Garnet Electrolytes for Solid State Batteries: Visualization of Moisture-Induced Chemical Degradation and Revealing Its Impact on the Li-Ion Dynamics

Abstract

In this work, we reveal the impact of moisture-induced chemical degradation and proton-lithium exchange on the Li-ion dynamics in the bulk, the grain boundaries and at the interface with lithium metal in highly Li-conducting garnet electrolytes. A direct correlation between chemical changes as measured by depth-resolved secondary ion mass spectrometry and the change in transport properties of the electrolyte is provided. In order to probe the intrinsic effect of the exchange on the lithium kinetics within the garnet structure, isolated from secondary corrosion product contributions, controlled-atmosphere processing was first used to produce proton-free Li6.55Ga0.15La3Zr2O12 (Ga0.15-LLZO), followed by degradation steps in a H2O bath at 100 C, leading to the removal of LiOH secondary phases at the surface. The proton-exchanged region was analysed by focussed ion beam-secondary ion mass spectrometry (FIB-SIMS) and 2 found to extend as far as 1.35 m into the Ga0.15-LLZO garnet pellet after 30 minutes in H2O. Impedance analysis in symmetrical cells with Li metal electrodes evidenced a greater reactivity in grain boundaries than in grains and a significantly detrimental effect on the Li transfer kinetics in the Li metal/garnet interface correlated to a threefold decrease in the Li mobility in the protonated garnet. This result evidences that the deterioration of Li charge transfer and diffusion kinetics in proton-containing garnet electrolytes have fundamental implications for the optimisation and integration of these systems in commercial battery devices.

Engineering of Sn and Pre‐Lithiated Sn as Negative Electrode Materials Coupled to Garnet Ta‐LLZO Solid Electrolyte for All‐Solid‐State Li Batteries

“…During the first delithiation, the retrieved specific charge was limited to 50 mAh/g (only 30 mAh/g without the potentiostatic step). These poor electrochemical results can be explained by several factors such as i) the poor interfacial contact between the electrode and the solid electrolyte (separator), ii) phases generated at the interface between Sn/LLZTa creating an insulating layer (Li 2 CO 3 and unknown impurities), and iii) the lithiation of the Sn particles that can generate volume change of more than 300 % leads to particles’ fracture and most probably “film pilling of” and particles disconnection, as already reported . As a consequence, the following cycles are presenting very poor electrochemical performance since we were unable to exceed 15 mAh/g in galvanostatic mode, corresponding to less than 2 % of the expected theoretical specific charge.…”

“…To this point, we investigated two main strategies to prepare the electrode either by a slurry‐based process or by thin film sputtering. The former is more appealing, especially for bulk‐type batteries, as the engineering is rather simple but it turns out that the garnet is reacting strongly with the solvent used to make the slurry (detectable via X‐ray diffraction (XRD) and SEM‐cross section experiments), as reported already in the literature, and that the electroactive materials should be in the form of nanoparticles to ensure proper electronic conductivity . By using operando XRD measurements, we found out that Sn particles are properly lithiated during the first cycle.…”

Lithium Garnet Li7La3Zr2O12 Electrolyte for All‐Solid‐State Batteries: Closing the Gap between Bulk and Thin Film Li‐Ion Conductivities

“…On the surface, the 7 Li + signal is significantly higher, likely due to the presence of lithium hydroxide as a result of exposure to air while loading the samples into the measurement system. [31,32] Regarding the distribution of the dopant, only Al could be investigated due to the use of a Ga ion beam for sputtering. In the Al-doped LLZO film, the 27 Al + signal appears homogeneously distributed in the film, both in depth and over the lateral plane.…”

Germanium as a donor dopant in garnet electrolytes

“…A series of Li7-4xGexLa3Zr2O12 compounds with nominal Ge concentrations (x) of 0.05, 0.10, 0.15, 0.30 and 0.50 a.p.f.u were prepared by the modified sol-gel route described previously for Ga-doped LLZO. 13,27 GeO2 (99.98%), LiNO3 (99%), La2(NO3)3x6H2O (99.9 %) and Zr(IV) 2,4-pentanedionate C20H28O8 (99.99%) (all Alfa Aesar) were used as reagents and dissolved in citric acid (10 wt%, equivalent to 0.542 M, approx. 200 ml, Sigma Aldrich) and a small amount of nitric acid to aid dissolution (68 wt%, approx.…”

“…The green pellets were surrounded by a bed of the mother powder to reduce Li2O loss. All processing steps (milling, pellet forming) were carried out in an argon atmosphere glove box (<0.3 ppm H2O, <10 ppm O2) to prevent degradation processes associated with proton-lithium exchange in humid atmosphere 27 . Prior to analysis, pellets of the material were polished with progressively fine SiC grit paper to 4000 grit finish.…”