Christian Baur

Deep eutectic solvents (DESs) are an emerging class of ionic liquids with high tunability and promise for battery applications. In this study, we investigated acetamide‐based DESs for Zn batteries, focusing on a synergistic mixture of two known acetamide (Ace)‐based DESs: and . By combining these two DESs in various ratios, we aimed to enhance ionic conductivity and optimize electrochemical performance while addressing corrosion concerns. The resulting ternary mixtures exhibit superior ionic mobility, with the highest conductivity observed for , which balances performance and stability. However, increased ionic mobility introduces crystallization challenges, limiting liquid‐phase stability. Despite these challenges, the optimized DES mixture demonstrates excellent cycling performance with reduced overpotentials and acceptable corrosion levels, offering a viable pathway for scalable Zn battery applications.

Scanning 3DXRD was used to visualize strain localization at grain boundaries with a high spatial resolution of 100 nm.

Anionic redox activity in Li-rich cathode materials is a topic of intense interest because it presents the potential to increase the energy density of Li-ion batteries. An in-depth understanding of the anionic redox activity such as lithiation/voltage levels in which peroxide and superoxide formations take place and the reversibility of the reactions are important. In this work, we present a combined computational and experimental analysis that probes the formation of anionic redox species during electrochemical cycling. We report the formation of peroxides and superoxides in Li₂VO₂F when charged up to a relatively low potential of 4.1 V for Li-rich cathode materials. The formation of superoxide is not entirely reversible upon discharge, which is closely linked to the vanadium dissolution and limited reversibility of the vanadium redox couple. This article provides new insights and fundamental understanding of anionic redox activities in disordered Li-rich materials.

Li‐rich disordered rock salt (DRS) materials are new promising high‐capacity cathode candidates for Li‐ion batteries. DRS structures were initially assumed to have a completely random cation and anion distribution, but recent reports suggest that some of these structures can exhibit local atomic arrangements, or short‐range ordering (SRO). Here, we prove the existence of SRO in the Li‐rich DRS material Li₂VO₂F by employing Raman spectroscopy supported by density functional theory (DFT) calculations. Our results suggest that this combination of Raman spectroscopy with computational tools is useful for SRO estimation in this new class of Li‐rich DRS cathode materials.

Promising theoretical capacities and high voltages are offered by Li-rich disordered rocksalt oxyfluoride materials as cathodes in lithium ion batteries. However, as has been discovered for many other Li-rich materials, the oxyfluorides suffer from extensive surface degradation, leading to severe capacity fading. In the case of Li₂VO₂F, we have previously determined this to be a result of detrimental reactions between an unstable surface layer and the organic electrolyte. Herein, we present the protection of Li₂VO₂F particles with AlF₃ surface modification, resulting in a much enhanced capacity retention over 50 cycles. While the specific capacity for the untreated material drops below 100 mA h g^-1 after only 50 cycles, the treated materials retain almost 200 mA h g^-1. Photoelectron spectroscopy depth profiling confirms the stabilisation of the active material surface by the surface modification and reveals its suppression of electrolyte decomposition.

Disordered rock salt Li₂VO₂F cathode material for lithium-ion batteries was investigated using operando X-ray diffraction and total scattering in order to gain insight in the structural changes of the short-range and long-range order during electrochemical cycling. The X-ray powder diffraction data shows the well-known pattern of the disordered rock salt cubic structure, whereas pair distribution function (PDF) analysis reveals significant deviations from the ideal cubic structure. During battery operation, a reversible rock salt to amorphous phase transformation is observed, upon Li extraction and reinsertion. The X-ray total scattering data show strong indications of the formation of tetrahedrally coordinated V in the charged electrode material. The results show that disordered rock salt Li₂VO₂F material undergoes a hidden structural rearrangement during battery operation.

