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1. Recent Progress on Dominant Sulfide‐Type Solid‐State Na Superionic Conductors for Solid‐State Sodium Batteries

   https://doi.org/10.1002/smll.202311195  

   Guo, Xiaolin; Halacoglu, Selim; Chen, Yan; Wang, Hui (May 2024, Small)

   Abstract Over the past decade, solid‐state batteries have garnered significant attentions due to their potentials to deliver high energy density and excellent safety. Considering the abundant sodium (Na) resources in contrast to lithium (Li), the development of sodium‐based batteries has become increasingly appealing. Sulfide‐based superionic conductors are widely considered as promising solid eletcrolytes (SEs) in solid‐state Na batteries due to the features of high ionic conductivity and cold‐press densification. In recent years, tremendous efforts have been made to investigate sulfide‐based Na‐ion conductors on their synthesis, compositions, conductivity, and the feasibility in batteries. However, there are still several challenges to overcome for their practical applications in high performance solid‐state Na batteries. This article provides a comprehensive update on the synthesis, structure, and properties of three dominant sulfide‐based Na‐ion conductors (Na₃PS₄, Na₃SbS₄, and Na₁₁Sn₂PS₁₂), and their families that have a variety of anion and cation doping. Additionally, the interface stability of these sulfide electrolytes toward the anode is reviewed, as well as the electrochemical performance of solid‐state Na batteries based on different types of cathode materials (metal sulfides, oxides, and organics). Finally, the perspective and outlook for the development and practical utilization of sulfide‐based SE in solid‐state batteries are discussed. 

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2. Aprotic Alkali Metal−O2 Batteries: Role of Cathode Surface-Mediated Processes and Heterogeneous Electrocatalysis

   https://doi.org/10.1021/acsenergylett.0c02506  

   Samji Samira, Siddharth Deshpande (January 2021, ACS energy letters)

   Alkali metal–O2 batteries (i.e., Li/Na–O2) with high specific energies are promising alternatives to state-of-the-art metal-ion batteries. However, they are plagued by challenges arising from the underlying redox chemistry, resulting in reduced efficiencies. These challenges for Li/Na–O2 batteries stem from the nature of the interface between solid discharge product(s) and either (i) the aprotic electrolyte or (ii) the solid cathode. In the former, the reactive nature of the solid/liquid interface leads to chemical disproportionation of the discharge product(s) and the electrolyte, while in the latter, the presence/lack of atomistic interactions at the solid–solid interface leads to large overpotential losses (>1 V) during charging. Approaches to overcome these challenges would involve decoupling these factors. For instance, the use of inert aprotic electrolytes would facilitate catalytically driven, surface-mediated discharge product(s) growth, providing avenues to use cathode surface modifications as levers to enhance voltaic efficiency and discharge product stability, resulting in improved performance. 

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3. Universal Cathode Design Strategies to Engineer Cathode Electrolyte Interfaces for High Performance All-Solid-State Batteries

   Zhang, Yuxuan; Song, Han Wook; Lee, Sunghwan (May 2022, Materials Research Society)

   Metal-ion batteries (e.g., lithium and sodium ion batteries) are the promising power sources for portable electronics, electric vehicles, and smart grids. Recent metal-ion batteries with organic liquid electrolytes still suffer from safety issues regarding inflammability and insufficient lifetime.1 As the next generation energy storage devices, all-solid-state batteries (ASSBs) have promising potentials for the improved safety, higher energy density, and longer cycle life than conventional Li-ion batteries.2 The nonflammable solid electrolytes (SEs), where only Li ions are mobile, could prevent battery combustion and explosion since the side reactions that cause safety issues as well as degradation of the battery performance are largely suppressed. However, their practical application is hampered by the high resistance arising at the solid–solid electrode–electrolyte interface (including cathode-electrolyte interface and anode-electrolyte interface).3 Several methods have been introduced to optimize the contact capability as well as the electrochemical/chemical stability between the metal anodes (i.e.: Li and Na) and the SEs, which exhibited decent results in decreasing the charge transfer resistance and broadening the range of the stable energy window (i.e., lowing the chemical potential of metal anode below the highest occupied molecular orbital of the SEs).4 Nevertheless, mitigation for the cathode in ASSB is tardily developed because: (1) the porous structure of the cathode is hard to be infiltrated by SEs;5 (2) SEs would be oxidized and decomposed by the high valence state elements at the surface of the cathode at high state of charge.5 Herein, we demonstrate a universal cathode design strategy to achieve superior contact capability and high electrochemical/chemical stability with SEs. Stereolithography is adopted as a manufacturing technique to realize a hierarchical three-dimensional (HTD) electrode architecture with micro-size channels, which is expected to provide larger contact areas with SEs. Then, the manufactured cathode is sintered at 700 °C in a reducing atmosphere (e.g.: H2) to accomplish the carbonization of the resin, delivering sufficiently high electronic conductivity for the cathode. To avoid the direct exposure of the cathode active materials to the SEs, oxidative chemical vapor deposition technique (oCVD) is leveraged to build conformal and highly conducting poly(3,4-ethylenedioxythiophene) (PEDOT) on the surface of the HTD cathode.6 To demonstrate our design strategy, both NCM811 and Na3V2(PO4)3 is selected as active materials in the HTD cathode, then each cathode is paired with organic (polyacrylonitrile-based) and inorganic (sulfur-based) SEs assembled into two batteries (total four batteries). SEM and TEM reveal the micro-size HTD structure with built-in channels. Featured by the HTD architecture, the intrinsic kinetic and thermodynamic conditions will be enhanced by larger surface contact areas, more active sites, improved infusion and electrolyte ion accessibility, and larger volume expansion capability. Disclosed by X-ray computed tomography, the interface between cathode and SEs in the four modified samples demonstrates higher homogeneity at the interface between the cathode and SEs than that of all other pristine samples. Atomic force microscopy is employed to measure the potential image of the cross-sectional interface by the peak force tapping mode. The average potential of modified samples is lower than that of pristine samples, which confirms a weakened space charge layer by the enhanced contact capability. In addition, through Electron Energy Loss Spectroscopy coupled with Scanning Transmission Electron Microscopy, the preserved interface between HTD cathode and SE is identified; however, the decomposing of the pristine cathode is clearly observed. In addition, Finite element method simulations validate that the diffusion dynamics of lithium ions is favored by HTD structure. Such a demonstrated universal strategy provides a new guideline to engineer cathode electrolyte interface by reconstructing electrode structures that can be applicable to all solid-state batteries in a wide range of chemical conditions. 

