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1. Poor Stability of Li ₂ CO ₃ in the Solid Electrolyte Interphase of a Lithium‐Metal Anode Revealed by Cryo‐Electron Microscopy

   https://doi.org/10.1002/adma.202100404  

   Han, Bing; Zhang, Zhen; Zou, Yucheng; Xu, Kang; Xu, Guiyin; Wang, Hong; Meng, Hong; Deng, Yonghong; Li, Ju; Gu, Meng (April 2021, Advanced Materials)

   Abstract The solid electrolyte interphase (SEI) dictates the cycling stability of lithium‐metal batteries. Here, direct atomic imaging of the SEI's phase components and their spatial arrangement is achieved, using ultralow‐dosage cryogenic transmission electron microscopy. The results show that, surprisingly, a lot of the deposited Li metal has amorphous atomic structure, likely due to carbon and oxygen impurities, and that crystalline lithium carbonate is not stable and readily decomposes when contacting the lithium metal. Lithium carbonate distributed in the outer SEI also continuously reacts with the electrolyte to produce gas, resulting in a dynamically evolving and porous SEI. Sulfur‐containing additives cause the SEI to preferentially generate Li₂SO₄and overlithiated lithium sulfate and lithium oxide, which encapsulate lithium carbonate in the middle, limiting SEI thickening and enhancing battery life by a factor of ten. The spatial mapping of the SEI gradient amorphous (polymeric → inorganic → metallic) and crystalline phase components provides guidance for designing electrolyte additives. 

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2. Lithium‐Ion Mobility in Layered Oxide Li ₂ (La _0.75 Li _0.25 )(Ta _1.5 Ti _0.5 )O ₇ Containing Lithium on both Intra and Inter‐Stack Positions

   https://doi.org/10.1002/ejic.202100950  

   Fanah, Selorm_Joy; Ramezanipour, Farshid (February 2022, European Journal of Inorganic Chemistry)

   Abstract With the aid of neutron diffraction and electrochemical impedance spectroscopy, we have demonstrated the effect of the increase in lithium concentration and distribution on Li‐ion conductivity. This has been done through the synthesis of a layered oxide Li₂(La_0.75Li_0.25)(Ta_1.5Ti_0.5)O₇, with the so‐called Ruddlesden‐Popper type structure, where bilayer stacks of (Ta/Ti)O₆octahedra are separated by lithium ions, located in inter‐stack spaces. There are also intra‐stack spaces that are occupied by a mixture of La and Li, as confirmed by neutron diffraction. The distribution of lithium over both inter‐ and intra‐stack positions leads to the enhancement of Li‐ion conductivity in Li₂(La_0.75Li_0.25)(Ta_1.5Ti_0.5)O₇compared to Li₂La(TaTi)O₇, which has a lower concentration of lithium ions, located only in inter‐stack spaces. The analyses of real and imaginary components of electrochemical impedance data confirm the enhanced mobility of ions in Li₂(La_0.75Li_0.25)(Ta_1.5Ti_0.5)O₇. While the Li‐ion conductivity needs further improvement for practical applications, the success of the strategy implemented in this work offers a useful methodology for the design of layered ionic conductors. 

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3. A room temperature rechargeable Li ₂ O-based lithium-air battery enabled by a solid electrolyte

   https://doi.org/10.1126/science.abq1347  

   Kondori, Alireza; Esmaeilirad, Mohammadreza; Harzandi, Ahmad Mosen; Amine, Rachid; Saray, Mahmoud Tamadoni; Yu, Lei; Liu, Tongchao; Wen, Jianguo; Shan, Nannan; Wang, Hsien-Hau; et al (February 2023, Science)

   A lithium-air battery based on lithium oxide (Li₂O) formation can theoretically deliver an energy density that is comparable to that of gasoline. Lithium oxide formation involves a four-electron reaction that is more difficult to achieve than the one- and two-electron reaction processes that result in lithium superoxide (LiO₂) and lithium peroxide (Li₂O₂), respectively. By using a composite polymer electrolyte based on Li₁₀GeP₂S₁₂nanoparticles embedded in a modified polyethylene oxide polymer matrix, we found that Li₂O is the main product in a room temperature solid-state lithium-air battery. The battery is rechargeable for 1000 cycles with a low polarization gap and can operate at high rates. The four-electron reaction is enabled by a mixed ion–electron-conducting discharge product and its interface with air. 

