Combined Experimental and Computational Study of Ce-Doped La₃Zr₂Li₇O₁₂ Garnet Solid-State Electrolyte

Abstract

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.

X-ray pair distribution function analysis and electrical and electrochemical properties of cerium doped Li5La3Nb2O12 garnet solid-state electrolyte

“…S3 †), which is consistent with our previous work on Ce doped Li 7 La 3 Zr 2 O 12 , and represents a reduced interfacial resistance attributed to the formation of a mixed valence Ce 4+ /Ce 3+ product at the electrode/lithium interface. 48 Long-term cycling properties of the Li//Li 5.75 La 3 Nb 1.25 Ce 0.75 O 12 //Li cell at 55°C are shown in Fig. 9b.…”

“…46,47 In contrast, we showed in a previous study, that there was a greater degree of Ce 4+ substitution possible on the Zr 4+ site in Li 7 La 3 Zr 2 O 12 leading to a reduction in the tetragonal distortion, which consequently increased the ionic conductivity, although due to the stoichiometric Li content in this system, the room temperature conductivity was just below the value of 10 −4 S cm −1 , which is considered the minimum for applications. 48 In this paper, the possibility to replace Ce 4+ on the Nb 5+ site in Li 5 La 3 Nb 2 O 12 with the creation of excess Li + as the charge compensation mechanism has been examined for the first time, aiming to enhance the overall conductivity for these Ce doped garnets, in addition to providing the beneficial decrease in the interfacial impedance previously reported for Ce-doped Li with x = 0, 0.25, 0.5, 0.75 and 1 were prepared from intimately ground stoichiometric amounts of starting reagents which were heated initially to 650°C for 12 hours at a rate of 5°C min −1 . 10-15% excess Li 2 CO 3 was then added to the precursor and the powder milled for 30 minutes using a Pulverisette 5 planetary ball mill.…”

Low temperature synthesis of garnet solid state electrolytes: Implications on aluminium incorporation in Li7La3Zr2O12

“…An insulating Li 2 CO 3 layer usually forms in humid atmosphere due to H + /Li + exchange, which is demonstrated to be effectively removed through mechanical polishing inside a glove box 42 . Both metal or non-metal coating and consequently alloying with Li metal, and polymer -garnet composite systems have been applied to try to decrease the high interfacial resistance and limit dendrite growth through the garnet electrolyte [43][44][45][46][47][48][49][50] .…”

Evaluation of the effect of site substitution of Pr doping in the lithium garnet system Li5La3Nb2O12

“…This stoichiometric system is tetragonal at room temperature, with comparatively low conductivity, and changes to a cubic cell at around 750°C; this temperature can be reduced to 350°C by doping at the Zr site with Ce, leading to an increase in conductivity. 24 Stabilisation of the cubic cell at room temperature (c-LLZO) requires a reduction of the lithium content, often using Al or Ga substitution at the Li site. 16,25,26 Dopants at the Zr site (e.g.…”