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4. Self‐Templated 3D Sulfide‐Based Solid Composite Electrolyte for Solid‐State Sodium Metal Batteries

   https://doi.org/10.1002/smll.202406298  

   Guo, Xiaolin; Li, Yang; Halacoglu, Selim; Graff, Kincaid; Zhang, Chunyan; Fu, Kelvin; Xiong, Hui_Claire; Wang, Hui (October 2024, Small)

   Abstract Rechargeable solid‐state sodium metal batteries (SSMBs) experience growing attention owing to the increased energy density (vs Na‐ion batteries) and cost‐effective materials. Inorganic sulfide‐based Na‐ion conductors also possess significant potential as promising solid electrolytes (SEs) in SSMBs. Nevertheless, due to the highly reactive Na metal, poor interface compatibility is the biggest obstacle for inorganic sulfide solid electrolytes such as Na₃SbS₄to achieve high performance in SSMBs. To address such electrochemical instability at the interface, new design of sulfide SE nanostructures and interface engineering are highly essential. In this work, a facile and straightforward approach is reported to prepare 3D sulfide‐based solid composite electrolytes (SCEs), which utilize porous Na₃SbS₄(NSS) as a self‐templated framework and fill with a phase transition polymer. The 3D structured SCEs display obviously improved interface stability toward Na metal than pristine sulfide. The assembled SSMBs (with TiS₂or FeS₂as cathodes) deliver outstanding electrochemical cycling performance. Moreover, the cycling of high‐voltage oxide cathode Na_0.67Ni_0.33Mn_0.67O₂(NNMO) is also demonstrated in SSMBs using 3D sulfide‐based SCEs. This study presents a novel design on the self‐templated nanostructure of SCEs, paving the way for the advancement of high‐energy sodium metal batteries. 

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5. High-performance all-solid-state batteries enabled by salt bonding to perovskite in poly(ethylene oxide)

   https://doi.org/10.1073/pnas.1907507116  

   Xu, Henghui; Chien, Po-Hsiu; Shi, Jianjian; Li, Yutao; Wu, Nan; Liu, Yuanyue; Hu, Yan-Yan; Goodenough, John B. (September 2019, Proceedings of the National Academy of Sciences)

   Flexible and low-cost poly(ethylene oxide) (PEO)-based electrolytes are promising for all-solid-state Li-metal batteries because of their compatibility with a metallic lithium anode. However, the low room-temperature Li-ion conductivity of PEO solid electrolytes and severe lithium-dendrite growth limit their application in high-energy Li-metal batteries. Here we prepared a PEO/perovskite Li 3/8 Sr 7/16 Ta 3/4 Zr 1/4 O 3 composite electrolyte with a Li-ion conductivity of 5.4 × 10 −5 and 3.5 × 10 −4 S cm −1 at 25 and 45 °C, respectively; the strong interaction between the F − of TFSI − (bis-trifluoromethanesulfonimide) and the surface Ta 5+ of the perovskite improves the Li-ion transport at the PEO/perovskite interface. A symmetric Li/composite electrolyte/Li cell shows an excellent cyclability at a high current density up to 0.6 mA cm −2 . A solid electrolyte interphase layer formed in situ between the metallic lithium anode and the composite electrolyte suppresses lithium-dendrite formation and growth. All-solid-state Li|LiFePO 4 and high-voltage Li|LiNi 0.8 Mn 0.1 Co 0.1 O 2 batteries with the composite electrolyte have an impressive performance with high Coulombic efficiencies, small overpotentials, and good cycling stability. 

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