The cathode of bulk‐type all‐solid‐state batteries (ASSBs) is a composite consisting of cathode active material (CAM) particles and solid electrolyte (SE) particles. Since ASSBs are usually fabricated and cycled under pressure, it is important to achieve a better understanding of the influence of pressure on the electronic and ionic transport in CAM/SE composites. However, experimental values for pressure‐dependent electronic and ionic conductivities of CAM/SE composites are scarce. Therefore, we have carried out pressure‐dependent impedance spectroscopic measurements during compaction of composite powders under an increasing fabrication pressure up to 663 MPa. The composites contained four different types of LiNi0.6Mn0.2Co0.2O2 (NMC622) cathode active material particles: (i) single‐crystalline and uncoated, (ii) single‐crystalline and coated with LiNbO3, (iii) polycrystalline and uncoated, and (iv) polycrystalline and coated with LiNbO3. In addition, the volume fractions of CAM particles and SE particles were varied. The physical meaning of the resistances extracted from the impedance spectra were analyzed, and electronic and ionic tortuosities were calculated. A strong influence of the CAM particle morphology and coating on the microstructure of the composites was observed. Based on the results, the interrelation between composite microstructure and tortuosities is discussed.

Understanding and exploiting the multiple facets of Lewis acidity represents a topical challenge in molecular chemistry. Here we present the synthesis of well-defined bismuth compounds bearing the electron-withdrawing CF3 group as a key structural feature. Most importantly, a range of dicationic species [Bi(CF3)(L) n ]2+ could be isolated and characterized, the charge being balanced by different weakly coordinating anions (L = neutral ligand). The dicationic species are highly Lewis acidic (culminating in Lewis superacidity) and show the unusual ability to strongly activate two soft Lewis bases in parallel. The strong Lewis acidity was translated into a remarkable catalytic activity in the reduction of phosphane oxides.

The power density of bulk-type all-solid-state batteries (ASSBs) depends on the mechanical contacts between the solid particles inside the battery and is thus strongly influenced by the fabrication pressure of the battery and by the stack pressure during cycling. In order to achieve a better understanding of the electrochemical processes in ASSBs, we combine three-electrode impedance measurements with a variation of the stack pressure and of the thickness of the composite cathode. The analysis of the thickness-dependent impedance of the composite cathode in the framework of a transmission-line model allows for a determination of the pressure-dependent exchange current density between cathode active material particles and solid-electrolyte particles. Furthermore, we find that the impedance of the In-Li anode decreases with increasing stack pressure and with increasing degree of lithiation. This is explained in the framework of a heterogeneous interphase model for the anode/separator interface in combination with a solid solution-type chemical Li diffusion in the In-Li anode close to the interface.

Highly concentrated electrolytes (HCEs) exhibit promising properties for battery applications, such as low vapor pressure, high thermal stability and good compatibility with electrode materials. However, the charge and mass properties of HCEs in batteries are strongly influenced by volume conservation constraints as well as by interionic Coulomb interactions and cation-solvent interactions. In order to obtain a better understanding of the influence of volume conservation and different types of interactions on correlated movements of ions and solvent molecules as well as on the resulting transport properties, dynamic Monte Carlo simulations of highly concentrated electrolytes were carried out. Diffusion coefficients and Onsager transport coefficients were calculated for variable molar ratios of salt to solvent, variable partial volume ratios of solvent molecules to anions and for variable interaction strengths. The simulation results were compared to recent experimental results.

The solid electrolyte interphase (SEI) is a passivation layer in lithium-ion batteries, which has a strong impact on the battery lifetime. The SEI is formed by reductive decomposition of the electrolyte at the graphite particles of the anode during the first charging of the battery [1-2]. In the ideal case, the SEI passivates the electrode completely against further electrolyte decomposition. However, a slow yet significant long-term growth of real SEIs is observed, which contributes to battery aging [3-4]. The transport and reaction mechanism in the SEI governing the passivation properties are not well understood. Here, we elucidate transport and reaction processes during the formation of model-type SEIs by combining generator-collector experiments with a transport and reaction model [5-6]. In the generator-collector experiments, we use a four-electrode-based setup to compare the electrolyte reduction current with a redox molecule reduction current at the SEI-covered electrode. We find that the current ratio depends on the SEI formation potential as well as on the formation time. The experimental results are compared to a transport and reaction model predicting four distinct transport and reaction regimes depending on the rate constant for the molecule-electron reaction. Using this combined approach, we obtain good estimates for the transport coefficients of both electrons and molecules inside the SEI. References [1] S. An, J. Li, C. Daniel, D. Mohanty, S. Nagpure, and D. L. Wood, Carbon 2016 , 105, 52–76. [2] E. Peled, S. Menkin, J. Electrochem. Soc . 2017 , 164, A1703-A1719. [3] P. Keil, S. F. Schuster, J. Wilhelm, J. Travi, A. Hauer, R. C. Karl, A. Jossen, J. Electrochem. Soc. 2016 , 163, A1872-A1880. [4] F. Single, A. Latz, B. Horstmann, ChemSusChem 2018 , 11, 1950–1955. [5] F. T. Kraus, I. Pantenburg, V. Lehmann, M. Stich, J. O. Weiershäuser, A. Bund, B. Roling, J. Am. Chem. Soc . 2024 , 146, 19009-19018. [6] F. T. Kraus, A. Duncker, B. Roling, ChemSusChem 2025 , e202402468. Figure 1

