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1. Lithium-activated SnS–graphene alternating nanolayers enable dendrite-free cycling of thin sodium metal anodes in carbonate electrolyte

   https://doi.org/10.1039/d0ee02423f  

   Liu, Wei ; Chen, Zidong ; Zhang, Zheng ; Jiang, Pingxian ; Chen, Yungui ; Paek, Eunsu ; Wang, Yixian ; Mitlin, David ( January 2021 , Energy & Environmental Science)

   null (Ed.)

   Sodium metal battery (SMB, NMB) anodes can become dendritic due to an electrochemically unstable native Na-based solid electrolyte interphase (SEI). Herein Li-ion activated tin sulfide graphene nanocomposite membrane (A-SnS–G) is employed as an artificial SEI layer, allowing cyclability of record-thin 100 μm Na metal foils. The thin Na metal is prepared by a self-designed metallurgical rolling protocol. A-SnS–G is initially placed onto the polypropylene (PP) separator but becomes in situ transferred onto the Na metal surface. Symmetric metal cells protected by A-SnS–G achieve low-overpotential extended high-rate cycling in a standard carbonate electrolyte (EC : DEC = 1 : 1, 5% FEC). Accumulated capacity of 1000 mA h cm −2 is obtained after 500 cycles at 4 mA cm −2 , with accumulated capacity-to-foil capacity (A/F) ratio of 90.9. This is among the most favorable cycle life, accumulated capacity, and anode utilization combinations reported. Protection by non-activated SnS–G membrane yields significantly worse cycling, albeit still superior to the baseline unprotected sodium. Post-mortem and dedicated light optical analysis indicate that metal swelling, dendrite growth and dead metal formation is extensive for the unprotected sample, but is suppressed with A-SnS–G. Per XPS, post-100 cycles near-surface structure of A-SnS–G is rich in metallic Sn alloys and inorganic carbonate salts. Even after 300 cycles, Li-based SEI components ROCO 2 -Li, Li 2 CO 3 and LiF are detected with A-SnS–G. As a proof of principle, an SMB with a high mass loading (6 mg cm −2 ) NVP cathode and a A-SnS–G protected anode delivered extended cyclability, achieving 74 mA h g −1 after 400 cycles at 0.4C. 

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2. Making Plasticized Polymer Electrolytes Stable Against Sodium Metal for High‐Energy Solid‐State Sodium Batteries

   https://doi.org/10.1002/anie.202319427  

   Zou, Peichao ; Wang, Chunyang ; He, Yubin ; Xin, Huolin L. ( March 2024 , Angewandte Chemie International Edition)

   Solid polymer electrolytes based on plastic crystals are promising for solid‐state sodium metal (Na⁰) batteries, yet their practicality has been hindered by the notorious Na⁰‐electrolyte interface instability issue, the underlying cause of which remains poorly understood. Here, by leveraging a model plasticized polymer electrolyte based on conventional succinonitrile plastic crystals, we uncover its failure origin in Na⁰batteries is associated with the formation of a thick and non‐uniform solid electrolyte interphase (SEI) and whiskery Na⁰nucleation/growth. Furthermore, we design a new additive‐embedded plasticized polymer electrolyte to manipulate the Na⁰deposition and SEI formulation. For the first time, we demonstrate that introducing fluoroethylene carbonate (FEC) additive into the succinonitrile‐plasticized polymer electrolyte can effectively protect Na⁰against interfacial corrosion by facilitating the growth of dome‐like Na⁰with thin, amorphous, and fluorine‐rich SEIs, thus enabling significantly improved performances of Na//Na symmetric cells (1,800 h at 0.5 mA cm⁻²) and Na//Na₃V₂(PO₄)₃full cells (93.0 % capacity retention after 1,200 cycles at 1 C rate in coin cells and 93.1 % capacity retention after 250 cycles at C/3 in pouch cells at room temperature). Our work provides valuable insights into the interfacial failure of plasticized polymer electrolytes and offers a promising solution to resolving the interfacial instability issue.

    

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3. Making Plasticized Polymer Electrolytes Stable Against Sodium Metal for High‐Energy Solid‐State Sodium Batteries

   https://doi.org/10.1002/ange.202319427  

   Zou, Peichao ; Wang, Chunyang ; He, Yubin ; Xin, Huolin L. ( March 2024 , Angewandte Chemie)

