Native Defects and Their Doping Response in the Lithium Solid Electrolyte Li₇La₃Zr₂O₁₂

Abstract

The Li-stuffed garnets LixM2M 3 O12 are promising Li-ion solid electrolytes with potential use in solid-state batteries. One strategy for optimising ionic conductivities in these materials is to tune lithium stoichiometries through aliovalent doping, which is often assumed to produce proportionate numbers of charge-compensating Li vacancies. The native defect chemistry of the Li-stuffed garnets, and their response to doping, however, are not well understood, and it is unknown to what degree a simple vacancy-compensation model is valid. Here, we report hybrid density-functional-theory calculations of a broad range of native defects in the prototypical Li-garnet Li7La3Zr2O12. We calculate equilibrium defect concentrations as a function of synthesis conditions, and model the response of these defect populations to extrinsic doping. We predict a rich defect chemistry that includes Li and O vacancies and interstitials, and significant numbers of cation-antisite defects. Under reducing conditions, O vacancies act as colour-centres by trapping electrons. We find that supervalent (donor) doping does not produce charge compensating Li vacancies under all synthesis conditions; under Li-rich / Zr-poor conditions the dominant compensating defects are LiZr antisites, and Li stoichiometries strongly deviate from those predicted by simple "vacancy compensation" models.

The Devil is in the Defects: Electronic Conductivity in Solid Electrolytes

“…Previous investigations of native defects in SEs have put emphasis on strategies to improve ionic conductivity. [54][55][56]68,69 In this study, we focus on all native defects that may alter the concentration of charge carriers (electrons, holes), in addition to ionic carriers i.e., Li + and Na + ions. In a previous study, 55 we found V Na +Li +…”

Electrochemical Impedance Spectroscopy for All‐Solid‐State Batteries: Theory, Methods and Future Outlook

“…[116] Such aliovalent doping strategies are common in inorganic SEs to introduce and charge-balance bulk defects favourable to ionic conduction, e. g. Li vacancies or interstitials. [117,118] Traditionally, EIS studies relevant to oxide SEs focused on new synthesis routes or to methods to increase the ionic conductivity, however recent work has investigated its fascinating interfacial properties with Li and several oxide-based devices have been reported.…”

Mechanistic Origin of Superionic Lithium Diffusion in Anion-Disordered Li6PS5X Argyrodites

“…The set of lithium ions that define a specific coordination polyhedron (all those within r coord of the central atom) can be described by a vertex list of these ion indices, e.g. (1,3,7,20,52,100). The edge topology connecting these ions is described by an undirected edge graph, where we consider an edge formed between any two vertices of a polyhedron with a separation smaller than a threshold distance r edge .…”

“…Although a number of highly conducting solid lithiumion electrolytes are known, none meet all the criteria for general commercial use [1,[4][5][6]. Identifying new solid lithium-ion electrolytes is an active area of research [3], with strategies ranging from targeted chemical modification of known solid electrolytes, to improve their conductivities [7][8][9][10][11], to high-throughput screening of new materials [12][13][14][15]. In both cases, it is useful to understand why some materials are highly-conducting, yet others are not * b.j.morgan@bath.ac.uk [3,[16][17][18][19][20].…”