NaPON Doping of Na₄P₂S₇ Glass and Its Effects on the Structure and Properties of Mixed Oxy-Sulfide-Nitride Phosphate Glass

Abstract

The preparation, properties, and short-range order (SRO) structures of glasses in the series (1–x)[2/3Na2S + 1/3P2S5] + x[1/3Na2S + 2/3NaPO2.31N0.46] = Na4P2S7–6x O4.62x N0.92x , where 0 ≤ x ≤ 0.5 (NaPSON), are reported on. In this study, these mixed oxy-sulfide-nitride (MOSN) glasses were prepared by adding the nitrided material NaPO3‑(3/2)y N y ; y = 0.46 = NaPO2.31N0.46 (NaPON) to the base sulfide glass Na4P2S7. For comparison purposes, additions of the unitrided material, y = 0, NaPO3, were also studied (NaPSO). Accordingly, large batches of bubble-free glass could be prepared making this route of nitrogen doping amendable toward scaling-up the glass melting process; though, only small amounts of nitrogen could be incorporated in this manner. Nitrogen and sulfur compositional analysis were combined with XPS, Raman, FT-IR, and 31P MAS NMR spectroscopies to determine the amount of retained nitrogen in the glass after melting and quenching and to determine the effect of the added nitrogen and oxygen on the structure of the base pure sulfide glass Na4P2S7, x = 0.0. The nitrogen content increased linearly with the addition of NaPON, but was found, through quantitative 31P MAS NMR analysis, to be approximately half that expected at each value of x. Despite the small amount of nitrogen retained in these glasses, profound increases in the glass transition (T g) and crystallization temperatures (T c) were found with increasing x. For the intermediate values of x, 0.2 and 0.3, no crystallization of the supercooled melt was observed even 250 °C above the T g. It was found that the addition of NaPON to the series caused a disproportionation reaction, where the oxide and oxy-nitride SRO species preferentially formed covalent, networking phosphate chains, forcing the sodium modifier to ionic sulfide units with large fractions of nonbridging sulfurs (NBSs). This disproportionation reaction was also observed in the NaPO3 doped series of glasses, but to a smaller extent. Oxygen was found in both bridging oxygen (BO) and nonbridging oxygen (NBOs) structures while the sulfur was predominantly found in nonbridging sulfur (NBS) structures. N 1s XPS and 31P NMR studies provided insight into the nitrogen bearing phosphorus units and the wt % of nitrogen that was retained in the quenched glasses. It was found that trigonally coordinated nitrogen (Nt) was preferentially retained in the melt, whereas it is proposed that the linearly coordinated (doubly bonded) nitrogen (Nd) accounts for the lost nitrogen in the glasses.

Effects of LiPON Incorporation on the Structures and Properties of Mixed Oxy-Sulfide-Nitride Glassy Solid Electrolytes

“…In the lower wavenumber range, four separate absorbance modes are identified inside the first broad absorption envelop located from 500 to 650 cm –1 . The first mode from 540 to 570 cm –1 is assigned to the δ­(Si–S–Si) of SiS 2 and the non-bridging sulfur (NBS) of PS 4 3– , the next mode from 580 to 590 cm –1 is assigned to the δ­(Si–O–Si) bending mode, and the mode situated at 610–630 cm –1 is assigned to the ν as (PS 3 – ) stretch of the P 2 S 6 2– species. ,,− The second main broad envelope in this region is located between 650 and 800 cm –1 , two absorbance modes can be made out with both modes corresponding to the NBS Si–S – of the SiS 6 4– species from 639 to 684 cm –1 and the NBS, PS, of PSO 3 3– anions from 709 to 733 cm –1 . , …”

Optimized Thin Film Processing of Sodium Mixed Oxy-Sulfide-Nitride Glassy Solid Electrolytes for All-Solid-State Batteries

“…The Raman and FT-IR spectra of NaPSON-2 were used to determine if there were any significant chemical or structural changes in the GSE during thin film processing, Figure . These spectra have already been used to carefully probe the SRO species in these NaPSO and NaPSON GSEs in bulk form and as such provided deep insight into the kind and proportion of each SRO species in these GSEs. , The main peak in the Raman spectra centered at 400 cm –1 is attributed to the P 2 S 7 4– SRO unit, which has two shoulders at 387 and 415 cm –1 , attributed to the P 2 S 6 4– and PS 4 3– SRO units, respectively. , The peaks between 450 and 550 cm –1 arise from vibrational modes associated with an impurity level of ionic, Na + − S­( S n )­S – Na + , and covalent, S n , sulfur species. , The FT-IR spectra shows the same pure sulfide SRO species as seen in the Raman spectra, where peaks centered at 560 and 610 cm –1 are attributed to the non-bridging sulfur (NBS) of the PS 4 3– and P 2 S 7 4– anions, respectively . The FT-IR spectra also show a mode centered at 463 cm –1 , which is attributed to the dihedral bending of the bridging sulfur (BS), P–S–P, bonds and the asymmetric stretch of ionic sulfur, – S–(S n )­S – . , The modes centered at 878 and 1043 cm –1 are attributed to the asymmetric vibration of bridging oxygens (BOs), P–O–P, bonds and the symmetric stretch of P 2 O 7 4– anions .…”

“…These spectra have already been used to carefully probe the SRO species in these NaPSO and NaPSON GSEs in bulk form and as such provided deep insight into the kind and proportion of each SRO species in these GSEs. 30,43 The main peak in the Raman spectra centered at 400 cm −1 is attributed to the P 2 S 7 4− SRO unit, which has two shoulders at 387 and 415 cm −1 , attributed to the P 2 S 6 4− and PS 4 3− SRO units, respectively. 44,45 The peaks between 450 and 550 cm −1 arise from vibrational modes associated with an impurity level of ionic, Na + − S(S n )-S − Na + , and covalent, S n , sulfur species.…”

“…3− anions, which form in the glass as a result of a disproportionation reaction, 30 leading to instability issues. Thus, while the S/O ratio is important, engineering the structural units present in GSEs is the key in improving stability.…”

“…These MOSN GSEs have the full composition (1- x )­[2Na 2 S + P 2 S 5 ] + x [Na 2 S + 2NaPO 2.31 N 0.46 ], which is equivalent to Na 4 P 2 S 7–6 x O 4.62 x N 0.92 x , where 0 ≤ x ≤ 0.5 (NaPSON). With the atomic level short-range order (SRO) structures and their thermal behaviors already reported, these NaPSON GSEs were synthesized in order to explore an optimized and processable composition ( x in the expression above) that meets the required metrics of SSEs compatible with Na-metal anodes. Although the conductivities of these MOSN GSEs are very good for sodium ion conducting GSEs, they are still relatively modest and in the range of 1 × 10 –6 (Ω cm) −1 at room temperature, but these NaPSON GSEs exhibit excellent chemical and thermal stability enabling processing into thin films (10s μm) without any evidence of crystallization or phase separation.…”