1,2‐Dimethoxyethane Degradation Thermodynamics in Li−O₂ Redox Environments

Abstract

The reaction thermodynamics of the 1,2-dimethoxyethane (DME), a model solvent molecule commonly used in electrolytes for Li-O rechargeable batteries, has been studied by first-principles methods to predict its degradation processes in highly oxidizing environments. In particular, the reactivity of DME towards the superoxide anion O in oxygen-poor or oxygen-rich environments is studied by density functional calculations. Solvation effects are considered by employing a self-consistent reaction field in a continuum solvation model. The degradation of DME occurs through competitive thermodynamically driven reaction paths that end with the formation of partially oxidized final products such as formaldehyde and methoxyethene in oxygen-poor environments and methyl oxalate, methyl formate, 1-formate methyl acetate, methoxy ethanoic methanoic anhydride, and ethylene glycol diformate in oxygen-rich environments. This chemical reactivity indirectly behaves as an electroactive parasitic process and therefore wastes part of the charge exchanged in Li-O cells upon discharge. This study is the first complete rationale to be reported about the degradation chemistry of DME due to direct interaction with O /O molecules. These findings pave the way for a rational development of new solvent molecules for Li-O electrolytes.

Degradation of LiTfO/TEGME and LiTfO/DME Electrolytes in Li-O2Batteries

“…Apparently our findings confirm their results with a different technique also in the case of the LiTfO/DME and LiTfO/TEGDME electrolytes. One may also recall that the accumulation of carboxylate and carbonate organic by-products originated by the degradation of ether solvents agrees with chemical degradation model outlined by us in a previous publication, 22 based on computational thermodynamic predictions.…”

“…This prediction updates and strengthen the general DME degradation reaction schemes suggested by us in the Ref. 22 that identifies dimethyl oxalate, methyl formate, 1-formate methyl acetate, methoxy ethanoic methanoic anhydride, and ethylene glycol diformate as final degradation products. On passing it is interesting to underline that the formation of these products is in nice agreement with the here discussed XPS results.…”

“…21,35. The onset degradation reaction of the DME molecule in Li-O 2 cells.-As already mentioned the reaction products observed by XPS for both DME and TEGDME electrolytes (see the Figure 5) nicely match with the chemical reaction model developed by us for the degradation of DME in Ref. 22 based on DFT thermodynamic predictions and with the previous one proposed by Nazar et al 8 We predicted a complex degradation mechanism driven by the extremely favorable thermodynamics of the formation of formates/acetates/carbonates and anhydrides through the chemical oxidation of the DME molecules by molecular oxygen and superoxide anion. Our model assumed as onset reaction the homolytic H-abstraction from the ether molecule due to a nucleophilic attack from superoxide anions.…”

“…In the Ref. 22 our choice was made in consideration of the general literature consensus. 7,60,71 In fact, although the C-H bond cleavage can follow different reaction paths (i.e.…”

Synergistic Electro-Catalysis of Pd/PdO Nanoparticles and Cr(III)-Doped NiCo2O4 Nanofibers in Aprotic Li-O2 Batteries

“…LiO 2 is a very strong nucleophilic radical molecule 7 and it is an unavoidable intermediate in ORR (O 2 +Li + +e − →LiO 2 ). 1,11 Once formed LiO 2 may: (a-b) dimerize/decompose by releasing Li 2 O 2 and O 2 (either in the (a) singlet or (b) triplet states); 11,54 (c) be further reduced 1 to give Li 2 O 2 ; (d) attack the solvent molecules to give HLiO 2 and organic alkyl radicals.…”