Julian Baumgärtner


Last Name

Baumgärtner

First Name

Julian

ORCID

0000-0003-3287-0775

Organisational unit

03934 - Kovalenko, Maksym / Kovalenko, Maksym

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2022 - 20265
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Publications 1 - 5 of 5
  • On the Feasibility of Pairing Pyrochlore Iron(III) Hydroxy Fluoride Cathode with Argyrodite Li₆PS₅Cl Solid-State Electrolyte for Low-Cost All-Solid-State Batteries
    Item type: Journal Article
    Sivavec, Jaka; Baumgärtner, Julian; Stoian, Dragos C.; et al. (2025)
    Batteries & Supercaps
    As demand for low-cost, high-energy-density all-solid-state batteries continues to rise, exploring novel cathodes composed of earth-abundant elements is imperative. Iron hydroxy fluorides with the pyrochlore structure (Pyr-IHF) emerge as compelling cathode materials due to abundant natural reserves of their constituent elements, high energy density, and rate capability. In this work, we explore the viability of Pyr-IHF as a cathode material in all-solid-state batteries when paired with argyrodite-type Li₆PS₅Cl (LPSCl) solid-state electrolyte. Our findings show that the Pyr-IHF/LPSCl cathode delivers a high initial charge capacity of 172 mAh g⁻¹ at a 0.1 C rate, with ca. 65 % capacity retention after 50 cycles. Advanced characterization techniques, including focused ion beam-scanning electron microscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, and X-ray absorption spectroscopy, indicate a pronounced redox reaction between Pyr-IHF and LPSCl upon cell preparation, resulting in significant capacity contributions from the sulfur redox of LPSCl decomposition products during electrochemical cycling.
  • Single-Phase Lithiation in Iron Hydroxy Fluorides with Pyrochlore Structure
    Item type: Journal Article
    Baumgärtner, Julian; Stoian, Dragos C.; Marshall, Kenneth P.; et al. (2025)
    ACS Energy Letters
    3D transition metal fluorides have long been recognized as appealing low-cost, high-energy-density cathode materials for Li-ion batteries, but their conversion-type lithiation mechanism induces structural and morphological changes, limiting their cycling stability. Our findings now suggest that metal fluorides may undergo single-phase lithiation when crystallized in a pyrochlore structure, enabled by the presence of Li-ion storage sites within interconnected hexagonal channels. By conducting a detailed analysis of pyrochlore iron(III) hydroxy fluorides during lithiation using operando X-ray absorption spectroscopy, X-ray total scattering, and electron microscopy, we provide evidence for a possible single-phase lithiation mechanism and robust structural stability. These results challenge the traditional view of conversion-type lithiation in metal fluorides and highlight their potential for achieving high cycling stability and eventual commercialization in Li-ion batteries.
  • Thermal synthesis of conversion-type bismuth fluoride cathodes for high-energy-density Li-ion batteries
    Item type: Journal Article
    Baumgärtner, Julian; Krumeich, Frank; Wörle, Michael; et al. (2022)
    Communications Chemistry
    Towards enhancement of the energy density of Li-ion batteries, BiF3 has recently attracted considerable attention as a compelling conversion-type cathode material due to its high theoretical capacity of 302 mAh g(−1), average discharge voltage of ca. 3.0 V vs. Li+/Li, the low theoretical volume change of ca. 1.7% upon lithiation, and an intrinsically high oxidative stability. Here we report a facile and scalable synthesis of phase-pure and highly crystalline orthorhombic BiF3 via thermal decomposition of bismuth(III) trifluoroacetate at T = 300 °C under inert atmosphere. The electrochemical measurements of BiF3 in both carbonate (LiPF6-EC/DMC)- and ionic liquid-based (LiFSI-Pyr1,4TFSI) Li-ion electrolytes demonstrated that ionic liquids improve the cyclic stability of BiF3. In particular, BiF3 in 4.3 M LiFSI-Pyr1,4TFSI shows a high initial capacity of 208 mA g(−1) and capacity retention of ca. 50% over at least 80 cycles at a current density of 30 mA g(−1).
  • Navigating the Catholyte Landscape in All-Solid-State Batteries
    Item type: Review Article
    Baumgärtner, Julian; Šivavec, Jaka; Klimpel, Matthias; et al. (2026)
    ACS Energy Letters
    All-solid-state batteries are widely regarded as the next frontier in electrochemical energy storage, offering the potential to surpass the energy density and safety limits of conventional lithium-ion batteries. Among the factors governing their performance, paramount are the choice and functionality of the solid-state electrolyte (SSE) as a catholyte within the composite positive electrode. This perspective critically examines the applicability and potential of the three most intensively studied inorganic SSE families, namely oxides, sulfides, and chlorides, as catholytes. We discuss their respective advantages, limitations, and compatibility with common cathode active materials, as well as the remaining knowledge gaps. We then assess whether any of the current SSE classes can be employed as a stand-alone SSE for all-solid-state batteries, or whether composite architectures combining multiple SSEs will ultimately be required.
  • Dual-Layer Li Metal All-Solid-State Battery Based on an Argyrodite-type Li₆PS₅Cl Catholyte and a Garnet-type Li₇La₃Zr₂O₁₂Separator
    Item type: Journal Article
    Klimpel, Matthias; Černe, Chris; Šivavec, Jaka; et al. (2025)
    ACS Applied Energy Materials
    The integration of argyrodite-type Li6PS5Cl (LPSCl) solid-state electrolytes (SSEs) in solid-state batteries faces significant challenges due to their chemical reactivity with lithium metal, which precludes the direct use of lithium metal as an anode alongside LPSCl. In this study, we propose a compelling solution to this issue based on a dual solid-state electrolyte battery architecture. This design combines argyrodite-type LPSCl on the cathode side with a reductively stable garnet-type Li7La3Zr2O12(LLZO) SSE paired with a lithium metal anode. Through in situ synchrotron X-ray diffraction, cyclic voltammetry, and X-ray photoelectron spectroscopy, we confirmed the chemical compatibility of LPSCl and LLZO. Further validation of their electrochemical compatibility using symmetric and full-cell configurations revealed that Li/LLZO/LPSCl/LLZO/Li symmetrical cells maintain cycling stability over 330 cycles at a current density of 0.1 mA cm–2and an areal capacity of 0.5 mAh cm–2. The measured interfacial resistance between the LLZO and LPSCl layers was 341 Ω cm2. When paired with a LiNi0.8Mn0.1Co0.1O2(NMC811) cathode active material, the proposed dual-layer Li–metal all-solid-state battery demonstrated high initial charge-storage capacities of 184 mAh gNMC–1and Coulombic efficiency (>99.8%) over 375 cycles at a 0.2 C rate under a minimal applied stack pressure of 1 MPa and a temperature of 75 °C.
Publications 1 - 5 of 5