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Abstract The preparation of 0.58 Li₂S + 0.315 SiS₂+ 0.105 LiPO₃glass, and the impacts of polysulfide and P^1Pdefect structure impurities on the glass transition temperature (T_g), crystallization temperature (T_c), working range (ΔT≡ T_c‐ T_g), fragility index, and the Raman spectra were evaluated using statistical analysis. In this study, 33 samples of this glass composition were synthesized through melt‐quenching. Thermal analysis was conducted to determine the glass transition temperature, crystallization temperature, working range, and fragility index through differential scanning calorimetry. The quantity of the impurities described above was determined through Raman spectroscopy peak analysis. Elemental sulfur was doped into a glass to quantify the wt% sulfur content in the glasses. Linear regression analysis was conducted to determine the impact of polysulfide impurities and P^1Pdefect impurities on the thermal properties. Polysulfide impurities were found to decrease theT_gat rate of nearly 12°C per 1 wt% increase in sulfur concentration. The sulfur concentration does not have a statistically significant impact on the other properties (α = 0.05). The P^1Pdefect structure appears to decrease the resistance to crystallization of the glass by measurably decreasing the working range of the glasses, but further study is necessary to fully quantify and determine this. 

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. 

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. 

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. 

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. 

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. 

Glassy solid-state electrolytes present several advantages over other classes of solid-state electrolytes, but some material and design challenges must be overcome prior to commercialization. 

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.