   Solid polymer electrolytes based on plastic crystals are promising for solid‐state sodium metal (Na⁰) batteries, yet their practicality has been hindered by the notorious Na⁰‐electrolyte interface instability issue, the underlying cause of which remains poorly understood. Here, by leveraging a model plasticized polymer electrolyte based on conventional succinonitrile plastic crystals, we uncover its failure origin in Na⁰batteries is associated with the formation of a thick and non‐uniform solid electrolyte interphase (SEI) and whiskery Na⁰nucleation/growth. Furthermore, we design a new additive‐embedded plasticized polymer electrolyte to manipulate the Na⁰deposition and SEI formulation. For the first time, we demonstrate that introducing fluoroethylene carbonate (FEC) additive into the succinonitrile‐plasticized polymer electrolyte can effectively protect Na⁰against interfacial corrosion by facilitating the growth of dome‐like Na⁰with thin, amorphous, and fluorine‐rich SEIs, thus enabling significantly improved performances of Na//Na symmetric cells (1,800 h at 0.5 mA cm⁻²) and Na//Na₃V₂(PO₄)₃full cells (93.0 % capacity retention after 1,200 cycles at 1 C rate in coin cells and 93.1 % capacity retention after 250 cycles at C/3 in pouch cells at room temperature). Our work provides valuable insights into the interfacial failure of plasticized polymer electrolytes and offers a promising solution to resolving the interfacial instability issue.

    

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4. A Sodium–Antimony–Telluride Intermetallic Allows Sodium‐Metal Cycling at 100% Depth of Discharge and as an Anode‐Free Metal Battery

   https://doi.org/10.1002/adma.202106005  

   Wang, Yixian ; Dong, Hui ; Katyal, Naman ; Hao, Hongchang ; Liu, Pengcheng ; Celio, Hugo ; Henkelman, Graeme ; Watt, John ; Mitlin, David ( November 2021 , Advanced Materials)

   Repeated cold rolling and folding is employed to fabricate a metallurgical composite of sodium–antimony–telluride Na₂(Sb_2/6Te_3/6Vac_1/6) dispersed in electrochemically active sodium metal, termed “NST‐Na.” This new intermetallic has a vacancy‐rich thermodynamically stable face‐centered‐cubic structure and enables state‐of‐the‐art electrochemical performance in widely employed carbonate and ether electrolytes. NST‐Na achieves 100% depth‐of‐discharge (DOD) in 1mNaPF₆in G2, with 15 mAh cm⁻²at 1 mA cm⁻²and Coulombic efficiency (CE) of 99.4%, for 1000 h of plating/stripping. Sodium‐metal batteries (SMBs) with NST‐Na and Na₃V₂(PO₄)₃ (NVP) or sulfur cathodes give significantly improved energy, cycling, and CE (>99%). An anode‐free battery with NST collector and NVP obtains 0.23% capacity decay per cycle. Imaging and tomography using conventional and cryogenic microscopy (Cryo‐EM) indicate that the sodium metal fills the open space inside the self‐supporting sodiophilic NST skeleton, resulting in dense (pore‐free and solid electrolyte interphase (SEI)‐free) metal deposits with flat surfaces. The baseline Na deposit consists of filament‐like dendrites and “dead metal”, intermixed with pores and SEI. Density functional theory calculations show that the uniqueness of NST lies in the thermodynamic stability of the Na atoms (rather than clusters) on its surface that leads to planar wetting, and in its own stability that prevents decomposition during cycling.

    

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5. A BF 3 ‐Doped MXene Dual‐Layer Interphase for a Reliable Lithium‐Metal Anode

   https://doi.org/10.1002/adma.202210111  

   Shang, Mingwei ; Shovon, Osman Goni ; Wong, Francis En Yoong ; Niu, Junjie ( December 2022 , Advanced Materials)

   A dual‐layer interphase that consists of an in‐situ‐formed lithium carboxylate organic layer and a thin BF₃‐doped monolayer Ti₃C₂MXene on Li metal is reported. The honeycomb‐structured organic layer increases the wetting of electrolyte, leading to a thin solid electrolyte interface (SEI). While the BF₃‐doped monolayer MXene provides abundant active sites for lithium homogeneous nucleation and growth, resulting in about 50% reduced thickness of inorganic‐rich components among the SEI layer. A low overpotential of less than 30 mV over 1000 h cycling in symmetric cells is received. The functional BF₃ groups, along with the excellent electronic conductivity and smooth surface of the MXene, greatly reduce the lithium plating/stripping energy barrier, enabling a dendrite‐free lithium‐metal anode. The battery with this dual‐layer coated lithium metal as the anode displays greatly improved electrochemical performance. A high capacity‐retention of 175.4 mAh g⁻¹at 1.0 C is achieved after 350 cycles. In a pouch cell with a capacity of 475 mAh, the battery still exhibits a high discharge capacity of 165.6 mAh g⁻¹with a capacity retention of 90.2% after 200 cycles. In contrast to the fast capacity decay of pure Li metal, the battery using NCA as the cathode also displays excellent capacity retention in both coin and pouch cells. The dual‐layer modified surface provides an effective approach in stabilizing the Li‐metal anode.

    

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