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Abstract The glassy solid electrolyte Lithium phosphorous oxynitride (LiPON) has been widely researched in thin film solid state battery format due to its outstanding stability when cycled against lithium. In addition, recent reports show thin film LiPON having interesting mechanical behaviors, especially its ability to resist micro‐scale cracking via densification and shear flow. In the present study, we have produced bulk LiPON glasses with varying nitrogen contents by ammonolysis of LiPO₃melts. The resulting compositions were determined to be LiPO_3‐3z/2N_z, where 0 ≤ z ≤ 0.75, and the z value of 0.75 is among the highest ever reported for this series of LiPON glasses. The short‐range order structures of the different resulting compositions were characterized by infrared, Raman,³¹P magic angle spinning nuclear magnetic resonance, and X‐ray photoelectron spectroscopies. Instrumented nano‐indentation was used to measure mechanical properties. It was observed that similar to previous studies, both trigonally coordinated (N_t) and doubly bonded (N_d) N co‐exist in the glasses in about the same amounts forz ≤ 0.36, the limit of N content in most previous studies. For glasses withz > 0.36, it was found that the fraction of the N_tincreased significantly while the fraction of N_dcorrespondingly decreased. The incorporation of nitrogen increased both the elastic modulus and hardness of the glass by approximately a factor of 1.5 when N/P ratio reaches 0.75. At the same time, an apparent embrittlement of the glass was observed due to nitridation, which was revealed by nanoindentation with an extra sharp nanoindenter tip. 

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. 

Oxygen doping reduces free volume yet paradoxically enhances amorphous framework flexibility, facilitating Na⁺ion diffusion. This balance leads to an initial increase, then a decline, observed in conductivity of NaPSO electrolytes. 

In the development of sodium all-solid-state batteries (ASSBs), research efforts have focused on synthesizing highly conducting and electrochemically stable solid-state electrolytes. Glassy solid electrolytes (GSEs) have been considered very promising due to their tunable chemistry and resistance to dendrite growth. For these reasons, we focus here on the atomic-level structures and properties of GSEs in the compositional series (0.6–0.08y)Na2S + (0.4 + 0.08y)[(1 – y)[(1 – x)SiS2 + xPS5/2] + yNaPO3] (NaPSiSO). The mechanical moduli, glass transition temperatures, and temperature-dependent conductivity were determined and related to their short-range order structures that were determined using Raman, Fourier transform infrared, and 31P and 29Si magic angle spinning nuclear magnetic resonance spectroscopies. In addition, the conductivity activation energies were modeled using the Christensen–Martin–Anderson–Stuart model. These GSEs appear to be highly crystallization-resistant in the supercooled liquid region where no measurable crystallization below 450 °C could be observed in differential scanning calorimetry studies. Additionally, these GSEs were found to be highly conducting, with conductivities on the order of 10–5 (Ω cm)−1 at room temperature, and processable in the supercooled state without crystallization. For all these reasons, these NaPSiSO GSEs are considered to be highly competitive and easily processable candidate GSEs for enabling sodium ASSBs. 

Sulfide-based solid electrolytes (SEs) are emerging as compelling materials for all-solid-state batteries (ASSBs), primarily due to their high ionic conductivities and robust mechanical stability. In particular, glassy SEs (GSEs) comprising mixed Si and P glassformers show promise, thanks to their efficient synthesis process and their intrinsic ability to prevent lithium dendrite growth. However, to date the complexity of their glassy structures hinders a complete understanding of the relationships between their structures and properties. Here, new machine learning force field (ML- FF) specifically designed for lithium sulfide-based GSEs has been developed. This ML-FF has been used to investigate the structural characteristics, mechanical properties, and lithium ionic conductivities in binary lithium thiosilicate and lithium thiophosphate GSEs, as well as their ternary mixed glassformer (MGF) lithium thiosilicophosphate GSEs. Molecular dynamic (MD) simulations using the ML-FF were conducted to explore the glass structures in varying compositions, including binary Li2S-SiS2 and Li2S-P2S5, as well as ternary Li2S-SiS2-P2S5. The simulations with the ML-FF yielded consistent results in terms of density, elastic modulus, radial distribution functions, and neutron structure factors, compared to DFT and experimental work. A key focus of this study was to investigate the local environments of Si and P molecular clusters. We discovered that most Si atoms in the Li2S-SiS2 GSE are situated in an edge-sharing environment, while the Li2S-P2S5 glass contained a minor proportion of edge-sharing P2S62- environments. In the ternary 60Li2S-32SiS2-8P2S5 glass, the ML-FF predicted similar P environments as observed in the binary Li2S-P2S5 glass. Additionally, it indicated the coexistence of corner and edge-sharing between PS4 and SiS4 tetrahedra in this ternary composition. Concerning lithium ionic conductivity at 300K, all studied glass compositions exhibited similar magnitudes and followed the Arrhenius relationship. The 50Li2S-50SiS2 glass displayed the lowest conductivity at 2.1 mS/cm, while the 75Li2S-25P2S5 composition exhibited the highest at 3.6 2 mS/cm. The ternary glass showed a conductivity of 2.57 mS/cm, sitting between the two. Interestingly, the predicted conductivities were about an order of magnitude higher than experimental values for the binary glasses but aligning more closely with that of the ternary glass. Moreover, an in-depth analysis of lithium-ion diffusion over the MD trajectory in the ternary glass demonstrated a significant correlation between diffusion pathways and the rotational dynamics of nearby SiS4 or PS4 tetrahedra. The ML-FF developed in this study shows immense potential as a versatile tool for exploring a broad spectrum of solid-state and mixed-former sulfide-based electrolytes. 

