| 1. |
- Østli, Elise R. R., et al.
(author)
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Stabilizing the Cathode Interphase of LNMO using an Ionic-liquid based Electrolyte
- 2023
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In: Batteries & Supercaps. - : John Wiley & Sons. - 2566-6223. ; 6:7
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Journal article (peer-reviewed)abstract
- The ionic liquid (IL)-based electrolyte comprising 1.2 M lithium bis(fluorosulfonyl)imide (LiFSI) in N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR13FSI) (ILE) has been evaluated as a suitable system for the high-voltage cathode material LiNi0.5-xMn1.5+xO4 (LNMO) when cycled vs. graphite anodes. The oxidative stability of the ILE was evaluated by linear sweep voltammetry (LSV) and synthetic charge-discharge profile voltammetry (SCPV) and was found to exceed that of state-of-the-art 1 M LiPF6 in 1 : 1 ethylene carbonate (EC) : diethylcarbonate (DEC) (LP40). Improved cycling performance both at 20 degrees C and 45 degrees C was found for LNMO||graphite full cells with the IL electrolyte. X-ray photoelectron spectroscopy (XPS) analysis showed that robust and predominantly inorganic surface layers were formed on the LNMO cathode using the ILE, which stabilized the electrode. Although the high viscosity of the ILE limits the rate performance at 20 degrees C, this ILE is a promising alternative electrolyte for use in lithium-ion batteries (LiBs) with high-voltage cathodes such as LNMO, especially for use at elevated temperatures.
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| 2. |
- Ostli, Elise R., et al.
(author)
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Limitations of Ultrathin Al2O3 Coatings on LNMO Cathodes
- 2021
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In: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 6:45, s. 30644-30655
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Journal article (peer-reviewed)abstract
- This study demonstrates the application of Al2O3 coatings for the high-voltage cathode material LiNi0.5–xMn1.5+xO4−δ (LNMO) by atomic layer deposition. The ultrathin and uniform coatings (0.6–1.7 nm) were deposited on LNMO particles and characterized by scanning transmission electron microscopy, inductively coupled plasma mass spectrometry, and X-ray photoelectron spectroscopy. Galvanostatic charge discharge cycling in half cells revealed, in contrast to many published studies, that even coatings of a thickness of 1 nm were detrimental to the cycling performance of LNMO. The complete coverage of the LNMO particles by the Al2O3 coating can form a Li-ion diffusion barrier, which leads to high overpotentials and reduced reversible capacity. Several reports on Al2O3-coated LNMO using alternative coating methods, which would lead to a less homogeneous coating, revealed the superior electrochemical properties of the Al2O3-coated LNMO, suggesting that complete coverage of the particles might in fact be a disadvantage. We show that transition metal ion dissolution during prolonged cycling at 50 °C is not hindered by the coating, resulting in Ni and Mn deposits on the Li counter electrode. The Al2O3-coated LNMO particles showed severe signs of pitting dissolution, which may be attributed to HF attack caused by side reactions between the electrolyte and the Al2O3 coating, which can lead to additional HF formation. The pitting dissolution was most severe for the thickest coating (1.7 nm). The uniform coating coverage may lead to non-uniform conduction paths for Li, where the active sites are more susceptible to HF attack. Few benefits of applications of very thin, uniform, and amorphous Al2O3 coatings could thus be verified, and the coating is not offering long-term protection from HF attack.
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| 3. |
- Østli, Elise R., et al.
(author)
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On the Durability of Protective Titania Coatings on High‐Voltage Spinel Cathodes
- 2022
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In: ChemSusChem. - : John Wiley & Sons. - 1864-5631 .- 1864-564X. ; 15:12
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Journal article (peer-reviewed)abstract
- TiO2-coating of LiNi0.5-xMn1.5+xO4 (LNMO) by atomic layer deposition (ALD) has been studied as a strategy to stabilize the cathode/electrolyte interface and mitigate transition metal (TM) ion dissolution. The TiO2 coatings were found to be uniform, with thicknesses estimated to 0.2, 0.3, and 0.6 nm for the LNMO powders exposed to 5, 10, and 20 ALD cycles, respectively. While electrochemical characterization in half-cells revealed little to no improvement in the capacity retention neither at 20 nor at 50 °C, improved capacity retention and coulombic efficiencies were demonstrated for the TiO2-coated LNMO in LNMO||graphite full-cells at 20 °C. This improvement in cycling stability could partly be attributed to thinner cathode electrolyte interphase on the TiO2-coated samples. Additionally, energy-dispersive X-ray spectroscopy revealed a thinner solid electrolyte interphase on the graphite electrode cycled against TiO2-coated LNMO, indicating retardation of TM dissolution by the TiO2-coating.
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