5 results
Search Results
Now showing 1 - 5 of 5
- ItemThe Electronic Conductivity of Single Crystalline Ga-Stabilized Cubic Li7La3Zr2O12: A Technologically Relevant Parameter for All-Solid-State Batteries(Weinheim : Wiley-VCH, 2020) Philipp, Martin; Gadermaier, Bernhard; Posch, Patrick; Hanzu, Ilie; Ganschow, Steffen; Meven, Martin; Rettenwander, Daniel; Redhammer, Günther J.; Wilkening, H. Martin R.The next-generation of all-solid-state lithium batteries need ceramic electrolytes with very high ionic conductivities. At the same time a negligible electronic conductivity σeon is required to eliminate self-discharge in such systems. A non-negligible electronic conductivity may also promote the unintentional formation of Li dendrites, being currently one of the key issues hindering the development of long-lasting all-solid-state batteries. This interplay is suggested recently for garnet-type Li7La3Zr2O12 (LLZO). It is, however, well known that the overall macroscopic electronic conductivity may be governed by a range of extrinsic factors such as impurities, chemical inhomogeneities, grain boundaries, morphology, and size effects. Here, advantage of Czochralski-grown single crystals, which offer the unique opportunity to evaluate intrinsic properties of a chemically homogeneous matrix, is taken to measure the electronic conductivity σeon. Via long-time, high-precision potentiostatic polarization experiments an upper limit of σeon in the order of 5 × 10−10 S cm−1 (293 K) is estimated. This value is by six orders of magnitude lower than the corresponding total conductivity σtotal = 10−3 S cm−1 of Ga-LLZO. Thus, it is concluded that the high values of σeon recently reported for similar systems do not necessarily mirror intragrain bulk properties of chemically homogenous systems but may originate from chemically inhomogeneous interfacial areas. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemLi+/H+ exchange of Li7La3Zr2O12 single and polycrystals investigated by quantitative LIBS depth profiling(Cambridge : Royal Society of Chemistry, 2022) Smetaczek, Stefan; Limbeck, Andreas; Zeller, Veronika; Ring, Joseph; Ganschow, Steffen; Rettenwander, Daniel; Fleig, JürgenLi7La3Zr2O12 (LLZO) garnets are highly attractive to be used as solid electrolyte in solid-state Li batteries. However, LLZO suffers from chemical interaction with air and humidity, causing Li+/H+ exchange with detrimental implication on its performance, processing and scalability. To better understand the kinetics of the detrimental Li+/H+ exchange and its dependence on microstructural features, accelerated Li+/H+ exchange experiments were performed on single crystalline and polycrystalline LLZO, exposed for 80 minutes to 80 °C hot water. The resulting chemical changes were quantified by analytical methods, i.e. inductively coupled plasma optical emission spectroscopy (ICP-OES) and laser induced breakdown spectroscopy (LIBS). From the time dependence of the Li+ enrichment in the water, measured by ICP-OES, a bulk interdiffusion coefficient of Li+/H+ could be determined (7 × 10−17 m2 s−1 at 80 °C). Depth dependent concentrations were obtained from the LIBS data for both ions after establishing a calibration method enabling not only Li+ but also H+ quantification in the solid electrolyte. Short interdiffusion lengths in the 1 μm range are found for the single crystalline Ga:LLZO, in accordance with the measured bulk diffusion coefficient. In polycrystalline Ta:LLZO, however, very long diffusion tails in the 20 μm range and ion exchange fractions up to about 70% are observed. Those are attributed to fast ion interdiffusion along grain boundaries. The severe compositional changes also strongly affect the electrical properties measured by impedance spectroscopy. This study highlights that microstructural effects may be decisive for the Li+/H+ ion exchange kinetics of LLZO.
