the 1-3 eV band gap measured for 50% of grain boundaries in Li 7 La 3 Zr 2 O 12 ; 51 in both cases the grain boundary band gap is thought to be smaller than that of the bulk material, limiting the electrochemical stability of polycrystalline samples.…”