Enhancing the Stability of Non-Aqueous Electrolytes for Li-O<sub>2</sub> Batteries
Bibliographic record
Abstract
Li-O2 cells have been the subject of intense investigation in the last few years. The first step in the discharge reaction (oxygen reduction reaction or ORR) is thought to be a 1 e- process that forms the highly reactive intermediate superoxide, O2 -/LiO2. This superoxide species is responsible for the decomposition of most common non-aqueous electrolyte solvents.1 Finding a stable electrolyte for the non-aqueous Li-O2battery is a significant challenge. While allowing conduction of lithium ions between the electrodes, the electrolyte must be stable to nucleophilic attack on discharge, to oxidative decomposition on charge, and inert to the negative electrode. No such solution has been reported to date, and the understanding of the properties that confer stability is lacking. We will present a novel synthesized electrolyte, a chelate ionic liquid (IL), which is stable with respect to metallic lithium and also to superoxide-initiated attack. Figure 1a displays the 1H-NMR spectra of the by-products on cathodes discharged in the chelate IL as well as in the reference standard electrolyte, 1,2-dimethoxyethane (DME). Lithium formate (δ = 8.46 ppm) and dimethyl oxalate (δ = 3.92 ppm) are the two main proton-containing decomposition products formed from the DME molecule. These products are not observed for the new electrolyte. Moreover, when employed in a Li-O2 battery, 8-fold less CO2 evolution occurs on charge than for DME. CO2 is known to evolve during charge of the battery due to the oxidation of lithium carbonates/carboxylates which are formed as side-products by decomposition of electrolytes on discharge.2 This is shown by the results of differential electrochemical mass spectrometry (DEMS) in Figure 1b. Many other cell components besides the electrolyte suffer from instabilities in the non-aqueous Li-O2 battery, including binders and cathode materials.3,4 In particular, alternatives to carbon-based cathodes must be developed. By switching the positive electrode support to non-carbonaceous materials, cells utilizing the new chelate IL electrolyte have been cycled for over 300 hours with no capacity fading and little increase in polarization.5 In comparison, cells with the DME electrolyte, had a cycle life of less than 130 hours. This is displayed in Figure 2a and a comparison of the voltage profiles on the 10th cycle is shown in Figure 2b. The current causes of electrolyte instabilities will be discussed as well as pathways toward the development of new electrolyte/electrode systems with enhanced stabilities. References S. A. Freunberger, Y. Chen, N. E. Drewett, L. J. Hardwick, F. Bardé, P. G. Bruce, Angew. Chem. Int. Ed. 2011, 50, 1-6. B. D. McCloskey, A. Speidel, R. Scheffler, D. C. Miller, V. Viswanathan, J. S. Hummelshoj, J. K. Norskov, A. C. Luntz, J. Phys. Chem. Lett. 2012, 3, 997-1001. R. Black, S. H. Oh, J.-H. Lee, T. Yim, B. Adams, L. F. Nazar, J. Am. Chem. Soc. 2012, 134, 2902-2905. M. M. O. Thotiyl, S. A. Freunberger, Z. Peng, Y. Chen, Z. Liu, P. G. Bruce, Nature Mat. 2013 , 12, 1050-1056. B.D. Adams, R. Black, Z. Williams, R. Fernandes, M. Cuisinier, E. Jaemstorp Berg, P. Novak, G.K. Murphy, L.F. Nazar, Submitted.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.001 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".