Composite cathodes of all-solid-state batteries (ASSBs) consist of cathode active material (CAM) particles and solid electrolyte (SE) particles. Since ASSBs are typically cycled under external pressure, pressure-dependent electronic transport in the CAM phase and ionic transport in the SE phase play an important role in the battery performance. In order to better understand the relationship between conductivity, porosity, and pressure during the compression of particles, we have built a test station for simultaneous in situ measurements of conductivity and porosity under variable pressure. We illustrate the design of this test station, and we show exemplary results for the microcrystalline solid electrolyte Li5.5PS4.5Cl1.5 and for the polycrystalline cathode active material LiNi0.6Mn0.2Co0.2O2. The results indicate two distinct porosity regimes: a high-porosity regime, with the conductivity being governed by the interfacial contacts between the particles, and a low-porosity regime with the conductivity being governed by the void space between the particles.

Highly concentrated salt solutions are promising electrolytes for battery applications due to their low flammability, their high thermal stability, and their good compatibility with electrode materials. Understanding transport processes in highly concentrated electrolytes is a challenging task, since strong ion-ion and ion-solvent interactions lead to highly correlated movements on the microscopic scale. Here, we use an experimental overdetermination method to obtain accurate Onsager transport coefficients for concentrated binary electrolytes composed of either sulfolane (SL) or dimethyl carbonate (DMC) as solvent and either LiTFSI or LiFSI as salt. NMR-based electrophoretic mobilities demonstrate that volume conservation applies as a governing constraint for the transport. This fact allows to calculate the Onsager coefficients sigma+0, sigma-0 and sigma 00 related to the solvent. A parameter gamma is then defined, which is a measure for the relevance of a vehicular Li+-solvent transport mechanism. We analyze the influence of the salt anion and of the solvent on dynamic correlations and transport mechanisms. In the case of the sulfolane-based electrolytes, the gamma parameter reaches values up to 0.38, indicating that Li+-sulfolane interactions are stronger than Li+-anion interactions and that vehicular Li+-sulfolane transport plays a significant role. In the case of DMC-based electrolytes, the gamma parameter is close to zero, suggesting balanced Li+-DMC vs. Li+-anion interactions and virtually uncorrelated movements of Li+ ions and DMC molecules.

Good passivation properties of the solid electrolyte interphase (SEI) on the graphite-based negative electrode are essential for a long cycle life of lithium-ion batteries. Nevertheless, the underlying electron and molecule transport mechanisms inside the SEI are poorly understood. Here, we elucidate transport and reaction in model-type SEIs formed at different electrode potentials by combining generator-collector experiments and electrochemical impedance spectroscopy with a diffusion-reaction modeling approach. In the generator-collector experiments, we use a four-electrode-based setup to compare the electrolyte reduction current density with a redox molecule (ferrocenium Fc+) reduction current density at an SEI-covered glassy carbon electrode. We find that the current density ratio depends on the SEI formation potential as well as on the formation time. The experimental results are compared to the prediction of a transport and reaction model, which accounts for reduction reactions inside the SEI as well as in the double layer at the SEI | bulk electrolyte interface. This model predicts four distinct diffusion and reaction regimes depending on the rate constant for the molecule-electron reaction. Using this combined approach, we obtain good estimates for the transport coefficients of electrons and molecules inside the SEI.

