Influence of inversion on Mg mobility and electrochemistry in spinels

Magnesium oxide and sulfide spinels have recently attracted interest as cathode and electrolyte materials for energy-dense Mg batteries, but their observed electrochemical performance depends strongly on synthesis conditions. Using first principles calculations and percolation theory, we explore the extent to which spinel inversion influences Mg$^{2+}$ ionic mobility in MgMn$_2$O$_4$ as a prototypical cathode, and MgIn$_2$S$_4$ as a potential solid electrolyte. We find that spinel inversion and the resulting changes of the local cation ordering give rise to both increased and decreased Mg$^{2+}$ migration barriers, along specific migration pathways, in the oxide as well as the sulfide. To quantify the impact of spinel inversion on macroscopic Mg$^{2+}$ transport, we determine the percolation thresholds in both MgMn$_2$O$_4$ and MgIn$_2$S$_4$. Furthermore, we analyze the impact of inversion on the electrochemical properties of the MgMn$_2$O$_4$ cathode via changes in the phase behavior, average Mg insertion voltages and extractable capacities, at varying degrees of inversion. Our results confirm that inversion is a major performance limiting factor of Mg spinels and that synthesis techniques or compositions that stabilize the well-ordered spinel structure are crucial for the success of Mg spinels in multivalent batteries

Der platonische Nietzsche

Mit der Behauptung, dass seine eigene Philosophie als »umgedrehter Platonismus« verstanden werden soll, stellt Nietzsche seine Beziehung zum platonischen System dar. Dieses Forschungsprojekt sucht nach einer neuen Variation dieser Darstellung, um die philosophischen Analogien beider Autoren aufzuspüren. Das erste Kapitel beschäftigt sich mit einer Erläuterung des Begriffes „umgedrehter Platonismus“, womit die Differenz zwischen diesen beiden Systemen definiert wird. Diese Diskrepanz ist spürbar in vier verschiedene Bereichen: metaphysisch, axiologisch, gnoseologisch und ästhetisch. Das zweite Kapitel behandelt die Rolle des Apollinischen und des Dionysischen in der nietzscheschen Theorie. Die beiden Konzepte werden mit dem des platonischen Eros verglichen, da diese es dem Menschen ermöglichen, die sinnliche Welt zu verlassen und eine Ur-Realität kennenzulernen. Das dritte Kapitel analysiert die Verurteilung der Kunst in Platon’s „Staat“. Der griechische Philosoph strebt die wahre Kenntnis an und verbindet seine ästhetischen Überlegungen mit der Idee der Wahrheit. Nietzsche bearbeitet diese Verbindung zwischen Ästhetik und Erkenntnistheorie unter dem Begriff »amor fati«. Das vierte Kapitel ist der Physiologie der Liebe gewidmet. Nietzsche verwandelt der Erkenntnisprozess in eine leidenschaftliche Liebe. Die Erkenntnis nimmt die Form einer Passion an und kristallisiert sich allmählich und nach einem langen Prozess mit Höhen und Tiefen in »amor fati«. »Amor fati« schafft eine Ästhetisierung der Erkenntnis und Epistemologiesierung der Ästhetik. Somit liegt Nietzsches Erkenntnistheorie parallel zu jener Platons.By claiming that his philosophy should be understood as “inverted Platonism” Nietzsche defined his relationship to the Platonic system. This research project aims to articulate a new understanding of this relationship by analyzing philosophical similarities between the two authors'' respective philosophies. The first chapter is dedicated to the explanation of the term “inverted Platonism” and articulates the differences between Plato''s and Nietzsche''s systems. These discrepancies are manifested in four main areas: the metaphysical, the axiological, the gnosiological and the aesthetic. The second chapter deals with the roles of the Apollonian and the Dionysian in Nietzschean theory. Both concepts are compared with the Platonic Eros, as they invite man to abandon the sensual world and instead to commune with the very origin of reality. The third chapter analyzes Plato´s denunciation of art in “The Republic”. The Greek philosopher seeks true knowledge and connects his aesthetic concerns with the idea of Truth. Nietzsche refers to the cynosure between aesthetics and cognitive theory as “amor fati”. The fourth chapter is dedicated to the physiology of love. Nietzsche transforms the cognitive process into a passionate love. Cognition assumes the shape of passion, slowly crystallizing over time, with many twists and turns, into “amor fati”. “Amor fati” aestheticizes cognition and epistemologizes aesthetics. Therefore Nietzsche''s cognitive theory is actually equivalent to that of Plato

