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Abstract A new concentrated ternary salt ether‐based electrolyte enables stable cycling of lithium metal battery (LMB) cells with high‐mass‐loading (13.8 mg cm−2, 2.5 mAh cm−2) NMC622 (LiNi0.6Co0.2Mn0.2O2) cathodes and 50 μm Li anodes. Termed “CETHER‐3,” this electrolyte is based on LiTFSI, LiDFOB, and LiBF4with 5 vol% fluorinated ethylene carbonate in 1,2‐dimethoxyethane. Commercial carbonate and state‐of‐the‐art binary salt ether electrolytes were also tested as baselines. With CETHER‐3, the electrochemical performance of the full‐cell battery is among the most favorably reported in terms of high‐voltage cycling stability. For example, LiNixMnyCo1–x–yO2(NMC)‐Li metal cells retain 80% capacity at 430 cycles with a 4.4 V cut‐off and 83% capacity at 100 cycles with a 4.5 V cut‐off (charge at C/5, discharge at C/2). According to simulation by density functional theory and molecular dynamics, this favorable performance is an outcome of enhanced coordination between Li+and the solvent/salt molecules. Combining advanced microscopy (high‐resolution transmission electron microscopy, scanning electron microscopy) and surface science (X‐ray photoelectron spectroscopy, time‐of‐fight secondary ion mass spectroscopy, Fourier‐transform infrared spectroscopy, Raman spectroscopy), it is demonstrated that a thinner and more stable cathode electrolyte interphase (CEI) and solid electrolyte interphase (SEI) are formed. The CEI is rich in lithium sulfide (Li2SO3), while the SEI is rich in Li3N and LiF. During cycling, the CEI/SEI suppresses both the deleterious transformation of the cathode R‐3m layered near‐surface structure into disordered rock salt and the growth of lithium metal dendrites.
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This content will become publicly available on December 23, 2025
Understanding Cathode–Electrolyte Interphase Formation in Solid State Li‐Ion Batteries via 4D‐STEM
Abstract Interphase layers that form at contact points between the solid electrolyte (SE) and cathode active material in solid‐state lithium‐ion batteries (SS‐LIBs) increase cell impedance, but the mechanisms for this interphase formation are poorly understood. Here, we demonstrate a simple workflow to study cathode–electrolyte interphase (CEI) formation using 4D‐scanning transmission electron microscopy (4D‐STEM) that does not require SS‐LIB assembly. We show benefits of MoCl5:EtOH as a chemical delithiating agent, and prepare chemically delithiated cathode LiNi0.6Co0.2Mn0.2O2(NMC) powder in contact with Li10GeP2S12(LGPS) SE powder as a SS‐LIB CEI surrogate. We map the composition and structure of the CEI layers using 4D‐STEM, energy dispersive X‐ray spectroscopy (EDS), and electron pair distribution function analysis (ePDF). EDS indicates O migration from NMC into LGPS. ePDF analysis indicates sulfate and phosphate formation localized on the surface of LGPS, as well as Li2O formation within the LGPS phase, and self‐decomposition of NMC. These results are consistent with an electrochemical self‐discharge mechanism for interphase formation arising from coupled redox reactions of sulfur oxidation in LGPS and transition metal reduction in NMC. This suggests that coatings which stop anion transport but allow Li+and e−transport may prevent interphase formation and reduce impedance in SS‐LIBs.
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- PAR ID:
- 10641603
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 15
- Issue:
- 11
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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