7Li NMR diffusometry and relaxometry are combined with electrochemical impedance spectroscopy to compare the mechanisms for the dynamics and transport of lithium ions in disordered and crystalline electrolytes with argyrodite composition Li5.5PS4.5Cl1.5. The dc conductivity of a disordered sample prepared by ball milling amounts to 0.76 mScm-1 at room temperature, which is substantially lower than that of two previously studied crystalline argyrodites differing in the order of the anion sublattice due to various heat treatments. However, the activation energy of the dc conductivity is smaller for ball-milled disordered Li5.5PS4.5Cl1.5 (E_dc= 0.35 eV) than for both crystalline compounds (E_dc= 0.38 eV). 7Li NMR field-gradient measurements of the self-diffusion coefficient D and its activation energy E_D confirm these findings and, furthermore, reveal different Haven ratios. 7Li NMR field-cycling relaxometry shows that the lithium ion jumps in ball-milled Li5.5PS4.5Cl1.5 are described by very broad dynamical susceptibilities arising from a temperature-independent Gaussian-like distribution of activation energies g(E_a) with a mean value of E_m= 0.43 eV, while the susceptibilities indicated a high-energy cutoff for the crystalline electrolytes. Based on different relations between the activation energies for the conductivity, diffusivity and jumps, we discuss that the shape and exploration of the energy landscapes of ball-milled and crystalline Li5.5PS4.5Cl1.5 samples strongly differ. Moreover, significant differences in the preexponential factor of the dc conductivity, the Haven ratio and the single-particle correlation factor point to distinct types of anion lattice disorder of the ball-milled disordered and heat-treated crystalline samples.

The solid electrolyte interphase (SEI) on the anode of lithium-ion batteries (LIBs) has been studied thoroughly due to its crucial importance to the battery’s long-term performance. At the same time, most studies of the SEI apply ex situ characterization methods, which may introduce artifacts or misinterpretations as they do not investigate the SEI in its unaltered state immersed in liquid battery electrolyte. Thus, in this work, we focus on using the non-destructive combination of electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D) and impedance spectroscopy (EIS) in the same electrochemical cell. EQCM-D can not only probe the solidified products of the SEI but also allows for the monitoring of viscoelastic layers and viscosity changes of the electrolyte at the interphase during the SEI formation. EIS complements those results by providing electrochemical properties of the formed interphase. Our results highlight substantial differences in the physical and electrochemical properties between the SEI formed on copper and on amorphous carbon and show how formation parameters and the additive vinylene carbonate (VC) influence their growth. The EQCM-D results show consistently that much thicker SEIs are formed on carbon substrates in comparison to copper substrates.

For modeling electrochemical processes in all-solid-state batteries, reliable values for the electronic conductivity of cathode active materials (CAM) are of the utmost importance. Published values for a specific CAM vary by typically many orders of magnitude. Therefore, we carried out a systematic study on the influence of various experimental parameters on the effective electronic conductivity of CAM pellets. These parameters are applied stack pressure, Ni content of CAM, CAM particle morphology, particle coating, and heat treatment. Pellets of fully lithiated and uncoated Ni-rich NMC particles reach effective electronic conductivities sigma eon eff in the range of 10-1 S/cm at high pressures and 10-2 S/cm at low pressures. Particle coating by LiNbO3 lowers sigma eon eff by half an order to 1 order of magnitude. While heat treatment at 900 degrees C is capable of removing surface impurities on the CAM particle, it also leads to increased Li/Ni disorder in the bulk of the particles.

Its crucial importance to the long-term operation of lithium-ion batteries has made the solid electrolyte interphase (SEI) the subject of intensive research efforts. These investigations are challenging, however, due to the very complex and fragile nature of this layer. With its typical thickness being in the range of some 10 nm and its chemical make-up being highly sensitive to even the smallest amounts of impurities, it becomes clear that artifacts are easily introduced in investigations of the SEI, especially if the measurements are performed ex situ. To help ameliorate these issues, we herein report a combination of non-destructive operando techniques that can be employed simultaneously in the same electrochemical cell to provide a plethora of physical, morphological, and electrochemical data on the macroscopic and microscopic scale. These techniques encompass atomic force microscopy (AFM), electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D), and impedance spectroscopy (EIS). This work focuses on how to combine these techniques in a single electrochemical cell, which is suitable to study SEI formation while avoiding noise, crosstalk, inhomogeneous SEI formation, and other pitfalls.

