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Elucidating non-aqueous solvent stability and associated decomposition mechanisms for mg energy storage applications from first-principles

Frontiers in Chemistry

Seguin, Trevor J.; Hahn, Nathan T.; Zavadil, Kevin R.; Persson, Kristin A.

Rational design of novel electrolytes with enhanced functionality requires fundamental molecular-level understanding of structure-property relationships. Here we examine the suitability of a range of organic solvents for non-aqueous electrolytes in secondary magnesium batteries using density functional theory (DFT) calculations as well as experimental probes such as cyclic voltammetry and Raman spectroscopy. The solvents considered include ethereal solvents (e.g., glymes) sulfones (e.g., tetramethylene sulfone), and acetonitrile. Computed reduction potentials show that all solvents considered are stable against reduction by Mg metal. Additional computations were carried out to assess the stability of solvents in contact with partially reduced Mg cations (Mg 2+ → Mg + ) formed during cycling (e.g., deposition) by identifying reaction profiles of decomposition pathways. Most solvents, including some proposed for secondary Mg energy storage applications, exhibit decomposition pathways that are surprisingly exergonic. Interestingly, the stability of these solvents is largely dictated by magnitude of the kinetic barrier to decomposition. This insight should be valuable toward rational design of improved Mg electrolytes.

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TYPE Journal Article YEAR 2019
ScopusOSTIDOI

Directly Formed Alucone on Lithium Metal for High-Performance Li Batteries and Li-S Batteries with High Sulfur Mass Loading

ACS Applied Materials and Interfaces

Chen, Lin; Huang, Zhennan; Shahbazian-Yassar, Reza; Libera, Joseph A.; Klavetter, Kyle C.; Zavadil, Kevin R.; Elam, Jeffrey W.

Lithium metal is considered the "holy grail" of next-generation battery anodes. However, severe parasitic reactions at the lithium-electrolyte interface deplete the liquid electrolyte and the uncontrolled formation of high surface area and dendritic lithium during cycling causes rapid capacity fading and battery failure. Engineering a dendrite-free lithium metal anode is therefore critical for the development of long-life batteries using lithium anodes. In this study, we deposit a conformal, organic/inorganic hybrid coating, for the first time, directly on lithium metal using molecular layer deposition (MLD) to alleviate these problems. This hybrid organic/inorganic film with high cross-linking structure can stabilize lithium against dendrite growth and minimize side reactions, as indicated by scanning electron microscopy. We discovered that the alucone coating yielded several times longer cycle life at high current rates compared to the uncoated lithium and achieved a steady Coulombic efficiency of 99.5%, demonstrating that the highly cross-linking structured material with great mechanical properties and good flexibility can effectively suppress dendrite formation. The protected Li was further evaluated in lithium-sulfur (Li-S) batteries with a high sulfur mass loading of ∼5 mg/cm2. After 140 cycles at a high current rate of ∼1 mA/cm2, alucone-coated Li-S batteries delivered a capacity of 657.7 mAh/g, 39.5% better than that of a bare lithium-sulfur battery. These findings suggest that flexible coating with high cross-linking structure by MLD is effective to enable lithium protection and offers a very promising avenue for improved performance in the real applications of Li-S batteries.

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TYPE Journal Article YEAR 2018
ScopusOSTIDOI

Instability at the electrode/electrolyte interface induced by hard cation chelation and nucleophilic attack

Chemistry of Materials

Yu, Yi; Baskin, Artem; Valero-Vidal, Carlos; Hahn, Nathan H.; Liu, Qiang; Zavadil, Kevin R.; Eichhorn, Bryan W.; Prendergast, David; Crumlin, Ethan J.

Electrochemistry is necessarily a science of interfacial processes, and understanding electrode/electrolyte interfaces is essential to controlling electrochemical performance and stability. Undesirable interfacial interactions hinder discovery and development of rational materials combinations. By example, we examine an electrolyte, magnesium(II) bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) dissolved in diglyme, next to the Mg metal anode, which is purported to have a wide window of electrochemical stability. However, even in the absence of any bias, using in situ tender X-ray photoelectron spectroscopy, we discovered an intrinsic interfacial chemical instability of both the solvent and salt, further explained using first-principles calculations as driven by Mg2+ dication chelation and nucleophilic attack by hydroxide ions. The proposed mechanism appears general to the chemistry near or on metal surfaces in hygroscopic environments with chelation of hard cations and indicates possible synthetic strategies to overcome chemical instability within this class of electrolytes.

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TYPE Journal Article YEAR 2017
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Results 26–50 of 198
Results 26–50 of 198