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- Chen, Heyin, et al.
(författare)
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Investigating Surface Reactivity of a Ni-Rich Cathode Material toward CO2, H2O, and O2 Using Ambient Pressure X-ray Photoelectron Spectroscopy
- 2023
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:22, s. 11458-11467
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Tidskriftsartikel (refereegranskat)abstract
- Layered Ni-rich transition metal oxide materials are considered the most promising cathodes for use in commercial Li-ion batteries. Due to their instability in air, an impurity layer forms during storage under ambient conditions, and this layer increases electrochemical polarization during charging and discharging, which ultimately leads to a lower cycling capacity. In this work, we found that storage of the LiNi0.8Mn0.1Co0.1O2 (NMC 811) material in ultrahigh vacuum (UHV) can restore the surface by reducing the amount of native carbonate species in the impurity layer. In this work, in situ soft X-ray ambient pressure photoelectron spectroscopy is used to directly follow the interaction between common gases found in air and the NMC 811 surface. During gas exposure of the NMC 811 surface to pure CO2, O2, and a mixture of both pure gases, surface-adsorbed CO2 or/and O2 were detected; however, permanent changes could not be identified under UHV after the gas exposure. In contrast, a permanent increase in metal hydroxide species was observed on the sample surface following H2O vapor exposure, and an increased intensity in the carboxylate peak was observed after exposure to a mixture of CO2/O2/H2O. Thus, the irreversible degradation reaction with CO2 is triggered in the presence of H2O (on relevant time scales defined by the experiment). Additional measurements revealed that X-ray irradiation induces the formation of metal carbonate species on the NMC 811 surface under CO2 and H2O vapor pressure.
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| 5. |
- Mikheenkova, Anastasiia, et al.
(författare)
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Ageing of High Energy Density Automotive Li-Ion Batteries : The Effect of Temperature and State-of-Charge
- 2023
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 170:8
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Tidskriftsartikel (refereegranskat)abstract
- Lithium ion batteries (LIB) have become a cornerstone of the shift to electric transportation. In an attempt to decrease the production load and prolong battery life, understanding different degradation mechanisms in state-of-the-art LIBs is essential. Here, we analyze how operational temperature and state-of-charge (SoC) range in cycling influence the ageing of automotive grade 21700 batteries, extracted from a Tesla 3 long Range 2018 battery pack with positive electrode containing LiNixCoyAlzO2 (NCA) and negative electrode containing SiOx-C. In the given study we use a combination of electrochemical and material analysis to understand degradation sources in the cell. Herein we show that loss of lithium inventory is the main degradation mode in the cells, with loss of material on the negative electrode as there is a significant contributor when cycled in the low SoC range. Degradation of NCA dominates at elevated temperatures with combination of cycling to high SoC (beyond 50%).
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| 6. |
- Mikheenkova, Anastasiia, et al.
(författare)
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Ageing of High Energy Density Automotive Li-ion Batteries: The Effect of Temperature and State-of-Charge
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Lithium ion batteries (LIB) have become a cornerstone of the shift to electric transportation. In an attempt to decrease the production load and prolong battery life, understanding different degradation mechanisms in state-of-the-art LIBs is essential. Here, we analyze how operational temperature and state-of-charge (SoC) range in cycling influence the ageing of automotive grade 21700 batteries, extracted from a Tesla 3 Long Range 2018 battery pack with positive electrode containing LiNixCoyAlzO2 (NCA) and negative electrode containing SiOx-C. In the given study we use a combination of electrochemical and material analysis to understand degradation sources in the cell. Herein we show that loss of lithium inventory is the main degradation mode in the cells, with loss of material on the negative electrode as there is a significant contributor when cycled in the low SoC range. Degradation of NCA dominates at elevated temperatures with combination of cycling to high SoC (beyond 50%).
