Niklas Markus Abke

The use of localized high‐concentration electrolytes (LHCEs) has emerged as a promising strategy to improve the stability of Li metal electrodes while overcoming the high viscosity and cost associated with high‐concentration electrolytes (HCEs). In this work, we investigate how electrolyte solvation structure and further physicochemical properties, like Li electrodeposition and SEI formation, evolve across a wide concentration range—from diluted electrolytes to HCEs and LHCEs—and how these changes influence Li reactivity and solid electrolyte interphase (SEI) formation in NCM ‖ Li cells. Ether‐based electrolytes composed of LiTFSI as conducting salt and 1,2‐dimethoxyethane (DME) as solvent are systematically modified using 1,1,2,2‐tetrafluoroethyl 2,2,3,3‐tetrafluoropropylether (TTE) as a non‐ion‐coordinating diluent to form LHCEs. Surface‐sensitive characterization, including time‐of‐flight secondary ion mass spectrometry, is employed to analyze the SEI composition. By correlating electrolyte concentration, solvation structure, and interfacial chemistry, this study focuses on the investigation of the Li metal surface after spontaneous formation of the SEI with the electrolytes and after electrodeposition/‐dissolution in Cu ‖ Li as well as high‐energy NCM ‖ Li cells.

Si‐based anodes (e.g., SiO _x ) can increase the specific energy of Li‐ion batteries but decrease cycle life due to volume change‐reasoned material stress, which requires continuous reformation of the solid electrolyte interphase (SEI) at the cost of active Li loss (ALL). Even in small ratios within a binary anode with graphite, Si can be exposed to a high state‐of‐charge as it can be stressed by transfer lithiation from lithiated graphite. SEI engineering via rational design of electrolyte additives can be an eligible measure, but is particularly challenging, as the SEI must effectively passivate and prevent detrimental SiO _x |LiPF ₆ contact in order to suppress failure cascades caused by generated HF (e.g., electrode crosstalk), while efficiently minimizing ALL. Also, theoretically, the recovery of the “SEI waste” stemming from the continuous SEI reformation can be advantageous and, for example, be realized via a designed and controlled electrolyte solubility, where the respective diffusion toward the cathode would compensate ALL by oxidation reactions. Here, an easily modifiable B‐based compound (dioxazaborole) is synthesized and exemplarily investigated. While it forms a partly effective SEI and can be suitable for “SEI‐waste” recovery, the remaining challenges of gassing and resistance require further design optimization, consequently highlighting the difficulty of an “allrounder” additive.

To fully utilize the electrochemical performance of Ni-rich layered oxides, it is critical to understand the particle-level degradation under harsh cycling conditions. Here, we combine single-particle inductively coupled plasma optical emission spectroscopy (SP-ICP-OES) with complementary post-mortem characterization techniques to analyze the state-of-charge (SOC) distribution and microstructural evolution of LiNi0.8Mn0.1Co0.1O2 (NMC811) particles aged across different upper cut-off voltages (UCVs) and C-rates. While harsh cycling conditions accelerate capacity fading and voltage polarization, single-particle analysis revealed a uniform, monomodal SOC distribution across the aged particles, which was confirmed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) elemental mapping, showing a uniform lateral Li distribution within the composite electrodes. Additional scanning electron microscopy (SEM) analysis after cyclic aging at high UCVs of up to 4.7 V revealed negligible particle cracking, which can be attributed to elemental modifications of the active material, as confirmed by bulk ICP-OES analysis. These findings highlight the importance of the chemomechanical interplay within Ni-rich CAM particles cycled under harsh conditions, offering insights into the role of material modifications for better state-of-the-art cathode materials in LIBs.

Nowadays, lithium ion batteries (LIBs) are dominating the rechargeable energy storage market. However, lithium/sulfur batteries (LSBs) offer higher energy densities with sulfur’s economic and ecologic advantages, but exhibit poor cyclability, capacity utilization and lifetime. The utilization of metal sulfide active materials and solid-state electrolytes (SSE) show promise to alleviate these issues but coming with their own challenges such as material integrity. This study is focused on analyzing these aging effects by utilizing high lateral and mass resolution time-of-flight-secondary ion-mass spectrometry (ToF-SIMS) imaging of focused ion beam (FIB) cross sections. By measuring the pristine components, the identification of newly formed species as well as the individual particles in a composite was enabled. This work shows among others the formation of a carbon-electrolyte interphase, the accumulation of sodium, the degradation of the metal polysulfide and the decomposition of the SSE. By revealing different aging mechanisms, this research takes part in paving the way for long-lasting, energy dense, and safe SSE LSBs as a more environmentally friendly alternative to conventional commercial LIBs.

Amorphous titanium tetrasulfide (TiS ₄ ) is investigated as a high‐capacity cathode material for sulfide‐based solid‐state batteries using Li ₆ PS ₅ Cl argyrodite as solid electrolyte. A systematic comparison between low‐energy ball milling (LBM) and high‐energy ball milling (HBM) reveals that tribochemical processing intensity determines composite microstructure and electrochemical performance. HBM‐processed composites exhibit superior homogenization confirmed by quantitative FIB‐SEM analysis, achieving discharge capacities of 1110 mAh g _S ⁻¹ at 0.05 C and 669 mAh g _S ⁻¹ at 0.5 C. Despite lower bulk electronic conductivity, HBM composites demonstrate enhanced performance consistent with shortened solid‐state diffusion lengths and increased triple‐phase boundary density. SOC‐dependent electrochemical impedance spectroscopy reveals that HBM composites accumulate only 19% impedance growth at 100% SOC over 34 cycles compared to 41% for LBM counterparts, indicating superior interfacial stability. Time‐of‐flight secondary ion mass spectrometry provides spatial evidence for heterogeneous lithiation, with codetected TiS ⁺ and Li ₃ S ⁺ species consistent with gradual structural reorganization along the conversion trajectory. Scalability is demonstrated through dry‐film electrode fabrication, and HBM‐processed cathodes achieve initial capacities of 1240 mAh g _S ⁻¹ and retain 950 mAh g _S ⁻¹ after 80 cycles. Absolute capacity values reflect the combined electrochemistry of TiS ₄ and partially decomposed Li ₆ PS ₅ Cl. This work establishes tribochemical processing as a viable strategy for optimizing conversion‐type cathodes in solid‐state batteries.

The specific energy of Li ion batteries with layered‐oxide‐based cathodes can be enhanced by enhancing charge cut‐off voltage, which increases both, mean discharge voltage and capacity. However, the increased delithiation capacity facilitates thermodynamically‐driven phase changes and increases transition metal (TM) dissolution, finally initiate a failure cascade, known as “electrode crosstalk”. This can trigger formation of high surface area lithium (HSAL), active Li/capacity loss, and consequently decrease the cycle life. Here, after screening of bio‐based additives, the maleimide (MI) is shown to be even superior compared to the effective and literature‐known TM‐scavenging additive lithium difluorophosphate (LiDFP). Although, the electrode crosstalk and the TM amount on the anode are not suppressed with MI, the anode surface remains intact, and is even free from HSAL deposits. The solid electrolyte interphase (SEI) is shown to consist from oligo and polymer‐based MI decomposition products and is concluded to scavenge TMs on the outer SEI layer via its characteristic coordinating chemistry. This way the TM diffusion toward the inner SEI layer is suppressed, where it otherwise would block the Li ⁺ pathway and initiate the well‐known failure cascades, that is, locally increase resistance, trigger HSAL formation and capacity fade, in worst case rollover failure.