Bernhard Roling

Compounds featuring the [Bi(CF ₃ )(L) _n ] ²⁺ ions have been investigated (L = neutral ligand). The dications are exceptionally strong Lewis acids, engage in parallel substrate activation, and are highly active catalysts in phosphane oxide reduction.

Deprotonation experiments of SEIs show that fixed surface charges in narrow pores can reduce ionic conductivity, contradicting existing models of ion transport through charged pores. Here, an alternative model based on Coulomb trapping is presented.

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 Li_5.5PS_4.5Cl_1.5 and for the polycrystalline cathode active material LiNi_0.6Mn_0.2Co_0.2O₂. 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.

We used dynamic Monte Carlo simulations to study the influence of volume conservation, Coulomb interactions and attractive cation–solvent interactions on the transport properties of highly concentrated electrolytes.

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.

Composite cathodes of all-solid-state batteries (ASSBs) consists of cathode active material (CAM) particles and solid electrolyte (SE) particles. Since ASSBs are typically cycled under an external pressure, the pressure-dependent electronic transport inside the CAM phase and ionic transport inside the SE phase play an important role for 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.

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.

The solid electrolyte interphase (SEI) on the anode of lithium-ion-batteries (LIB) 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 additives influence their growth. The EQCM-D results show consistently that much thicker SEIs are formed on carbon substrates in comparison to copper substrates.

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.