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Abstract 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. 

Abstract This is the first report of molybdenum carbide‐based electrocatalyst for sulfur‐based sodium‐metal batteries. MoC/Mo₂C is in situ grown on nitrogen‐doped carbon nanotubes in parallel with formation of extensive nanoporosity. Sulfur impregnation (50 wt% S) results in unique triphasic architecture termed molybdenum carbide–porous carbon nanotubes host (MoC/Mo₂C@PCNT–S). Quasi‐solid‐state phase transformation to Na₂S is promoted in carbonate electrolyte, with in situ time‐resolved Raman, X‐ray photoelectron spectroscopy, and optical analyses demonstrating minimal soluble polysulfides. MoC/Mo₂C@PCNT–S cathodes deliver among the most promising rate performance characteristics in the literature, achieving 987 mAh g⁻¹at 1 A g⁻¹, 818 mAh g⁻¹at 3 A g⁻¹, and 621 mAh g⁻¹at 5 A g⁻¹. The cells deliver superior cycling stability, retaining 650 mAh g⁻¹after 1000 cycles at 1.5 A g⁻¹, corresponding to 0.028% capacity decay per cycle. High mass loading cathodes (64 wt% S, 12.7 mg cm⁻²) also show cycling stability. Density functional theory demonstrates that formation energy of Na₂S_x(1 ≤x ≤ 4) on surface of MoC/Mo₂C is significantly lowered compared to analogous redox in liquid. Strong binding of Na₂S_x(1 ≤x ≤ 4) on MoC/Mo₂C surfaces results from charge transfer between the sulfur and Mo sites on carbides’ surface.