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4. NASICON Li _1.2 Mg _0.1 Zr _1.9 (PO ₄ ) ₃ Solid Electrolyte for an All‐Solid‐State Li‐Metal Battery

   https://doi.org/10.1002/smtd.202000764  

   Zhou, Qiongyu; Xu, Biyi; Chien, Po‐Hsiu; Li, Yutao; Huang, Bing; Wu, Nan; Xu, Henghui; Grundish, Nicholas S.; Hu, Yan‐Yan; Goodenough, John B. (September 2020, Small Methods)

   Abstract A thin solid electrolyte with a high Li⁺conductivity is used to separate the metallic lithium anode and the cathode in an all‐solid‐state Li‐metal battery. However, most solid Li‐ion electrolytes have a small electrochemical stability window, large interfacial resistance, and cannot block lithium‐dendrite growth when lithium is plated on charging of the cell. Mg²⁺stabilizes a rhombohedral NASICON‐structured solid electrolyte of the formula Li_1.2Mg_0.1Zr_1.9(PO₄)₃(LMZP). This solid electrolyte has Li‐ion conductivity two orders of magnitude higher at 25 °C than that of the triclinic LiZr₂(PO₄)₃.⁷Li and⁶Li NMR confirm the Li‐ions in two different crystallographic sites of the NASICON framework with 85% of the Li‐ions having a relatively higher mobility than the other 15%. The anode–electrolyte interface is further investigated with symmetric Li/LMZP/Li cell testing, while the cathode–electrolyte interface is explored with an all‐solid‐state Li/LMZP/LiFePO₄cell. The enhanced performance of these cells enabled by the Li_1.2Mg_0.1Zr_1.9(PO₄)₃solid electrolyte is stable upon repeated charge/discharge cycling. 

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5. Importance of multimodal characterization and influence of residual Li ₂ S impurity in amorphous Li ₃ PS ₄ inorganic electrolytes

   https://doi.org/10.1039/d1ta02754a  

   Mirmira, Priyadarshini; Zheng, Jin; Ma, Peiyuan; Amanchukwu, Chibueze V. (September 2021, Journal of Materials Chemistry A)

   Amorphous Li 3 PS 4 (LPS) solid-state electrolytes are promising for energy-dense lithium metal batteries. LPS glass, synthesized from a 3 : 1 mol ratio of Li 2 S and P 2 S 5 , has high ionic conductivity and can be synthesized by ball milling or solution processing. Ball milling has been attractive because it provides the easiest route to access amorphous LPS with a conductivity of 3.5 × 10 −4 S cm −1 (20 °C). However, achieving the complete reaction of precursors via ball milling can be difficult, and most literature reports use X-ray diffraction (XRD) or Raman spectroscopy to confirm sample purity, both of which have limitations. Furthermore, the effect of residual precursors on ionic conductivity and lithium metal cycling is unknown. In this work, we illustrate the importance of multimodal characterization to determine LPS phase and chemical purity. To determine the residual Li 2 S content in LPS, we show that (1) XRD and 31 P solid state nuclear magnetic resonance (ssNMR) are insufficient and (2) Raman loses sensitivity at concentrations below 12 mol% Li 2 S. Most importantly, we show that 7 Li ssNMR is highly sensitive. Using 7 Li ssNMR, we investigate the effect of ball milling parameters and develop a robust and highly reproducible procedure for pure LPS synthesis. We find that as the residual Li 2 S precursor content increases, LPS conductivity decreases and lithium metal batteries exhibit higher overpotentials and poor cycle life. Our work reveals the importance of multimodal characterization techniques for amorphous solid-state electrolyte characterization and will enable better synthetic strategies for highly conductive electrolytes for efficient energy-dense solid-state lithium metal batteries. 

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