We first consider the formation energies and equilibrium concentrations of native defects in undoped, nominally stoichiometric, Li 3 OCl. Figure shows formation energies of native defects in Li 3 OCl as a function of Fermi energy, under Li-poor and Li-rich conditions (upper panels), and the corresponding equilibrium defect concentrations (lower panels). Under Li-poor conditions, the dominant defect species are lithium vacancies, V Li , and chlorine vacancies, V Cl , which is qualitatively consistent with previous predictions of Li 3 OCl as being predominantly [V Li + V Cl ] Schottky-disordered . The dominant [V Li + V Cl ] Schottky disorder can also be assigned directly from the defect formation energies plot (fig. ), which shows the equilibrium Fermi energy is "pinned" by the V Li -V Cl defect pair. Under Li-rich conditions, chlorine vacancies, V Cl , are the dominant positively charged defect species. The dominant negatively charged defect, however, is now the oxygen-chlorine antisite, O Cl . From a charge-and mass-balanced defect antisite pairs have been predicted via ab initio molecular dynamics to enhance lithium diffusion relative to a perfectly anion-ordered reference system . Anion framework disorder has also been associated with increased ionic conductivity in other antiperovskites and in other lithium-ion solid electrolytes . Synthesis protocols that increase the degree of host-frameworkdisorder in Li 3 OCl, or in other antiperovskites, may therefore provide alternative routes to improving the ionic conductivities of these materials beyond purely modifying lithium stoichiometry.