Multinuclear Solid-State NMR Studies of Cathode Materials for Lithium and Sodium Ion Batteries
Notice bibliographique
Résumé
Lithium ion batteries have long been promised as an alternative energy technology, owing to their high volumetric and gravimetric energy densities.1 The cathode (positive electrode) material is of particular importance as the choice of this component can dictate overall battery performance. Polyanionic structural frameworks such as phosphates or fluorosulfates are an attractive alternative to the traditional layered oxide cathode structures due to their high electrochemical and thermal stability.2 More recently, the reconsideration of sodium ion batteries has become popular, and while the larger, heavier, sodium ion decreases overall energy density for a given material vs. Li, the cost and abundance benefits are expected to largely outweigh this disadvantage.3 Despite considerable research efforts to improve cathode materials for both lithium and sodium ion batteries, the role of structure on ion mobility is not yet fully understood; a property integral to electrochemical success. Solid-state nuclear magnetic resonance (ssNMR) is a valuable tool for studying these polyanionic structures, as it is sensitive to both the mobile ion of interest (23Na or 6Li/7Li) as well as the surrounding structural framework (31P, 19F). The fluorophosphate family of sodium cathode materials is extremely promising, as the materials are both thermally and electrochemically stable, with the advantage of being relatively inexpensive depending on the redox active transition metal of choice. In particular, the electrochemical performance of Na2MPO4F (M= Fe, Co, Ni, Mn) has been investigated in recent years, and is found to be an exemplary candidate for use in Na ion batteries.4 We have utilized 23Na NMR to gain understanding of the structural changes that occur during electrochemical extraction and reinsertion of Na ions during the charging and discharging processes of a number of fluorophosphate analogues. The paramagnetic nature of many of these materials makes their investigation by NMR non-trivial, requiring the use of fast magic-angle spinning (MAS) and low external magnetic fields. In particular, the structural changes occurring upon desodiation of Na2FePO4F were investigated by NMR, where the attenuation of one of the two sites is attributed to the selective removal of Na ions from a single crystallographic position. Additionally, by cycling Na2FePO4F versus a Li-metal counter electrode we observe evidence of substantial Na-Li ion exchange by 7Li NMR, opening the door for interesting heteronuclear correlation experiments with a hybrid Na/Li cathode material. The movement of Li ions as a function of electrochemical cycling can also be tracked in Li cathode materials. Receiving significant attention is the fluorosulfate structure of the form LiFeSO4F, which benefits from a high redox potential and excellent electrochemical behaviour.5,6 6,7Li ssNMR was used here to identify any changes to the Li environment at various stages along the electrochemical charge/discharge cycle, providing valuable insight into the structural stability of this material. (1) Tarascon, J.-M.; Armand, M. Nature 2001. (2) Padhi, A. K.; Nanjundaswamy, K. S.; Masquelier, C.; Masque; Okada, S.; Goodenough, J. B. J. Electrochem. Soc. 1997, 144, 1609–1613. (3) Ellis, B. L.; Nazar, L. F. Current Opinion in Solid State & Materials Science 2012, 16, 168–177. (4) Ellis, B. L.; Makahnouk, W. R. M.; Rowan-Weetaluktuk, W. N.; Ryan, D. H.; Nazar, L. F. Chem. Mater. 2010, 22, 1059–1070. (5) Barpanda, P.; Ati, M.; Melot, B. C.; Rousse, G.; Chotard, J.-N.; Doublet, M.-L.; Sougrati, M. T.; Corr, S. A.; Jumas, J.-C.; Tarascon, J.-M. Nature Materials 2011, 10, 772–779. (6) Tripathi, R.; Gardiner, G. R.; Islam, M. S.; Nazar, L. F. Chem. Mater. 2011, 23, 2278–2284. Figure 1: 23Na 30 kHz MAS NMR spectra of pristine Na2FePO4F (red) and electrochemically generated Na1.5FePO4F (blue) demonstrating the decrease in intensity at site A during cycling as well as the formation of a novel site (#).
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Comment cette classification a été obtenuedéplier
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 | 0,001 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,001 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,001 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,001 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,001 |
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 ».