Facile and reversible insertion and extraction of Li+ was recently demonstrated to be possible with a new cation-disordered rock salt (DRS) LiVO₂ compound (Space Group (SG): Fm3 ̅m). Further structural analyses describing the links between the well-known layered trigonal structure of LiVO₂ (space group:R3 ̅m) and DRS LiVO₂ synthesized by mechanical ball milling are presented. Optimized Rietveld refinements of the X-ray diffraction patterns confirm the formation of LiVO₂ in disordered rock salt phase. We observed the phase transition from the trigonal to cubic structure and the evolution of cell parameters during the ball-milling process using ex situ X-ray diffraction. The reverse phase transition from cubic to trigonal structure is achieved via thermal treatment, which was confirmed via differential scanning calorimetry and in situ X-ray diffraction experiments. The phase transition to trigonal structure suggests the metastability of the cubic structure. An exhaustive computational analysis based on a cluster expansion model trained by density functional theory calculations is conducted to confirm the metastability. The presented methods and results show that different (meta-)stable phases can be achieved depending on the synthesis method, which is an important aspect to consider in investigating the properties of the new DRS cathode materials for Li-ion batteries.

Biowaste eggshell can be used as a cathode while in its calcined form and it is found to be suitable as an anode in an electrochemical cell. This not only enables energy to be stored reversibly but also achieves waste management and sustainability goals by redirecting material away from landfill. Biowaste eggshell comprises 94% calcium carbonate (CaCO₃; calcite), an attractive divalent ion source as a viable option for energy storage. X-ray diffraction and electron microscopy coupled with energy dispersive analyses of the calcined (thermally decomposed) biowaste eggshell show that CaO has been formed and the reaction is topotactic. Field emission scanning electron microscopy (FESEM) images of the textural relationship show that the thermal decomposition of calcite resulted in a change in morphology. High-resolution XPS spectra of the C 1s core level from the CaCO₃ and CaO shows that there is a chemical difference in the carbon environments and the total atomic fraction of Ca for each sample with that of carbonate and oxygen varies. In a three-electrode configuration, a working electrode of CaCO₃ is found to be electrochemically active in the positive region, whereas a CaO electrode is active in the negative region. This indicates the potential use of eggshell-derived materials for both cathode and anode. Both the electrodes exhibited a quasi-box-shaped potentiostatic curve implying a capacitor-type behaviour. The CaCO₃ cathode possesses a modest discharge capacitance of 10 F g⁻¹ but the CaO anode showed excellent capacitance value of 47.5 F g⁻¹. The CaO electrode in both positive and negative regions, at a current density of 0.15 A g⁻¹ exhibited 55 F g⁻¹ with a retention of nearly 100% after 1000 cycles. At a very low sweep rate of 0.5 mV s⁻¹, the CaO electrode showed typical redox-type behaviour with well-defined peaks illustrating battery-type behaviour. The outcome of the calcite/CaO transformation, exhibiting technological importance for energy storage applications, may help to re-evaluate biowaste before throwing it away. The current work explores the viability of eggshell derived materials as a cathode/anode for use in batteries and capacitors.

Lithium-rich transition metal disordered rock salt (DRS) oxyfluorides have the potential to lessen one large bottleneck for lithium ion batteries by improving the cathode capacity. However, irreversible reactions at the electrode/electrolyte interface have so far led to fast capacity fading during electrochemical cycling. Here, we report the synthesis of two new Li-rich transition metal oxyfluorides Li₂V_0.5Ti_0.5O₂F and Li₂V_0.5Fe_0.5O₂F using the mechanochemical ball milling procedure. Both materials show substantially improved cycling stability compared to Li₂VO₂F. Rietveld refinements of synchrotron X-ray diffraction patterns reveal the DRS structure of the materials. Based on density functional theory (DFT) calculations, we demonstrate that substitution of V³⁺ with Ti³⁺ and Fe³⁺ favors disordering of the mixed metastable DRS oxyfluoride phase. Hard X-ray photoelectron spectroscopy shows that the substitution stabilizes the active material electrode particle surface and increases the reversibility of the V³⁺/V⁵⁺ redox couple. This work presents a strategy for stabilization of the DRS structure leading to improved electrochemical cyclability of the materials.