- ItemThe natural critical current density limit for Li7La3Zr2O12 garnets(London [u.a.] : RSC, 2020) Flatscher, Florian; Philipp, Martin; Ganschow, Steffen; Wilkening, H. Martin R.; Rettenwander, DanielCeramic batteries equipped with Li-metal anodes are expected to double the energy density of conventional Li-ion batteries. Besides high energy densities, also high power is needed when batteries have to be developed for electric vehicles. Practically speaking, so-called critical current densities (CCD) higher than 3 mA cm-2 are needed to realize such systems. As yet, this value has, however, not been achieved for garnet-type Li7La3Zr2O12 (LLZO) being one of the most promising ceramic electrolytes. Most likely, CCD values are influenced by the area specific resistance (ASR) governing ionic transport across the Li|electrolyte interface. Here, single crystals of LLZO with adjusted ASR are used to quantify this relationship in a systematic manner. It turned out that CCD values exponentially decrease with increasing ASR. The highest obtained CCD value was as high as 280 µA cm-2. This value should be regarded as the room-temperature limit for LLZO when no external pressure is applied. Concluding, for polycrystalline samples either stack pressure or a significant increase of the interfacial area is needed to reach current densities equal or higher than the above-mentioned target value. This journal is © The Royal Society of Chemistry.
- ItemLithium metal penetration induced by electrodeposition through solid electrolytes: Example in single-crystal Li6La3ZrTaO12 garnet(Pennington, NJ : Electrochemical Society, 2018) Swamy, Tushar; Park, Richard; Sheldon, Brian W.; Rettenwander, Daniel; Porz, Lukas; Berendts, Stefan; Uecker, Reinhard; Carter, W. Craig; Chiang, Yet-MingSolid electrolytes potentially enable rechargeable batteries with lithium metal anodes possessing higher energy densities than today’s lithium ion batteries. To do so the solid electrolyte must suppress instabilities that lead to poor coulombic efficiency and short circuits. In this work, lithium electrodeposition was performed on single-crystal Li6La3ZrTaO12 garnets to investigate factors governing lithium penetration through brittle electrolytes. In single crystals, grain boundaries are excluded as paths for lithium metal propagation. Vickers microindentation was used to introduce surface flaws of known size. However, operando optical microscopy revealed that lithium metal penetration propagates preferentially from a different, second class of flaws. At the perimeter of surface current collectors smaller in size than the lithium source electrode, an enhanced electrodeposition current density causes lithium filled cracks to initiate and grow to penetration, even when large Vickers defects are in proximity. Modeling the electric field distribution in the experimental cell revealed that a 5-fold enhancement in field occurs within 10 micrometers of the electrode edge and generates high local electrochemomechanical stress. This may determine the initiation sites for lithium propagation, overriding the presence of larger defects elsewhere.
- ItemInvestigating the electrochemical stability of Li7La3Zr2O12 solid electrolytes using field stress experiments(London [u.a.] : RSC, 2021) Smetaczek, Stefan; Pycha, Eva; Ring, Joseph; Siebenhofer, Matthäus; Ganschow, Steffen; Berendts, Stefan; Nenning, Andreas; Kubicek, Markus; Rettenwander, Daniel; Limbeck, Andreas; Fleig, JürgenCubic Li7La3Zr2O12 (LLZO) garnets are among the most promising solid electrolytes for solid-state batteries with the potential to exceed conventional battery concepts in terms of energy density and safety. The electrochemical stability of LLZO is crucial for its application, however, controversial reports in the literature show that it is still an unsettled matter. Here, we investigate the electrochemical stability of LLZO single crystals by applying electric field stress via macro- and microscopic ionically blocking Au electrodes in ambient air. Induced material changes are subsequently probed using various locally resolved analysis techniques, including microelectrode electrochemical impedance spectroscopy (EIS), laser induced breakdown spectroscopy (LIBS), laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS), and microfocus X-ray diffraction (XRD). Our experiments indicate that LLZO decomposes at 4.1–4.3 V vs. Li+/Li, leading to the formation of Li-poor phases like La2Zr2O7 beneath the positively polarized electrode. The reaction is still on-going even after several days of polarization, indicating that no blocking interfacial layer is formed. The decomposition can be observed at elevated as well as room temperature and suggests that LLZO is truly not compatible with high voltage cathode materials.