ESRF Highlights 2023

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9 3 I H I G H L I G H T S 2 0 2 3

PRINCIPAL PUBLICATION AND AUTHORS

Bilayer Dense-Porous Li7La3Zr2O12 Membranes for High-Performance Li-Garnet Solid-State Batteries, H. Zhang (a,b), F. Okur (a,b), C. Cancellieri (c), L.P.H. Jeurgens (c), A. Parrilli (d), D.T. Karabay (a,b), M. Nesvadba (a,b), S. Hwang (a,b), A. Neels (d), M.V. Kovalenko (a,b), K.V. Kravchyk (a,b), Adv. Sci. 8, 2205821 (2023); https:/doi.org/10.1002/advs.202205821 (a) Department of Chemistry and Applied Biosciences, ETH Zürich, Zürich (Switzerland) (b) Laboratory for Thin Films and Photovoltaics, Empa, Dübendorf (Switzerland) (c) Laboratory for Joining Technologies & Corrosion, Empa, Dübendorf (Switzerland) (d) Center for X-Ray Analytics, Empa, Dübendorf (Switzerland)

REFERENCES

[1] K.V. Kravchyk et al., Sci. Rep. 12, 1177 (2022). [2] K. Fu et al., Energy Environ. Sci. 10, 1568-1575 (2017).

that in the case of using LLZO powder without the addition of Li2CO3, the sintered LLZO membranes contained large quantities of La2Zr2O7 (LZO). To understand the chemical transformations that occur during de-binding and sintering of tape-casted LLZO tapes, the tapes were analysed by in-situ synchrotron X-ray diffraction (XRD) at beamline BM01. The experiments revealed that multiple chemical processes occur (Figure 70d-e). First, the de- binding causes the formation of a relatively large quantity of the LZO phase, as follows from the comparison of as- prepared LLZO tape and de-binded LLZO membranes. Upon a further increase of temperature to 760°C, however, the intensity of LZO reflections starts to disappear, resulting in the formation of a solely cubic LLZO structure. This process is accompanied by the disappearance of the Li2CO3 peak at ≈716°C, which is likely associated with the melting of Li2CO3, decomposition to Li2O and following reaction with LZO. Importantly, membranes with higher Li2CO3 content were observed to have higher density. This observation is in line with the reported impact of Li2CO3 on the densification of LLZO pellets. It is assumed that this effect is related to the melting of Li2CO3, which makes it possible to initiate the sintering process at lower temperatures. LLZO ceramics without additional Li2CO3 require a higher temperature and longer time for sintering, potentially causing huge Li loss.

After extra-thermal surface treatments to clean the impurities on the LLZO membrane, the electrochemical functionality of the developed bi-layered dense porous LLZO scaffolds was investigated in full hybrid-type cells in combination with a paste-type lithium ion phosphate (LFP) cathode (as a proof-of-concept battery in Figure 71a-b). Figure 71c-d shows the voltage profiles and cycling stability measurements of an LFP/LLZO/Li full cell measured at 0.1 C rate. The cell delivered the capacity of LFP of ≈100-150 mAh g−1, which corresponds to the areal capacity of ≈0.3- 0.45 mAh cm−2. The results demonstrate a relatively low capacity retention of 65% after 30 cycles. Besides, in symmetrical cell configuration, the LLZO membranes exhibit a high critical current density (6 mA cm−2), low overpotentials (14-16 mV at 1.0 mA cm−2), and excellent Li plating/stripping cycling stability (over 160 cycles at 0.5 mA cm−2 with a 0.25 mAh cm−2 areal capacity limitation.

In summary, this work reports a methodology for manufacturing dense porous LLZO membranes with thicknesses maximally close to those required for achieving high gravimetric and volumetric energy densities of Li-garnet solid-state batteries, and contributes to enabling their eventual commercialisation.

Fig. 71: a-b) Schematics of the charging process of Li-garnet solid-state batteries based on dense porous LLZO membrane. Galvanostatic charge-discharge (c) voltage profiles and (d) cyclic stability of LFP/LLZO membrane/ Li full cells measured at 0.1 C rate and room temperature without the employment of external pressure.