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1. Pyrochlore nanocrystals as versatile quasi-single-source precursors to lithium conducting garnets

   https://doi.org/10.1039/d0ta05842d  

   Weller, J. Mark ; Chan, Candace K. ( September 2020 , Journal of Materials Chemistry A)

   null (Ed.)

   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. 

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2. Lithium Ion Pathway within Li 7 La 3 Zr 2 O 12 ‐Polyethylene Oxide Composite Electrolytes

   https://doi.org/10.1002/ange.201607539  

   Zheng, Jin ; Tang, Mingxue ; Hu, Yan‐Yan ( September 2016 , Angewandte Chemie)

   Polymer–ceramic composite electrolytes are emerging as a promising solution to deliver high ionic conductivity, optimal mechanical properties, and good safety for developing high‐performance all‐solid‐state rechargeable batteries. Composite electrolytes have been prepared with cubic‐phase Li₇La₃Zr₂O₁₂(LLZO) garnet and polyethylene oxide (PEO) and employed in symmetric lithium battery cells. By combining selective isotope labeling and high‐resolution solid‐state Li NMR, we are able to track Li ion pathways within LLZO‐PEO composite electrolytes by monitoring the replacement of⁷Li in the composite electrolyte by⁶Li from the⁶Li metal electrodes during battery cycling. We have provided the first experimental evidence to show that Li ions favor the pathway through the LLZO ceramic phase instead of the PEO‐LLZO interface or PEO. This approach can be widely applied to study ion pathways in ionic conductors and to provide useful insights for developing composite materials for energy storage and harvesting.

    

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3. A Highly Efficient All‐Solid‐State Lithium/Electrolyte Interface Induced by an Energetic Reaction

   https://doi.org/10.1002/anie.202004477  

   Zhong, Yiren ; Xie, Yujun ; Hwang, Sooyeon ; Wang, Qian ; Cha, Judy J. ; Su, Dong ; Wang, Hailiang ( June 2020 , Angewandte Chemie International Edition)

   The energetic chemical reaction between Zn(NO₃)₂and Li is used to create a solid‐state interface between Li metal and Li_6.4La₃Zr_1.4Ta_0.6O₁₂(LLZTO) electrolyte. This interlayer, composed of Zn, ZnLi_xalloy, Li₃N, Li₂O, and other species, possesses strong affinities with both Li metal and LLZTO and affords highly efficient conductive pathways for Li⁺transport through the interface. The unique structure and properties of the interlayer lead to Li metal anodes with longer cycle life, higher efficiency, and better safety compared to the current best Li metal electrodes operating in liquid electrolytes while retaining comparable capacity, rate, and overpotential. All‐solid‐state Li||Li cells can operate at very demanding current–capacity conditions of 4 mA cm⁻²–8 mAh cm⁻². Thousands of hours of continuous cycling are achieved at Coulombic efficiency >99.5 % without dendrite formation or side reactions with the electrolyte.

    

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4. A Highly Efficient All‐Solid‐State Lithium/Electrolyte Interface Induced by an Energetic Reaction

   https://doi.org/10.1002/ange.202004477  

   Zhong, Yiren ; Xie, Yujun ; Hwang, Sooyeon ; Wang, Qian ; Cha, Judy J. ; Su, Dong ; Wang, Hailiang ( June 2020 , Angewandte Chemie)

   The energetic chemical reaction between Zn(NO₃)₂and Li is used to create a solid‐state interface between Li metal and Li_6.4La₃Zr_1.4Ta_0.6O₁₂(LLZTO) electrolyte. This interlayer, composed of Zn, ZnLi_xalloy, Li₃N, Li₂O, and other species, possesses strong affinities with both Li metal and LLZTO and affords highly efficient conductive pathways for Li⁺transport through the interface. The unique structure and properties of the interlayer lead to Li metal anodes with longer cycle life, higher efficiency, and better safety compared to the current best Li metal electrodes operating in liquid electrolytes while retaining comparable capacity, rate, and overpotential. All‐solid‐state Li||Li cells can operate at very demanding current–capacity conditions of 4 mA cm⁻²–8 mAh cm⁻². Thousands of hours of continuous cycling are achieved at Coulombic efficiency >99.5 % without dendrite formation or side reactions with the electrolyte.

    

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5. Elastic Modulus, Hardness, and Fracture Toughness of Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 Solid Electrolyte

   https://doi.org/10.1088/0256-307X/38/9/098401  

   Hu, Shan ; Xu, Pengyu ; de Vasconcelos, Luize Scalco ; Stanciu, Lia ; Ni, Hongwei ; Zhao, Kejie ( October 2021 , Chinese Physics Letters)

   Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) is a promising inorganic solid electrolyte due to its high Li + conductivity and electrochemical stability for all-solid-state batteries. Mechanical characterization of LLZTO is limited by the synthesis of the condensed phase. Here we systematically measure the elastic modules, hardness, and fracture toughness of LLZTO polycrystalline pellets of different densities using the customized environmental nanoindentation. The LLZTO samples are sintered using the hot-pressing method with different amounts of Li 2 CO 3 additives, resulting in the relative density of the pellets varying from 83% to 98% and the largest grain size of 13.21 ± 5.22 μm. The mechanical properties show a monotonic increase as the sintered sample densifies, elastic modulus and hardness reach 158.47 ± 10.10 GPa and 11.27 ± 1.38 GPa, respectively, for LLZTO of 98% density. Similarly, fracture toughness increases from 0.44 to 1.51 MPa⋅m 1/2 , showing a transition from the intergranular to transgranular fracture behavior as the pellet density increases. The ionic conductivity reaches 4.54 × 10 −4 S/cm in the condensed LLZTO which enables a stable Li plating/stripping in a symmetric solid-state cell for over 100 cycles. This study puts forward a quantitative study of the mechanical behavior of LLZTO of different microstructures that is relevant to the mechanical stability and electrochemical performance of all-solid-state batteries. 

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