Synthesis of nano-scale fast ion conducting cubic Li₇La₃Zr₂O₁₂

Abstract

A solution-based process was investigated for synthesizing cubic Li7La3Zr2O12 (LLZO), which is known to exhibit the unprecedented combination of fast ionic conductivity, and stability in air and against Li. Sol-gel chemistry was developed to prepare solid metal-oxide networks consisting of 10 nm cross-links that formed the cubic LLZO phase at 600 ° C. Sol-gel LLZO powders were sintered into 96% dense pellets using an induction hot press that applied pressure while heating. After sintering, the average LLZO grain size was 260 nm, which is 13 times smaller compared to LLZO prepared using a solid-state technique. The total ionic conductivity was 0.4 mS cm(-1) at 298 K, which is the same as solid-state synthesized LLZO. Interestingly, despite the same room temperature conductivity, the sol-gel LLZO total activation energy is 0.41 eV, which 1.6 times higher than that observed in solid-state LLZO (0.26 eV). We believe the nano-scale grain boundaries give rise to unique transport phenomena that are more sensitive to temperature when compared to the conventional solid-state LLZO.

Garnet-Type Li7La3Zr2O12Solid Electrolyte Thin Films Grown by CO2-Laser Assisted CVD for All-Solid-State Batteries

“…Despite the fact that the density cannot be quantified via SEM, a comparison of the cross-section image (Fig. 2a) with SEM images of sintered LLZO pellets with reported densities above 90% [26][27][28][29] confirms the highly dense nature of the LA-CVD grown LLZO film. A film thickness of around 850 nm is estimated from this cross-section for the deposition on Si.…”

“…Especially the overall density is known to play a crucial role for obtaining high conductivities. Considerable effort has been made to achieve higher densities for bulk ceramics using nano-grained LLZO, 26 field assisted sintering technique for compaction, 27,28 or sintering aids like Ga. 29 Therefore, the fact that the performance of the tetragonal LLZO thin film grown by LA-CVD is among the best values reported for tetragonal LLZO so far, is attributed primarily to the high density of the film (see Fig. 2).…”

Electrochemical Stability of Li6.5La3Zr1.5M0.5O12 (M = Nb or Ta) against Metallic Lithium

“…Cubic Al-free LLZTO and LLZNO with the nominal composition Li6.5La3Zr1.5Ta0.5O12 and Li6.5La3Zr1.5Nb0.5O12 were prepared using a sol-gel synthesis method, respectively (Sakamoto et al, 2013). LiNO3⋅x6H2O (x = 0.5, 99.999%, Alfa Aesar), La(NO3)3⋅6H2O (99.9% Sigma Aldrich), Zr(OH7C3) (70 wt.% in 1-propanol, Sigma Aldrich), and Nb(OCH2CH3)5 (99.95%, Sigma Aldrich) and/or Ta(CH3C2H2O)5 (99.98%, Sigma Aldrich) were used as the sol-gel precursors.…”

Preparation of Li7La3(Zr2−,Nb )O12 (x= 0–1.5) and Li3BO3/LiBO2 composites at low temperatures using a sol–gel process

“…The Al doping of LLZO can be favorable to maintain a stable cubic phase at high temperatures. Sakamoto and co-workers [15] reported Li-ion conductivity of 4 × 10 −4 S cm −1 at 25°C for LLZO-Al cubic phase (T s : 1000°C).…”

“…Rangasamy and co-workers have reported that 0.204 mol Al is necessary to stabilize the cubic phase and Li-ion conductivity of 1 × 10 −4 S cm −1 (T s : 1000°C) at 25°C [11]. Actually, the synthesis of LLZO ceramic electrolyte by a sol-gel process has shown the formation of cubic phase at lower calcination temperatures around 700-750°C without addition of Al [12,13] and around 600°C with Al [14,15]. Some materials have shown a transition from cubic to tetragonal phase when the temperature is increased, thereby producing a reduction of the Li-ion conductivity value on the order of 3 × 10 −7 S cm −1 (T s : 900°C) at 25°C [13].…”