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Elucidating Non-aqueous Solvent Stability and Associated Decomposition Mechanisms for Mg Energy Storage Applications From First-Principles.

ABSTRACT: 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 (Mg²⁺ ? 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.

SUBMITTER: Seguin TJ

PROVIDER: S-EPMC6465547 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Elucidating Non-aqueous Solvent Stability and Associated Decomposition Mechanisms for Mg Energy Storage Applications From First-Principles.

Seguin Trevor J TJ Hahn Nathan T NT Zavadil Kevin R KR Persson Kristin A KA

Frontiers in chemistry 20190409

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., tetrame ...[more]

PMID: 31024883

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Project description:High performance organogel polyelectrolytes were synthesized by super acid catalyst step-growth polycondensation of isatin and the non-activated multiring aromatic p-terphenyl. Subsequently, a chemical modification reaction was carried out to obtained quaternary ammonium functionalized polyelectrolytes through a nucleophilic substitution reaction with (3-bromopropyl)trimethylammonium bromide and potassium carbonate at room temperature. Different functionalization degrees were obtained by controlling the molar ratio of the polymer and the modification agent. The organogel polyelectrolytes were formed due to the high phase segregation and self-assembling observed owing to the amphiphilic character of the material (hydrophobic backbone and hydrophilic fragment grafted). The organogel polyelectrolytes were used to fabricate supercapacitors using two commercial graphite electrodes. These polyelectrolytes displayed good ionic conductivity without the use of another doping agent such as salts, acids or ionic liquids. In this work, a strong correlation of functionalization degree and ionic conductivity of the polyelectrolytes and capacitance of the supercapacitors was observed. The ionic conductivity of the polyelectrolytes reached 0.46 mS cm-1 for the 100% functionalization degree, meanwhile the polyelectrolyte with the 10% functionalization degree shows 0.036 mS cm-1. Li-doped polyelectrolytes showed higher ionic conductivity due the presence of extra ionic charges (2.26 and 0.2 mS cm-1 for the polyelectrolytes with the 100% and 10% of functionalization degree, respectively). The principal novelty of this work lies in the possibility of modulating the ionic conductivity of organogels and the capacitance of supercapacitors by chemical modifications. The capacitance of the supercapacitors was 1.17 mF cm-2 for the 100% functionalized polyelectrolyte and is higher in comparison with the polyelectrolyte with 10% functionalization degree (0.68 mF cm-2) measured at a discharge current of 52 μA cm-2 by galvanostatic charge discharge technique. Additionally, when lithium salt (lithium triflate) was added, the polyelectrolytes retained a gel consistency, increasing the ionic conductivity and capacitance. For the doped polyelectrolytes, the areal capacitance reaches 1.37 mF cm-2 for the 100% functionalization degree polyelectrolyte with lithium triflate. These organogel polyelectrolytes open the possibility to design flexible and all solid-state supercapacitors without the risk of leakage.

Dataset Information

Elucidating Non-aqueous Solvent Stability and Associated Decomposition Mechanisms for Mg Energy Storage Applications From First-Principles.

Publications

Elucidating Non-aqueous Solvent Stability and Associated Decomposition Mechanisms for Mg Energy Storage Applications From First-Principles.

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