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 charge carrying mobile defects is a common strategy for enhancing their ionic conductivities. For the antiperovskite lithium-ion solid electrolyte Li3OCl, 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 Li3OCl, we have performed a hybrid density-functional theory study of the defect chemistry of Li3OCl and the response to supervalent and subvalent doping. In nominally stoichiometric Li3OCl the dominant native defects are predicted to be VLi, OCl, and VCl. Supervalent doping increases VLi and OCl concentrations, with the preferentially formed defect species dependent on synthesis conditions. Subvalent doping increases the concentration of VCl 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 [VLi + Lii] Frenkel-pair recombination upon cooling to room temperature. The strongly asymmetric doping response of Li3OCl with respect to supervalent versus subvalent doping is explained as a consequence of the low [VLi + VCl] Schottky pair formation energy, suggesting analogous behaviour should be expected in other Schottky-disordered solid electrolytes.

Defect chemistry and ion transport in low-dimensional-networked Li-rich anti-perovskites as solid electrolytes for solid-state batteries

“…This result suggests that Li 6 OCl 4 may present interstitial diffusion as the main ion transport mechanism and not a Li vacancy hopping mechanism, in contrast to the other anti-perovskites investigated, as well as to what has been predicted for this structure in the literature previously. 57 Frenkel-type defects have been reported to be more mobile in anti-perovskites and other important solid electrolytes and present lower migration barriers than other types of defects, 43,44,55,74 which could potentially lead to more favourable ion transport mechanisms in systems possessing higher concentrations of Frenkel-type defects. Therefore, these results indicate that Li-ion transport and conductivity could be enhanced in Li 6 OCl 4 compared to the other investigated systems, as also discussed below.…”

Editors’ Choice—Review—Designing Defects and Diffusion through Substitutions in Metal Halide Solid Electrolytes

“…Defect diagrams have historically been calculated to identify defects and compensation mechanisms for doping in semiconductors, and have recently been applied to substitutions in solid electrolytes. 85,[87][88][89][90] In future studies, leveraging these computational methods could guide experimental studies and enable rational design of substituted ternary metal halides. • While some members of the A 3 MX 6 family are reported to be relatively tolerant to ambient humidity, 6 the impact of substituting ions on the environmental stability of these materials has not yet been explored in depth.…”

Exploiting Nanoscale Complexion in LATP Solid-State Electrolyte via Interfacial Mg2+ Doping

“…With a formal charge of = +2, which is different from all other cations in LATP, Mg allows for aliovalent substitution. From an engineering perspective, this is often exploited in highly ordered materials in order to introduce defined cationic defects which may enhance ion mobility [ 49 ]. In amorphous phases, aliovalent doping opens a design route to deliberately alter the cationic composition by e.g., decreasing the fraction of higher valent cations while increasing lower valent ones.…”