Myth and Reality of a Universal Lithium-Ion Battery Electrode Design Optimum: A Perspective and Case Study

The quest toward optimal electrode design for energy‐ and power‐demanding applications involves besides experimental effort also less resource‐intensive model‐based studies. The diversity of optimization objectives and benchmark systems complicates the practical utilization of available methods and gained knowledge. Despite the increasing importance of fast charging, electrode design studies commonly focus only on discharge characteristics. This paper features, besides an overview and perspective of electrode structuring concepts and optimization pathways, a model‐based full cell parameter screening of two‐layered electrodes for charge and discharge. The small fraction of cells with superior performance among the evaluated configurations underlines the importance of a joint experimental and model‐based electrode design optimization. The results further indicate that the performance of cell designs tailored for fast charge or fast discharge differs substantially; the gap widens if charging is terminated below 0 V versus Li/Li+ to prevent lithium plating. The broad parameter screening is complemented by a high‐resolution half cell parameter study. Their comparison underlines that the benefit of electrode structuring depends heavily on the study extent and the chosen benchmark. Furthermore, the importance of the parameter space surrounding an optimal electrode design for production with process tolerances is highlighted

Species Distribution During Solid Electrolyte Interphase Formation on Lithium Using MD/DFT-Parameterized Kinetic Monte Carlo Simulations

Lithium metal batteries are one of the promising technologies for future energy storage. One open challenge is the generation of a stable and well performing Solid Electrolyte Interphase (SEI) between lithium metal and electrolyte. Understanding the complex interaction of reactions at the lithium surface and the resulting SEI is crucial for knowledge-driven improvement of the SEI. This study reveals the internal species distribution and geometrical aspects of the native SEI during formation by model-based analysis. To achieve this, a combination of molecular dynamics, density functional theory, and stand-alone 3D-kinetic Monte Carlo simulations is used. The kinetic Monte Carlo model determines the SEI growth features over a long time and length scale so that the SEI can be analyzed quantitatively. The simulation confirms the frequently postulated layered SEI structure arising from the decomposition of an ethylene carbonate/lithium hexafluorophosphate (2 M) electrolyte with lithium metal. These layers are not clearly separated, which is contrary to what is often reported. The gradient distribution of the species within the SEI therefore corresponds to a partly mosaic structured SEI at the borders of the layers. At the lithium surface, an inorganic layer of lithium fluoride and then lithium carbonate is observed, followed by an organic, more porous SEI layer consisting of lithium ethylene dicarbonate. Simulations further reveal the strong prevalence of corrosion processes of the metal, which provide more than 99% of the lithium for the SEI reaction processes. The salt contributes less than 1% to the SEI formation. Additionally, SEI formation below and above the initial interface was observable. The here presented novel modeling approach allows an unprecedented in-depth analysis of processes during native SEI formation that can be used to improve design for high battery performance and durability

Side by Side Battery Technologies with Lithium‐Ion Based Batteries

In recent years, the electrochemical power sources community has launched massive research programs, conferences, and workshops on the “post Li battery era.” However, in this report it is shown that the quest for post Li‐ion and Li battery technologies is incorrect in its essence. This is the outcome of a three day discussion on the future technologies that could provide an answer to a question that many ask these days: Which are the technologies that can be regarded as alternative to Li‐ion batteries? The answer to this question is a rather surprising one: Li‐ion battery technology will be here for many years to come, and therefore the use of “post Li‐ion” battery technologies would be misleading. However, there are applications with needs for which Li‐ion batteries will not be able to provide complete technological solutions, as well as lower cost and sustainability. In these specific cases, other battery technologies will play a key role. Here, the term “side‐by‐side technologies” is coined alongside a discussion of its meaning. The progress report does not cover the topic of Li‐metal battery technologies, but covers the technologies of sodium‐ion, multivalent, metal–air, and flow batteries

The passivity of lithium electrodes in liquid electrolytes for secondary batteries

Rechargeable Li metal batteries are currently limited by safety concerns, continuous electrolyte decomposition and rapid consumption of Li. These issues are mainly related to reactions occurring at the Li metal–liquid electrolyte interface. The formation of a passivation film (that is, a solid electrolyte interphase) determines ionic diffusion and the structural and morphological evolution of the Li metal electrode upon cycling. In this Review, we discuss spontaneous and operation-induced reactions at the Li metal–electrolyte interface from a corrosion science perspective. We highlight that the instantaneous formation of a thin protective film of corrosion products at the Li surface, which acts as a barrier to further chemical reactions with the electrolyte, precedes film reformation, which occurs during subsequent electrochemical stripping and plating of Li during battery operation. Finally, we discuss solutions to overcoming remaining challenges of Li metal batteries related to Li surface science, electrolyte chemistry, cell engineering and the intrinsic instability of the Li metal–electrolyte interface