Helmholtz-Institute Münster

Research and development of non-aqueous electrolyte solutions are essential for practical advancement towards the production of high-energy lithium metal batteries (LMBs). An ideal LMB electrolyte solution should enable highly efficient, uniform and prolonged lithium metal plating and stripping, preserve the electrodes' electro(chemo)mechanical properties and ensure compatibility with all cell components. However, despite extensive research efforts, scientists have yet to achieve an electrolyte design that meets these requirements simultaneously. Here, by examining the nanoengineering aspects of various non-aqueous electrolyte solution designs, we elucidate the understanding of the nanoscale physicochemical and electrochemical processes taking place in LMBs, which are mainly governed by the thermodynamic and kinetic properties of the electrolyte system. We also explore emerging research directions and propose an accelerated, iterative framework that integrates nanoengineering principles with machine learning, high-throughput computation and experimentation to facilitate the development of next-generation non-aqueous electrolyte solutions for practical LMBs.

Li-Ion Batteries Si-based anodes can increase the energy density of Li ion batteries but require re-formation of solid electrolyte interphase (SEI) via reduction reactions, which consumes active Li, thus capacity. Interestingly, some apparently "dead" SEI species can cross over to the cathode and recover the apparently lost active Li via oxidation reactions. In article number e202500637, Johannes Kasnatscheew and co-workers.

Mixed-anion strategies have proven effective in designing materials with diverse functionalities, particularly for enhancing the ionic conductivity in sodium halides. While prior efforts have largely focused on incorporating oxide anions into halide frameworks, the exploration of other anions, such as sulfides, has recently begun. According to Pauling’s third rule, highly charged cations disfavor ordered edge- or face-sharing polyhedra, making mixed-anion substitution an effective route to promote the structural disorder needed for fast Na+ transport. Here, we contribute to these emerging efforts by investigating sulfide incorporation in amorphous Ta5+ containing Na–halide frameworks. Furthermore, we reveal the formation of an amorphous matrix with structural motifs distinct from those of oxychlorides. These unique features facilitate Na+ transport, achieving room-temperature ionic conductivity of 3.8 mS·cm–1.

Argyrodite-type Ag-based sulfides combine exceptionally low lattice thermal and high ionic conductivity, making them promising candidates for thermoelectric and solid-state energy applications.

The entropy variation Δ S poses a fundamental characteristic of lithium-ion batteries due to its influence on their thermal behavior. This study presents an extensive open source dataset containing potentiometric entropy variation measurements on two commercially available cell types. The experimental campaign includes 20 temperature steps over 9 different states of charge (SoC) approached in charging and discharging direction. Further measurements on half cell level were conducted in order to investigate the electrodes’ contribution to the full cell entropy. In addition, a reduced testing regime was applied to 6 degraded cells aged via various aging regimes. The measurements were analyzed to quantify the influence of SoC, non-linearity, hysteresis, temperature-path-dependency and aging on the entropy variation. Comparing the results to literature, the expected influence of both SoC and load-history-dependent hysteresis were confirmed. Regarding the influence of non-linearity, no significant effect was determined for the given dataset. The effects temperature-path-dependency observed in literature were successfully reproduced. However, the proposed loop-like relationship resembling common hysteresis phenomena could not be verified. The reconstruction of the full cell entropy variation curve from half cell measurements was successfully conducted for cells in pristine condition, while its application on aged specimens proved difficult likely due to challenges during determination of the electrode balancing. • Open-source dataset with entropy variation measurements for two cell types. • Electrode entropy measurements and reconstruction of full cell entropy variation. • Analysis of aging, temperature and hysteresis effects on the entropy variation.

