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We present a 23Na nuclear spin dynamics model for interpreting nuclear magnetic resonance (NMR) spin-lattice relaxation and central linewidth data in the invert glass system Na4P2S7-xOx, 0 ≤ x ≤ 7. The glassy nature of this material results in variations in local Na+ cation environments that may be described by a Gaussian distribution of activation energies. A consistent difference between the mean activation energies determined by NMR and DC conductivity measurements was observed, and interpreted using a percolation theory model. From this, the Nasingle bondNa coordination number in the sodium cation sublattice was obtained. These values were consistent with jumps through tetrahedral faces of the sodium cages for the sulfur rich glasses, x < 5, consistent with proposed models of their short range order (SRO) structures. From NMR spin-echo measurements, we determined the Nasingle bondNa second moment M2 resulting from the Nasingle bondNa magnetic dipole interaction of nearest neighbors. Values of M2 obtained as a function of sodium number density N were in agreement with models for uniform sodium distribution, indicating that these invert glass systems form so as to maximize the average Nasingle bondNa distance. A simple Coulombic attraction model between Na+ cation and X (=S−, O−) anion was applied to calculate the activation energy. In the range 1.5 ≤ x ≤ 7, an increase in activation energy with increasing oxygen content x occurred, and was consistent with the decrease in average anionic radius, and the increase in Coulombic attraction. For small oxygen additions, 0 ≤ x ≤ 1.5, the suggested minimum at low oxygen concentration seen in the activation energies obtained from DC conductivity data is not evident in the model. 

Abstract All-solid-state sodium batteries (ASSSBs) are promising candidates for grid-scale energy storage. However, there are no commercialized ASSSBs yet, in part due to the lack of a low-cost, simple-to-fabricate solid electrolyte (SE) with electrochemical stability towards Na metal. In this work, we report a family of oxysulfide glass SEs (Na 3 PS 4− x O x , where 0 <  x  ≤ 0.60) that not only exhibit the highest critical current density among all Na-ion conducting sulfide-based SEs, but also enable high-performance ambient-temperature sodium-sulfur batteries. By forming bridging oxygen units, the Na 3 PS 4− x O x SEs undergo pressure-induced sintering at room temperature, resulting in a fully homogeneous glass structure with robust mechanical properties. Furthermore, the self-passivating solid electrolyte interphase at the Na|SE interface is critical for interface stabilization and reversible Na plating and stripping. The new structural and compositional design strategies presented here provide a new paradigm in the development of safe, low-cost, energy-dense, and long-lifetime ASSSBs. 

Abstract While much of the current research on glassy solid electrolytes (GSEs) has focused on the binary Li₂S+P₂S₅system, compositions with Si are of interest because Si promotes stronger glass formation and allows low‐cost melt‐quenching (MQ) synthesis under ambient pressure. Another advantage is that they can be formed in homogeneous and continuous glass forms, as a result they are free of grain boundaries. In this work, we have examined the structures and electrochemical properties of bulk glass pieces of sulfide and oxy‐sulfide GSE compositions and have also expanded the study by using LiPON glass as a dopant to produce an entirely new class of nitrogen doped mixed oxy‐sulfide nitride (MOSN) GSEs. Upon doping with oxygen and nitrogen, the solid electrolyte interface (SEI) is stabilized and the doped MOSN GSE exhibits a critical current density (CCD) of 1.8 mA cm⁻²at 100 °C. We also report on improving the glass quality, the SEI engineering and its limitations, and future plans of improving the electrochemical performance of these homogeneous MQ MOSN GSEs. These fundamental results can help to understand the structures and doping effects of the bulk GSEs, and as such can provide a guide to design improved homogeneous grain‐boundary‐free GSEs.