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1. Halide Heterogeneous Structure Boosting Ionic Diffusion and High‐Voltage Stability of Sodium Superionic Conductors

   https://doi.org/10.1002/adma.202308012  

   Fu, Jiamin ; Wang, Shuo ; Wu, Duojie ; Luo, Jing ; Wang, Changhong ; Liang, Jianwen ; Lin, Xiaoting ; Hu, Yang ; Zhang, Shumin ; Zhao, Feipeng ; et al ( November 2023 , Advanced Materials)

   The development of solid‐state sodium‐ion batteries (SSSBs) heavily hinges on the development of an superionic Na⁺conductor (SSC) that features high conductivity, (electro)chemical stability, and deformability. The construction of heterogeneous structures offers a promising approach to comprehensively enhancing these properties in a way that differs from traditional structural optimization. Here, this work exploits the structural variance between high‐ and low‐coordination halide frameworks to develop a new class of halide heterogeneous structure electrolytes (HSEs). The halide HSEs incorporating a UCl₃‐type high‐coordination framework and amorphous low‐coordination phase achieves the highest Na⁺conductivity (2.7 mS cm⁻¹at room temperature, RT) among halide SSCs so far. By discerning the individual contribution of the crystalline bulk, amorphous region, and interface, this work unravels the synergistic ion conduction within halide HSEs and provides a comprehensive explanation of the amorphization effect. More importantly, the excellent deformability, high‐voltage stability, and expandability of HSEs enable effective SSSB integration. Using a cold‐pressed cathode electrode composite of uncoated Na_0.85Mn_0.5Ni_0.4Fe_0.1O₂and HSEs, the SSSBs present stable cycle performance with a capacity retention of 91.0% after 100 cycles at 0.2 C.

    

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2. Solid-State Electrochemical Synthesis of Silicon Clathrates Using a Sodium-Sulfur Battery Inspired Approach

   https://doi.org/10.1149/1945-7111/abdfe5  

   Dopilka, Andrew ; Childs, Amanda ; Bobev, Svilen ; Chan, Candace K. ( February 2021 , Journal of The Electrochemical Society)

   Clathrates of Tetrel elements (Si, Ge, Sn) have attracted interest for their potential use in batteries and other applications. Sodium-filled silicon clathrates are conventionally synthesized through thermal decomposition of the Zintl precursor Na₄Si₄, but phase selectivity of the product is often difficult to achieve. Herein, we report the selective formation of the type I clathrate Na₈Si₄₆using electrochemical oxidation at 450 °C and 550 °C. A two-electrode cell design inspired by high-temperature sodium-sulfur batteries is employed, using Na₄Si₄as working electrode, Naβ″-alumina solid electrolyte, and counter electrode consisting of molten Na or Sn. Galvanostatic intermittent titration is implemented to observe the oxidation characteristics and reveals a relatively constant cell potential under quasi-equilibrium conditions, indicating a two-phase reaction between Na₄Si₄and Na₈Si₄₆. We further demonstrate that the product selection and morphology can be altered by tuning the reaction temperature and Na vapor pressure. Room temperature lithiation of the synthesized Na₈Si₄₆is evaluated for the first time, showing similar electrochemical characteristics to those in the type II clathrate Na₂₄Si₁₃₆. The results show that solid-state electrochemical oxidation of Zintl phases at high temperatures can lead to opportunities for more controlled crystal growth and a deeper understanding of the formation processes of intermetallic clathrates.