The mechanical stress resulting from volume changes during lithiation and delithiation cycles of silicon-containing anodes in high-energy-density lithium ion batteries (LIBs) causes continuous solid electrolyte interphase (SEI) breakdown. This results in constant SEI reformation and thus, loss of active lithium, ultimately reducing battery lifetime. To address these challenges, tailored electrolyte formulations incorporating molecular additives are being increasingly investigated to improve SEI stability and enhance electrochemical performance.In recent years, molecular electrolyte additives such as dioxazolones,[1,2] O-Carboxyanhydrides (OCAs),[3] and N-Carboxyanhydrides (NCAs)[4,5] have been introduced to enhance SEI robustness in LIBs. Herein, a novel and easily synthesizable class of compounds, dioxazaboroles – specifically, 2,5-diphenyl-1,3,4,2-dioxazaborole (DOB) – as an electrolyte additive for NCM 523 || 10%SiO x -graphite lithium ion cells is presented. The effects of DOB on SEI formation, long-term cycling performance, self-discharge, gassing behavior, and interphase chemistry are investigated.This work demonstrates that DOB effectively enhances SEI durability, leading to a prolonged cycle life compared to cells with fluoroethylene carbonate (FEC) as a state-of-the-art additive. The improved performance is attributed to the DOB-derived SEI, which provides enhanced stabilization against the large volumetric fluctuations of the silicon-containing anode – thus contributing to the longevity of the cell. However, the instability of this SEI at elevated temperatures and high states of charge leads to increased self-discharge and more gassing compared to FEC-containing cells.This study highlights the critical role of rational electrolyte additive design and the necessity for comprehensive additive evaluations that go beyond cycle life improvements to ensure overall performance enhancements while maintaining practicability in terms of price and synthesis effort.

Lithium-based batteries are currently the leading battery technology. To develop more diverse and sustainable energy storage solutions, alternative battery chemistries and materials must be explored. In this work, we investigated the aliovalent substitution series of NASICON-type Ca(1+x)/2InxZr2–x(PO4)3 (x = 0, 0.125, 0.25, 0.375, 0.5, 0.75, and 1). To establish the structure–transport relations in the materials, a combination of impedance spectroscopy, direct current (DC) polarization measurements, and temperature-dependent powder X-ray diffraction (XRD) measurements up to 800 °C was used. At 800 °C, where the materials are most conductive, there is an increase of the ionic conductivity from x = 0 to 0.375, reaching a maximum of 2.4·10–4 S·cm–1. For compositions with x ≥ 0.5, however, the conductivity decreases significantly. The maximum conductivity and its subsequent decrease are linked to an interplay of crystal–chemical factors, namely, the bottleneck size and the number of available vacancies. This study shows that it is possible to increase the Ca2+ ion conductivity through aliovalent substitution; however, due to distinct, crystallographic differences, design principles from lithium- or sodium-based NASICONs may not be directly applicable to their calcium analogues.

Lithium–sulfide positive electrodes represent a promising alternative to established transition metal‐based positive electrodes due to enhanced specific capacity and sustainability. While positive electrodes containing elemental sulfur require a lithiated negative electrode, lithium–sulfide can serve as the lithium reservoir and thus be paired with bare copper electrodes in “anode‐free” or “zero‐excess” cell concepts. This boosts energy density and avoids handling of thin lithium metal electrodes. While promising electrochemical performance of “anode‐free” lithium–sulfide batteries has already been demonstrated, many reported cell configurations rely on nickel‐ instead of copper‐based negative electrodes, undermining the enhanced sustainability bestowed by lithium–sulfide positive electrodes. Demonstrating a continuous reaction between copper electrodes and soluble polysulfide species, two approaches are evaluated that restrict the migration of polysulfide species. While both, in situ polymerization of an electrolyte additive as well as electrospinning of a polymer layer at negative electrodes, enable reversible operation of copper‐based “anode‐free” lithium–sulfide batteries, the former approach offers notably enhanced capacity retention. Counterintuitively, the quantification of polysulfide distribution throughout the individual battery components reveals less confinement within the positive electrode as beneficial for the overall reversibility. This demonstrates that a balance between positive and negative electrode reversibility is required to advance “anode‐free” lithium–sulfide batteries.