Rethinking the Design of Ionic Conductors Using Meyer- Neldel- Conductivity Plot

From the discovery of the first fast ionic conductor silver iodide in the early 20th century to the recent discovery of lithium fast ionic conductors with ionic conductivities surpassing those of liquid electrolytes, high ionic conductivity Ï has often been associated with low activation energy Ea following the Arrhenius equation. However, the Meyer- Neldel rule (MNR) indicates that the Ea and prefactor Ï 0 are correlated, suggesting the relation between the Ea and Ï is, in fact, complex. In this perspective, the use of the Meyer- Neldel- conductivity plot and a critical descriptor, Meyer- Neldel energy Î 0, to guide the search for fast ionic conductors is proposed. Reported lithium, sodium, and magnesium ionic conductors are categorized into three types, depending on the relative magnitude between the Î 0 and thermal energy (kBT) at the application temperature. The process by which Ï can be optimized by tuning Ea for these types of ionic conductors is elaborated. This principle can be widely applied to all ionic conductors that obey the MNR at any application temperature. Furthermore, a pressure- tuning approach to measure the Î 0 rapidly is developed. These findings establish a previously missing step for designing new ionic conductors with improved ionic conductivity.Decreased activation energy is not always beneficial for achieving high ionic conductivity. Instead, ionic conductors can be categorized into three different types according to the relative magnitude between Meyer- Neldel energy and the thermal energy at the application temperature. A refined design principle of ionic conductors is proposed, revealing how the activation energy should be tuned for the optimized ionic conductivity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/167546/1/aenm202100325.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167546/2/aenm202100325-sup-0001-SuppMat.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/167546/3/aenm202100325_am.pd

Role of Point Defects in Spinel Mg Chalcogenide Conductors

10.1021/acs.chemmater.7b02909CHEMISTRY OF MATERIALS29229657-966

Design and Characterization of Host Frameworks for Facile Magnesium Transport

10.1146/annurev-matsci-081420-041617Annual Review of Materials Research52

Layered-to-Rock-Salt Transformation in Desodiated Na_<i>x</i>CrO₂ (<i>x</i> 0.4)

O3 layered sodium transition metal oxides (i.e., NaMO₂, M = Ti, V, Cr, Mn, Fe, Co, Ni) are a promising class of cathode materials for Na-ion battery applications. These materials, however, all suffer from severe capacity decay when the extraction of Na exceeds certain capacity limits. Understanding the causes of this capacity decay is critical to unlocking the potential of these materials for battery applications. In this work, we investigate the structural origins of capacity decay for one of the compounds in this class, NaCrO₂. The (de)­sodiation processes of NaCrO₂ were studied both <i>in situ</i> and <i>ex situ</i> through X-ray and electron diffraction measurements. We demonstrate that Na_<i>x</i>CrO₂ (0 < <i>x</i> < 1) remains in the layered structural framework without Cr migration up to a composition of Na_0.4CrO₂. Further removal of Na beyond this composition triggers a layered-to-rock-salt transformation, which converts P′3-Na_0.4CrO₂ into the rock-salt CrO₂ phase. This structural transformation proceeds via the formation of an intermediate O3 Na_δCrO₂ phase that contains Cr in both Na and Cr slabs and shares very similar lattice dimensions with those of rock-salt CrO₂. It is intriguing to note that intercalation of alkaline ions (i.e., Na⁺ and Li⁺) into the rock-salt CrO₂ and O3 Na_δCrO₂ structures is actually possible, albeit in a limited amount (∼0.2 per formula unit). When these results were analyzed under the context of electrochemistry data, it was apparent that preventing the layered-to-rock-salt transformation is crucial to improve the cyclability of NaCrO₂. Possible strategies for mitigating this detrimental phase transition are proposed