High-voltage cathode active materials, such as LiNi0.5Mn1.5O4 (LNMO), are of major interest for the development of high-energy lithium-ion batteries. However, it has been reported that composite cathodes based on high-voltage active materials suffer from high impedances and low rate capabilities. The origin of the high impedances has not yet been clarified. Here, we use a combination of electrochemical impedance spectroscopy (EIS), focused ion beam/scanning electron microscopy/energy-dispersive X-ray spectroscopy (FIB/SEM/EDX) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) for showing that in the case of LNMO-based cathodes, a major part of the cathode impedance is related to the formation of a passivating interphase on the Al current collector. Remarkably, the impedance of this interphase can be mitigated by the targeted formation of a distinct passivating interphase, namely on the surface of the LNMO particles. The interplay between these interphases is discussed.

In lithium-ion batteries, the solid electrolyte interphase (SEI) passivates the anode against reductive decomposition of the electrolyte but allows for electron transfer reactions between anode and redox shuttle molecules, which are added to the electrolyte as an internal overcharge protection. In order to elucidate the origin of these poorly understood passivation properties of the SEI with regard to different molecules, we used a four-electrode-based generator-collector setup to distinguish between electrolyte reduction current and the redox molecule (ferrocenium ion Fc+) reduction current at an SEI-covered glassy carbon electrode. The experiments were carried out in situ during potentiostatic SEI formation close to battery operation potentials. The measured generator and collector currents were used to calculate passivation factors of the SEI with regard to electrolyte reduction and with regard to Fc+ reduction. These passivation factors show huge differences in their absolute values and in their temporal evolution. By making simple assumptions about molecule transport, electron transport, and charge transfer reaction rates in the SEI, distinct passivation mechanisms are identified, strong indication is found for a transition during SEI growth from redox molecule reduction at the electrode | SEI interface to reduction at the SEI | electrolyte interface, and good estimates for the transport coefficients of both electrons and redox molecules are derived. The approach presented here is applicable to any type of electrochemical interphase and should thus also be of interest for interphase characterization in the fields of electrocatalysis and corrosion.

The interlaboratory comparability and reproducibility of all-solid-state battery cell cycling performance are poorly understood due to the lack of standardized set-ups and assembly parameters. This study quantifies the extent of this variability by providing commercially sourced battery materials-LiNi0.6Mn0.2Co0.2O2 for the positive electrode, Li6PS5Cl as the solid electrolyte and indium for the negative electrode-to 21 research groups. Each group was asked to use their own cell assembly protocol but follow a specific electrochemical protocol. The results show large variability in assembly and electrochemical performance, including differences in processing pressures, pressing durations and In-to-Li ratios. Despite this, an initial open circuit voltage of 2.5 and 2.7 V vs Li+/Li is a good predictor of successful cycling for cells using these electroactive materials. We suggest a set of parameters for reporting all-solid-state battery cycling results and advocate for reporting data in triplicate.

We combine Li-7 NMR relaxometry and diffusometry with electrochemical impedance spectroscopy to unravel the mechanisms for the dynamics and transport of lithium ions in the lithium-deficient and halide-rich argyrodite Li5.5PS4.5Cl1.5. In particular, we determine the effects of heat treatment on the cooperativity, heterogeneity, and subdiffusion of lithium ion motion. We find that heat treatment results in an enhancement of the dc conductivity by a factor of six to a high room-temperature value of sdc = 14.9 mScm(-1), whereas the change of the Li-7 NMR self-diffusion coefficients D is considerably smaller. Accordingly, heat-treated Li5.5PS4.5Cl1.5 shows a very small Haven ration of H-R = 0.13 indicative of a high cooperativity of lithium ion dynamics. Moreover, after heat treatment, the collective correlation factor f(I) becomes very small, which is related to a strongly reduced relevance of subdiffusive lithium ion dynamics. However, heat treatment does not affect the activation energies, which are in the range E-a = 0.34 0.40 eV for the dc conductivity sdc, the diffusion coefficient D and also for the jump correlation time tau. Li-7 NMR field-cycling relaxometry allows for a characterization of the lithium ion jumps based on a frequency-dependent dynamical susceptibility. We find that the susceptibility peak has a strongly asymmetric shape with a hardly broadened low-frequency flank and a strongly broadened high-frequency flank, reflecting a characteristic heterogeneity of the lithium ion dynamics, which derives from the specific cage-like arrangement of the lithium sites and the resulting difference in the rates of intra-cage and inter-cage jumps. Considering further the anion disorder in the crystal lattice, we propose that heat treatment facilitates cooperative inter-cage jumps, suppressing localized subdiffusive motion and enabling long-range ion transport along percolating pathways.