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. 

In this work, the compositional series of sulfide and mixed oxysulfide (MOS) glasses 0.56Li2S + 0.44[(0.33-x)PS5/2 + xPO5/2 + 0.67SiS2] was prepared, where 0 ≤ x ≤ 0.33, and their short range order (SRO) structures and their thermal properties have been investigated. Powder x-ray diffraction (XRD) confirmed that the MOS glasses were free from crystallization, with only very minor diffraction peaks in the x = 0 glass being observed. Fourier transform infrared (FT-IR), Raman, and 29Si and 31P magic angle spinning (MAS) NMR spectroscopies were used to identify the SRO structures present in these glasses. These spectra revealed oxygen migration from P to Si during synthesis. Although oxygen was introduced in the form of phosphorus oxide, the majority of the oxygen in these glasses ends up being bonded to silicon, thereby creating sulfur-rich SROs centered by phosphorus and MOS SROs centered by silicon. It was further found that the P-S SRO species were predominantly charged non-bridging sulfurs (NBS). The Si SRO species were comprised of neutral bridging oxygens (BOs) and charged non-bridging oxygens (NBOs) and neutral bridging sulfurs (BS) and charged non-bridging sulfurs with the neutral BO and BS species being larger in fraction than the NBO and NBS. These results suggest that the preponderance of the mobile Li+ cations in these glasses are located near the more negatively charged P centers and not near the more neutrally charged Si centers. The average negative charge of the P SRO structures was found to be ∼ − 3.0 with ∼97% of the phosphorous species in the P0 SRO while the average negative charge of the Si SRO structures was found to be −2.3. Consistent with the creation of the large numbers of NBS on the P and more BOs and BSs on the Si, these values are more negative and more positive, respectively, than the compositionally expected average value of −2.55. Differential scanning calorimetry (DSC) measurements of their glass transition (Tg) and crystallization (Tc) temperatures showed that the Tgs of these glasses are higher than 300 °C and their working ranges, ΔT ≡ Tc – Tg, are ∼100 °C. 

Na4P2S7-6xO4.62xN0.92x (NaPSON) glassy solid electrolytes (GSEs) were prepared and tested for their electrochemical properties and processability into thin films. The x = 0.2 composition (NaPSON-2) was found to be highly conducting, non-crystallizable, largely stable against Na-metal and supports symmetric cell cycling up to >100 µA cm-2 without shorting and for these reasons was processed into thin films drawn to 50 m and tested in symmetric and asymmetric cells. Measurements of the sodium ion conductivity using symmetric cells demonstrated that the conductivity of NaPSON-2 was unchanged by film forming. Galvanostatic cycling at 5 A cm-2 of 1.3 mm NaPSON-2 showed stability over 450 hours, while cycling a 50 m thin film showed a very slow growth in the resistance. Cyclic voltammetry and x-ray photoelectron spectroscopy of the NaPSON-2 thin film GSE revealed that it did not react with Na-metal at its surface, but rather in the bulk of the film, showing S, Na2S, and Na3P reaction products. The source of the surface stability was determined to be the preferential segregation of trigonally coordinated nitrogen. These low-cost and easily processed NaPSON GSEs provide a system of materials which could provide for significantly lower cost higher energy density grid-scale batteries. 

In this work we demonstrate that cell pressure controls the morphology and stability of electroplated sodium metal deposits on carbon black nucleation layers in ether-based electrolytes. At pressures below 500 kPa we observe the presence of three-dimensional Na nuclei accompanied by low Coulombic efficiencies (CEs less than 98%). Conversely, at pressures between 500 and 1272 kPa we observe smooth, planar Na deposits, high CEs up to 99.9%, and stable electrochemical cycling. Through a series of tests conducted at elevated current densities and with or without rest stages, our findings elucidate the balance of important competing time scales for creep and morphology evolution under pressure and the rate of charge transfer that determines Na morphology and stability. This highlights how chemo-mechanical effects at pressure ranges relevant for battery packaging in coin and pouch cells are key factors in the design and operation of Na metal batteries. 

Here we provide an in-depth structural characterization of the amorphous ionic glasses LiPON and LiSiPON with high Li content. Based on ab-initio molecular dynamics simulations, the structure of these materials is an inverted structure with either isolated polyanion tetrahedra or polyanion dimers suspended in a Li+ matrix. Based on neutron scattering data, this type of inverted structure leads to a significant amount of medium-range ordering in the structure, as demonstrated by two sharp diffraction peaks and a periodic structural oscillation in the density function G(r). On a local scale, adding N and Si increases the number of anion bridges and polyanion dimer structures, leading to higher ionic conductivity. In the medium range ordering, the addition of Si leads to more disorder in the polyanion substructure but a significant increase in the ordering of the O substructure. Finally, we demonstrate that this inverted structure with medium range ordering results in a glassy material that is both mechanically stiff and ductile on the nanoscale.