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Hybrid sulfide-polymer composite electrolytes are promising candidates to enable lithium metal batteries because of their high ionic conductivity and flexibility. These composite materials are primarily prepared through solution casting methods to obtain a homogenous distribution of polymer within the inorganic. However, little is known about the influence of the morphology of the polymer and the inorganic on the ionic conductivity and electrochemical behavior of these hybrid systems. In this study, we assess the impact of processing methodology, either solution processing or solvent-free ball milling, on overall performance of hybrid electrolytes containing amorphous Li3PS4(LPS) and non-reactive polyethylene (PE). We demonstrate that using even non-polar, non-reactive solvents can alter the LPS crystalline structure, leading to a lower ionic conductivity. Additionally, we show that ball milling leads to a non-homogenous distribution of polymer within the inorganic, which leads to a higher ionic conductivity than samples processed via solution casting. Our work demonstrates that the morphology of the polymer and the sulfide plays a key role in the ionic conductivity and subsequent electrochemical stability of these hybrid electrolytes.
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Importance of multimodal characterization and influence of residual Li 2 S impurity in amorphous Li 3 PS 4 inorganic electrolytes
Amorphous Li 3 PS 4 (LPS) solid-state electrolytes are promising for energy-dense lithium metal batteries. LPS glass, synthesized from a 3 : 1 mol ratio of Li 2 S and P 2 S 5 , has high ionic conductivity and can be synthesized by ball milling or solution processing. Ball milling has been attractive because it provides the easiest route to access amorphous LPS with a conductivity of 3.5 × 10 −4 S cm −1 (20 °C). However, achieving the complete reaction of precursors via ball milling can be difficult, and most literature reports use X-ray diffraction (XRD) or Raman spectroscopy to confirm sample purity, both of which have limitations. Furthermore, the effect of residual precursors on ionic conductivity and lithium metal cycling is unknown. In this work, we illustrate the importance of multimodal characterization to determine LPS phase and chemical purity. To determine the residual Li 2 S content in LPS, we show that (1) XRD and 31 P solid state nuclear magnetic resonance (ssNMR) are insufficient and (2) Raman loses sensitivity at concentrations below 12 mol% Li 2 S. Most importantly, we show that 7 Li ssNMR is highly sensitive. Using 7 Li ssNMR, we investigate the effect of ball milling parameters and develop a robust and highly reproducible procedure for pure LPS synthesis. We find that as the residual Li 2 S precursor content increases, LPS conductivity decreases and lithium metal batteries exhibit higher overpotentials and poor cycle life. Our work reveals the importance of multimodal characterization techniques for amorphous solid-state electrolyte characterization and will enable better synthetic strategies for highly conductive electrolytes for efficient energy-dense solid-state lithium metal batteries.
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- Award ID(s):
- 2011854
- PAR ID:
- 10313828
- Date Published:
- Journal Name:
- Journal of Materials Chemistry A
- Volume:
- 9
- Issue:
- 35
- ISSN:
- 2050-7488
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1ta02754a
