Lithium Thiosilicophosphate Glassy Solid Electrolytes Synthesized by High-Energy Ball-Milling and Melt-Quenching: Improved Suppression of Lithium Dendrite Growth by Si Doping

Abstract

Due to the volatility of P2S5, the ambient pressure synthesis of Li2S + P2S5 (LPS) has been limited to planetary ball-milling (PBM). To utilize PBM of LPS to generate a solid electrolyte (SE), the as-synthesized powder sample must be pressed into pellets, and as such the presence of as-pressed grain boundaries in the SE cannot be avoided. To eliminate the grain boundaries, LPS doped with SiS2 has been studied because SiS2 lowers the vapor pressure of the melt and promotes strong glass formation, which in combination allows for greater ease in synthesis. In this work, we have examined the structures and electrochemical properties of lithium thiosilicophosphate 0.6Li2S + 0.4­[xSiS2 + 1.5­(1 – x)­PS5/2], 0 ≤ x ≤ 1, glassy solid electrolytes (GSEs) prepared by both PBM and melt-quenching (MQ). It is shown that the critical current density improved after incorporating SiS2, reaching 1.5 mA/cm2 for the x = 0.8 composition. However, the interfacial reaction of MQ GSE with lithium metal introduced microcracks, which shows that further research is needed to explore and develop more stable GSE compositions. These fundamental results can help to understand the interface reaction and formation and as such can provide a guide to design improved homogeneous GSEs with SiS2 as a glass former, which have no grain boundaries and thereby may help suppress lithium dendrite formation.

New Amorphous Oxy-Sulfide Solid Electrolyte Material: Anion Exchange, Electrochemical Properties, and Lithium Dendrite Suppression via In Situ Interfacial Modification

“…This suggests that the decomposition of (presumably) more weakly bonded Si–S SRO units in MGF MOS GSSEs occurred during the PBM mixing and glass formation processes. We have seen this and reported on this behavior in pure sulfide Li–Si–P–S PBM GSSEs . In general, after ball-milling for 20 h, the GSSE contains Si–O, Si–S, P–O, and P–S units and cubic silicon according to the above Raman analysis.…”

“…It should be noted that the exact value for the CCD depends on the experimental setup. We used a step-increased measurement, which contains only one cycle and 1 h for each current density in our previous work . However, it was shown in our previous work that the number of cycles also influences the CCD value observed for a particular GSSE.…”

Emerging Role of Non-crystalline Electrolytes in Solid-State Battery Research

“…A positive correlation between increases in the ionic diffusion pathway volume and values of ionic conductivity are well-documented for crystalline electrolytes as well (Bachman et al, 2015). The practical advantages of Si or O doping on the performance of LPS is shown in Figures 5C,D, where an increase in stability at high current density is observed when the electrolyte composition is changed from 0.6Li 2 S + 0.4P 2 S 5 to 0.6Li 2 S + 0.4[0.4SiS 2 + 0.9P 2 S 5 ], respectively (Zhao et al, 2020).…”

Sulfide glass solid-state electrolyte separators for Li metal batteries: using an interlayer to increase rate performance and reduce stack pressure

“…Using this method small ingots of approximately 5 mm diameter were obtained. The second method was used to synthesize glass compositions with high melt volatility; namely, (Li 2 S) 60 (SiS 2 ) x (P 2 S 5 ) 40Àx (x = 0, 4, 20), (Li 2 S) 70 (P 2 S 5 ) 30 and (Li 2 S) 75 (P 2 S 5 ) 25 . SSEs with composition (Li 2 S) 60 (SiS 2 ) x (P 2 S 5 ) 40Àx (x = 8, 12, 16) were also synthesized by the second melt quenching method, but had poor glass formability.…”

“…29,30 Generally, the vibrational modes below 200 cm À1 and around 450 cm À1 are attributable to sulfur species, 31 while the vibrational modes in the 350-450 cm À1 range are attributable to solvated glass structural units (P 2 S 6 ) 4À , (P 2 S 7 ) 4À , and (PS 4 ) 3À . 25,26 A vibrational mode of DME, centered at 365 cm À1 , is minorly convolved with the structural units' vibrational modes, but does not impact analyses. Since several unidentified vibrational modes are observed in the 220-330 cm À1 range, our analysis therefore focuses on the range of 330-520 cm À1 .…”