Alkyl Dicarbonate-Based Electrolytes Can Enable Long-Lived Li-Ion Cells at High-Temperatures
Notice bibliographique
Résumé
Alkyl dicarbonates are known electrolyte degradation products produced in Li-ion cells that use ethylene carbonate (EC) and dimethyl carbonate (DMC) as electrolyte components. Also referred to as dimerization compounds, dimethyl 2,5-dioxahexanedioate (DMOHC) and diethyl 2,5-dioxahexanedioate (DEOHC), were investigated as a possible sole electrolyte solvent or and one component of a blended solvent mixture, when mixed with linear carbonates. The viscosities of DMOHC and DEOHC were measured in this report and compared to the predictions of the Advanced Electrolyte Model1, along with the two alkyl dicarbonates mixed with lithium salts and other common electrolyte solvents. Electrolytes based on DMOHC or DEOHC alone exhibit much higher viscosity than conventional EC-based electrolytes at room temperature. Thus, for testing, LiNi0.5Mn0.3Co0.2O2/graphite (NMC532), LiNi0. 83Mn0. 6Co0. 11O2/graphite (Ni83) and LiFePO4(LFP)/graphite cells with DMOHC were tested at 70°C and 85°C using C/20 charge and discharge rates. DMOHC and DEOHC were mixed with two different electrolyte salts. First, the common LiPF6 salt and the second, lithium bis(fluorosulfonyl)imide (LiFSI), both with 2% vinylene carbonate (VC). These two electrolytes were tested in NMC532/graphite cells cycled to 4.3V at a C/20 charge/discharge rate and 70°C. Cells with DMOHC and LiFSI showed considerable improvements in capacity retention compared to those filled with an EC-based electrolyte with LiPF6 salt, also cycled at 70°C. The same conclusion was found with NMC532 cells filled with DEOHC with LiFSI salt or LiPF6. Figure 1a shows the fractional capacity versus time for NMC532/graphite, Ni83/graphite and LFP/graphite pouch cells with 1.0 M LiFSI in DMOHC with 2% VC (vinylene carbonate) and 1% DTD (ethylene sulfate) additives tested at C/20 and 85°C. These cells were tested to upper cut-off potentials of 3.8, 3.9 and 3.65 V respectively. In addition, Figure 1b shows the corresponding voltage polarization results. Results show that Ni-containing cells experience exceptional lifetimes and low impedance growth despite the high cycling temperature. DMOHC-containing cells have since been tested up to 100°C. DMOHC was most advantageous for mitigating severe gassing at high temperatures. Ex-situ gas experiments show DMOHC-containing Ni83 cells produce the least amount of gas even at high voltage (4.0 V) compared to cells using EC-based electrolytes. Ni-containing cells operating to low voltage limits show unprecedented cycling lifetimes when using DMOHC electrolytes containing LIFSI while also exhibiting limited gassing. To mitigate the high viscosity of DMOHC, various cells were filled with electrolytes that used DMOHC and various percentages of diethyl carbonate (DEC) and dimethyl carbonate (DMC) with LiFSI as the salt. DMC/DEC was chosen for its low viscosity and its ionic conductivity. Even with DMC, the cycling performance showed improvements over traditional EC-based electrolytes. There were slight decreases in performance compared to a cell with a pure DMOHC electrolyte. In addition, various additives were tested, including prop-1-ene-1,3-sultone (PES), to see if gassing could be further limited. We propose DMOHC and DEOHC as new solvents for Li-ion cell electrolytes, possibly replacing EC, to enable long-lasting, high-temperature tolerant Li-ion cells. REFERENCES E. R. Logan, E. M. Tonita, K. L. Gering, and J. R. Dahn, J Electrochem Soc, 165, A3350–A3359 (2018). Figure 1. (a) Normalized capacity versus time for LFP (blue), NMC532 (red) and Ni83 (black) artificial graphite cells, using 1M LIFSI DMOHC 2%VC 1%DTD electrolyte cycling at C/20 and at 85°C. (b) corresponding voltage polarization data versus time. Figure 1
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Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,001 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».