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We report on the use of an atmospheric pressure, open-air plasma treatment to remove Li2CO3 species from the surface of garnet-type tantalum-doped lithium lanthanum zirconium oxide (Li6.4La3Zr1.4Ta0.6O12, LLZTO) solid-state electrolyte pellets. The Li2CO3 layer, which we show forms on the surface of garnets within 3 min of exposure to ambient moisture and CO2, increases the interface (surface) resistance of LLZTO. The plasma treatment is carried out entirely in ambient and is enabled by use of a custom-built metal shroud that is placed around the plasma nozzle to prevent moisture and CO2 from reacting with the sample. After the plasma treatment, N2 compressed gas is flowed through the shroud to cool the sample and prevent atmospheric species from reacting with the LLZTO. We demonstrate that this approach is effective for removing the Li2CO3 from the surface of LLZTO. The surface chemistry is characterized with X-ray photoelectron spectroscopy to evaluate the effect of process parameters (plasma exposure time and shroud gas chemistry) on removal of the surface species. We also show that the open-air plasma treatment can significantly reduce the interface resistance. This platform demonstrates a path towards open-air processed solid-state batteries. 

New structural insights into Li_7−xSn₂reveal partial/vacant Li occupancy. 

Type II germanium clathrates have recently been investigated for potential applications as anodes in batteries due to their cage-like structures that can accommodate electrochemical insertion of guest ions. To synthesize type II Ge clathrates (Ge136), several experimental routes use thermal or electrochemical desodiation of the Zintl phase compound Na4Ge4. However, the mechanism by which Na atoms are removed from the precursor to form clathrates is not well understood. Herein, we use first-principles density functional theory and nudged elastic band calculations to understand the reaction mechanism and formation energies of the products typically observed in the synthesis, namely, NaδGe136 (0 < δ < 24) type II clathrates and hexagonal phase Na1–xGe3+z. Specifically, we confirm the energetic feasibility of Na vacancy formation in Na4Ge4 and find that the barrier for Na vacancy migration is only 0.37 eV. This relatively low energy barrier is consistent with the ease with which Na4Ge4 can be desodiated to form the products. We also discuss the energetics, sodium migration pathways, and potential electrochemical performance of Ge136 as anode material for Na-ion batteries. Overall, this study highlights how first-principles calculations can be used to understand the synthesis mechanism and desodiation processes in clathrate materials and will help guide researchers in the design and evaluation of new open framework compounds as viable materials for energy storage applications. 

Lithium conducting garnets are attractive solid electrolytes for solid-state lithium batteries but are difficult to process, generally requiring high reaction and sintering temperatures with long durations. In this work, we demonstrate a synthetic route to obtain Ta-doped garnet (Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 ) utilizing La- and Ta-doped lanthanum zirconate (La 2.4 Zr 1.12 Ta 0.48 O 7.04 ) pyrochlore nanocrystals as quasi-single-source precursors. Via molten salt synthesis (MSS) in a highly basic flux, the pyrochlore nanocrystals transform to Li-garnet at reaction temperatures as low as 400 °C. We also show that the pyrochlore-to-garnet conversion can take place in one step using reactive sintering, resulting in densified garnet ceramics with high ionic conductivity (0.53 mS cm −1 at 21 °C) and relative density (up to 94.7%). This approach opens new avenues for lower temperature synthesis of lithium garnets using a quasi-single-source precursor and provides an alternative route to highly dense garnet solid electrolytes without requiring advanced sintering processes.