    

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3. Sodium-based solid electrolytes and interfacial stability. Towards solid-state sodium batteries

   https://doi.org/doi.org/10.1016/j.mtcomm.2022.104009  

   Edelman, D A. ; Brandt, T. G. ; Temeche, E. ; Laine, R. M. ( July 2022 , Materials today communications)

   Electrochemical energy storage is a cost-effective, sustainable method for storing and delivering energy gener- ated from renewable resources. Among electrochemical energy storage devices, the lithium-ion battery (LIB) has dominated due to its high energy and power density. The success of LIBs has generated increased interest in sodium-ion battery (NaB) technology amid concerns of the sustainability and cost of lithium resources. In recent years, numerous studies have shown that sodium-ion solid-state electrolytes (NaSEs) have considerable potential to enable new cell chemistries that can deliver superior electrochemical performance to liquid-electrolyte-based NaBs. However, their commercial implementation is hindered by slow ionic transport at ambient and chemical/ mechanical incompatibility at interfaces. In this review, various NaSEs are first characterized based on individual crystal structures and ionic conduction mechanisms. Subsequently, selected methods of modifying interfaces in sodium solid-state batteries (NaSSBs) are covered, including anode wetting, ionic liquid (IL) addition, and composite polymer electrolytes (CPEs). Finally, examples are provided of how these techniques improve cycle life and rate performance of different cathode materials including sulfur, oxide, hexacyanoferrate, and phosphate-type. A focus on interfacial modification and optimization is crucial for realizing next-generation batteries. Thus, the novel methods reviewed here could pave the way toward a NaSSB capable of with- standing the high current and cycle life demands of future applications. 

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4. Electrochemical studies on Na-b"-alumina + yttria-stabilized zirconia (YSZ) composite mixed Na+ ion - O2- ion conductors

   Leila Ghadbeigi, Taylor D. ( June 2019 , Journal of the Electrochemical Society)

   Composite Na-”-alumina + yttria-stabilized zirconia (YSZ) samples were fabricated by vapor phase conversion of sintered -alumina + YSZ two-phase samples. In the converted samples Na-”-alumina and YSZ were both contiguous. The samples thus are mixed Na+-ion-O2--ion conductors. Discs were tested separately under an oxygen chemical potential differential (H2-H2O-N2 gas mixture on one side and air on the other – fuel cell mode) and under a sodium chemical potential differential (Na--alumina + Na-”-alumina on one side and -alumina + Na--alumina on the other side). In both cases finite open circuit voltages were measured. In testing in fuel cell mode, the initially observed open circuit voltage was lower than expected for a single phase YSZ membrane, which was attributed to the transient flow of Na+ ions. After prolonged testing, the surface exposed to hydrogen containing gas mixture degraded forming a thin layer of -alumina. The ionic conductivity of the samples was measured using both AC and DC methods. 

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5. Design Principles for Cation‐Mixed Sodium Solid Electrolytes

   https://doi.org/10.1002/aenm.202003196  

   Zhu, Zhuoying ; Tang, Hanmei ; Qi, Ji ; Li, Xiang‐Guo ; Ong, Shyue Ping ( January 2021 , Advanced Energy Materials)

   All‐solid‐state sodium‐ion batteries are highly promising for next generation grid energy storage with improved safety. Among the known sodium superionic conductors, the Na₃PnS₄family and the recently discovered Na₁₁Sn₂PnS₁₂(Pn = P, Sb) have garnered major interest due to their extremely high ionic conductivities. In this work, comprehensive investigation of the Na₃PnS₄‐Na₄TtS₄(Pn = P/As/Sb, Tt = Si/Ge/Sn) phase space of superionic conductors using density functional theory calculations, as well as AIMD simulations on the promising new Na₁₁Sn₂PnS₁₂(Pn=P/As/Sb) structures are presented. Crucial design rules on the effect of cation mixing are extracted on relative phase stability, electrochemical stability, moisture stability, and ionic conductivity. In particular, it is shown that while larger cations can substantially improve the ionic conductivity and moisture stability in these structures, there is an inherent trade‐off in terms of electrochemical stability. Na₁₁Sn₂AsS₁₂is also identified as a hitherto unexplored stable sodium superionic conductor with higher Na⁺conductivity and better moisture stability than the Na₁₁Sn₂PS₁₂and Na₁₁Sn₂SbS₁₂phases already reported experimentally.

    

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