Perspective on recent improvements in experiment and theory towards realizing lithium metal electrodes with liquid electrolytes.

This article discusses the options and challenges of dynamic models for the diagnosis and operation of Li-ion batteries. It provides a concise yet understandable overview on models and dynamics, and it discusses future developments needed to progress the field. The diagnosis and operation of batteries require an understanding of the main processes and their dynamics, parameters, and time constants. Processes with large time constants, such as thermal transport are equally important for safe high-performance operation as are processes with shorter time constants such as diffusion. Depending on the specific problem or operating condition, taking all of the scales into account is often unavoidable. Three separate, yet closely connected model classes are reviewed in terms of physical insight and their capabilities and limits: mechanistic models, equivalent circuit models, and data-driven models. We provide guidance for the selection of a suitable model for the particular diagnosis and operation problem of interest. The optimization of battery diagnosis and operation require versatile and simple models that span multiple time scales and allow physical insight and ease of parameterization. Fusing the existing modeling approaches may help to fully exploit their potential while integrating first-principles physical insight and measurement data.

The power-to-ammonia concept allows for the production of ammonia, one of the most produced inorganic chemicals, from air, water and (renewable) electricity. However, power-to-ammonia requires flexible operation for use with a directly intermittent renewable energy supply. In this paper, we systematically analyse the operating envelope for steady-state operation of the three bed autothermic Haber–Bosch reactor system for power-to-ammonia by pseudo-homogeneous model. Operational flexibilities of process variables, hydrogen intake and ammonia production flexibilities are analysed, along with maximum and minimum possible changes in recycle load and recycle to feed ratio for the following process variables: reactor pressure, inert gas percentage in synthesis loop, NH₃ concentration, H₂-to-N₂ ratio, total flow rate and feed temperature. Among the six process variables, inert gas fraction and H₂-to-N₂ ratio provided very high flexibilities, ca. 255% operational flexibility for Ar, up to 51 to 67% flexibility in hydrogen intake, and up to 73% reduction and 24% enhancement in ammonia production. However, a decrease in ammonia production by H₂-to-N₂ ratio significantly increases recycle load. Besides inert gas fraction and H₂-to-N₂ ratio, the total mass feed flow rate is also significant for minimum hydrogen intake and ammonia production.

This work reveals the impact of particle size distribution of spherical graphite active material on negative electrodes in lithium‐ion batteries. Basically all important performance parameters, i. e. charge/discharge characteristics, capacity, coulombic and energy efficiencies, cycling stability and C‐rate capability are shown to be affected by distribution shapes. A narrow distribution with smaller particles results in better cell performance than broader and coarser distributions. However, particle size reduction has a limitation as extremely small particles show negative effect in performance. More critically, independent of the particle size distribution, the existence of coarse particles are found to promote lithium plating, which lowers cell performance and threatens the safety of battery operation. Furthermore, impedance analysis and cycling stability show huge differences for different electrodes. Our study shows that a better understanding of the influence of particle size distribution is an important base to engineer electrodes with higher C‐rate capability, higher performance, and lower safety risk due to lithium plating.

The increasing scarcity of iridium (Ir) and its rutile-type oxide (IrO₂), the current state-of-the-art oxygen evolution reaction (OER) catalysts, is driving the transition toward the use of mixed Ir oxides with a highly active yet inexpensive metal (Ir_xM_1–xO₂). Ruthenium (Ru) has been commonly employed due to its high OER activity although its electrochemical stability in Ir-Ru mixed oxide nanoparticles (Ir_xRu_1–xO₂ NPs), especially at high relative contents, is rarely evaluated for long-term application as water electrolyzers. In this work, we bridge the knowledge gap by performing a thorough study on the composition- and phase-dependent stability of well-defined Ir_xRu_1–xO₂ NPs prepared by flame spray pyrolysis under dynamic operating conditions. As-prepared NPs (Ir_xRu_1–xO_y) present an amorphous coral-like structure with a hydrous Ir-Ru oxide phase, which upon post-synthetic thermal treatment fully converts to a rutile-type structure followed by a selective Ir enrichment at the NP topmost surface. It was demonstrated that Ir incorporation into a RuO₂ matrix drastically reduced Ru dissolution by ca. 10-fold at the expense of worsening Ir inherent stability, regardless of the oxide phase present. Hydrous Ir_xRu_1–xO_y NPs, however, were shown to be 1000-fold less stable than rutile-type Ir_xRu_1–xO₂, where the severe Ru leaching yielded a fast convergence toward the activity of monometallic hydrous IrO_y. For rutile-type Ir_xRu_1–xO₂, the sequential start-up/shut-down OER protocol employed revealed a steady-state dissolution for both Ir and Ru, as well as the key role of surface Ru species in OER activity: minimal Ru surface losses (<1 at. %) yielded OER activities for tested Ir_0.2Ru_0.8O₂ equivalent to those of untested Ir_0.8Ru_0.2O₂. Ir enrichment at the NP topmost surface, which mitigates selective subsurface Ru dissolution, is identified as the origin of the NP stabilization. These results suggest Ru-rich Ir_xRu_1–xO₂ NPs to be viable electrocatalysts for long-term water electrolysis, with significant repercussions in cost reduction.