Li-containing garnet materials have been attracting considerable interest as potential solid-state electrolytes for Li ion batteries. In such Ln3M2Li x O12 (Ln = lanthanide, alkaline earth; M = Zr, Hf, Sn, Nb, Ta, Sb, Bi, Te), the best Li ion conductivity is observed for Li contents, x, just below the maximum 7.0. The decrease in conductivity for x = 7.0 systems is related to Li ordering (cell changes from cubic to tetragonal) to prevent too short Li–Li interactions. In this work, we report a combined experimental and modeling study of Ce4+ doping in La3Zr2Li7O12. We show for the first time that Ce4+ can be doped onto the Zr4+ site in this material. This doping strategy results in a reduction in the tetragonal distortion as well as a lowering of the temperature of the tetragonal–cubic phase transition, attributed to the increase in cell size reducing Li–Li interaction strain. Coupled with these changes, the conductivity shows a significant (1.5 orders of magnitude) improvement. Furthermore, the Ce doping also reduces the interfacial resistance (388 Ω cm2 for Li7La3Z1.75Ce0.25O12) in contact with Li metal, giving additional potential benefits to this doping strategy. The long-term cycling stability of a Li//garnet//Li symmetric cell over 190 h has been demonstrated.

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No abstract

Solid-state batteries are a proposed route to safely achieving high energy densities, yet this architecture faces challenges arising from interfacial issues between the electrode and solid electrolyte. Here we develop a novel family of double perovskites, Li1.5La1.5MO6 (M = W6+, Te6+), where an uncommon lithium-ion distribution enables macroscopic ion diffusion and tailored design of the composition allows us to switch functionality to either a negative electrode or a solid electrolyte. Introduction of tungsten allows reversible lithium-ion intercalation below 1 V, enabling application as an anode (initial specific capacity >200 mAh g-1 with remarkably low volume change of ∼0.2%). By contrast, substitution of tungsten with tellurium induces redox stability, directing the functionality of the perovskite towards a solid-state electrolyte with electrochemical stability up to 5 V and a low activation energy barrier (<0.2 eV) for microscopic lithium-ion diffusion. Characterisation across multiple length- and time-scales allows interrogation of the structure-property relationships in these materials and preliminary examination of a solid-state cell employing both compositions suggests lattice-matching avenues show promise for all-solid-state batteries.

The electronic structure properties of four related push–pull systems are studied using time-dependent density functional theory in connection with detailed wavefunction analysis protocols.