Editors⇔ choice⇔mechanistic elucidation of anion intercalation into graphite from binary-mixed highly concentrated electrolytes via complementary 19F MAS NMR and XRD studies

Lukas Haneke, Joop Enno Frerichs, Andreas Heckmann, Michael M. Lerner, Taner Akbay, Tatsumi Ishihara, Michael Ryan Hansen, Martin Winter, Tobias Placke

    Research output: Contribution to journalReview articlepeer-review

    8 Citations (Scopus)

    Abstract

    Dual-graphite batteries have emerged as promising candidate for sustainable energy storage due to their potentially low costs and absence of toxic materials. However, the mechanism of anion intercalation and the structures of the resulting graphite intercalation compounds (GICs) are still not well understood. Here, we systematically evaluate the anion intercalation characteristics into graphite for three highly concentrated electrolytes containing LiPF6, LiTFSI and their equimolar binary mixture. The binary mixture exhibits a significantly enhanced capacity retention and improved intercalation kinetics compared to the single-salt electrolytes in graphite ∣∣ Li metal cells. In situ X-ray diffraction studies prove the formation of stage 1-GICs and a homogeneous distribution of anions within graphite. From ex situ solid-state 19F magic-angle spinning (MAS) nuclear magnetic resonance (NMR) measurements, GICs can be identified at various states-of-charge (SOCs). The 19F chemical shifts of intercalated anions indicate no significant charge transfer between anion and graphite. The observed narrow 19F linewidths of the GIC-signals are most likely caused by a high translational and/or rotational mobility of the intercalates. Furthermore, the 19F MAS NMR studies allow the identification of the molar ratios for PF6 and TFSI anions intercalated into graphite, suggesting a preferred intercalation of PF6 anions, especially at lower SOCs.

    Original languageEnglish
    Article number140526
    JournalJournal of the Electrochemical Society
    Volume167
    Issue number14
    DOIs
    Publication statusPublished - Nov 2020

    All Science Journal Classification (ASJC) codes

    • Electronic, Optical and Magnetic Materials
    • Renewable Energy, Sustainability and the Environment
    • Surfaces, Coatings and Films
    • Electrochemistry
    • Materials Chemistry

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