Speaker
Description
A common strategy for increasing the ionic conductivity of solid electrolytes is aliovalent doping to
form charge-compensating mobile native defects. For the antiperovskite lithium-ion solid electrolyte
Li3OCl, both supervalent (donor) and subvalent (acceptor) doping schemes have been proposed as
routes to increase numbers of mobile lithium vacancies and lithium interstitials, respectively. These
doping schemes rely on two assumptions: first, that aliovalent doping preferentially promotes the
formation of lithium-defects over competing native defects; and second, that additional mobile
lithium defects can be formed in sufficiently high concentrations to meaningfully enhance the ionic
conductivity. To assess the scope for enhancing mobile defect concentrations, and hence ionic
conductivities, through aliovalent doping in Li3OCl, we have performed a hybrid density-functional
theory study of the defect chemistry and subvalent/supervalent-doping response of this material.
We find that under typical synthesis conditions the dominant native defects are $V_\mathrm{Li}$, $\mathrm{O}_\mathrm{Cl}$, and
$V_\mathrm{Cl}$. Supervalent (acceptor) doping increases the concentrations of both $V_\mathrm{Li}$ and $\mathrm{O}_\mathrm{Cl}$, with the
preferentially-formed defect species dependent on the thermodynamic conditions; chemical potential
regimes in which $\mathrm{O}_\mathrm{Cl}$ is favoured over $V_\mathrm{Li}$ show reduced ionic conductivity on doping. Subvalent
(donor) doping promotes the formation of $V_\mathrm{Cl}$ ahead of $\mathrm{Li}_i$, and results in a nonmonotonic increase
in lithium conductivity owing to the reduction in lithium vacancy concentration. This contrast
with the predictions of simple defect-pair charge-compensation models highlights the importance
of considering a full self-consistent thermodynamic model of native defect species when considering
the effects of aliovalent doping in solid electrolytes.
| Speaker Country | UK |
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