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| 7. |
- Mikheenkova, Anastasiia, 1995-
(författare)
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Investigating ageing mechanisms in electric vehicle batteries : A multiscale approach to material analysis
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Electrifying passenger transport is a key strategy in combating global warming, with Li-ion batteries (LIBs) being the current go-to technology. Despite LIB’s satisfactory performance and carbon-neutral operation, lifetime and safety are still public concerns. A thorough understanding of battery ageing is crucial for improving LIBs and advancing the overall sustainability of LIB technology. This thesis bridges a gap between academic and industrial research by combining commercial battery investigation with a multiscale approach using a combination of in-house and synchrotron characterization methods used with the implementation of method development to study commercial batteries.The multiple degradation mechanisms were identified at various scales in the aged commercial cells. Specifically, the results show that the studied cells exhibit significant and distinct ageing heterogeneity in prismatic and cylindrical cell formats, where the area with the highest degradation is found on the side of the positive tab, where the current and temperature gradients are expected to be the strongest. After decoupling the performance on the electrode level, the Ni-rich layered oxide positive electrodes show a significant increase in Li+ diffusion resistance in the aged materials as a function of the State of Charge (SoC) range and temperature. Furthermore, heterogeneity is an issue relevant also on a secondary particle scale, where identified SoC gradients ranging from the centre to the surface of the particle might induce kinetic limitations and cause an increase in Li+ diffusion resistance. On a single particle level, the formation of a large number of voids within the grains was found. Such degradation can additionally contribute to the resistance increase in the material by changing tortuosity for Li-ions. Finally, at the atomic level, Ni was found to be the dominant charge compensator, which can decrease up to 25% of the redox activity after ageing. Compared to Ni, Co was found to be less redox-active, but more involved in charge compensation through changes in hybridization with the oxygen atom. The oxygen, in turn, was revealed to participate in anionic redox reactions at low SoC by both hybridization to TM and also through the formation of molecular oxygen at lower potentials than previously reported. The observed decrease in oxygen anion redox activity follows with material losing performance.The results presented in the thesis demonstrate the importance of the multiscale approach in order to form a more complete understanding of the degradation processes which have effects within different scales.
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| 8. |
- Mikheenkova, Anastasiia, et al.
(författare)
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Resolving high potential structural deterioration in Ni-rich layered cathode materials for lithium-ion batteries operando
- 2023
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Ingår i: Journal of Energy Storage. - : Elsevier. - 2352-152X .- 2352-1538. ; 57
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Tidskriftsartikel (refereegranskat)abstract
- LixNi0.90Co0.05Al0.05O2 (NCA) extracted from an automotive battery cell is studied using a combination of in-house operando techniques to understand the correlation between gas evolution and structural collapse when NCA is cycled to high potentials in a lithium-ion battery configuration. The operando techniques comprise X-ray diffraction (XRD) and online electrochemical mass spectrometry (OEMS), and cycled using intermittent current interruption (ICI). The ICI cycling protocol is used to assess the dynamic change in resistance as well as to provide a validation of the operando setups. Both gas evolution and structural collapse have previously been observed as degradation mechanisms of Ni-rich electrodes including NCA, however, their causal link is still under debate. Here our presented results show a correlation between the decrease of the interlayer distance in NCA with both an increase in CO2 evolution and diffusion resistance above 4.1 V. Additionally, particle cracking, which is a mechanism often correlated with gas evolution, was found to be reversible and visible before gas evolution and Li diffusion resistance increase. The ICI technique is shown to be useful for the correlation of operando experiments on parallel setups and evaluation of mass transport dependent processes.
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| 10. |
- Mikheenkova, Anastasiia, et al.
(författare)
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The Role of Oxygen in Automotive Grade Lithium-Ion Battery Cathodes : An Atomistic Survey of Ageing
- 2024
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry. - 2050-7488 .- 2050-7496. ; 12:4, s. 2465-2478
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The rising demand for high-performance lithium-ion batteries, pivotal to electric transportation, hinges on key materials like the Ni-rich layered oxide LiNixCoyAlzO2 (NCA) used in cathodes. The present study investigates the redox mechanisms, with particular focus on the role of oxygen in commercial NCA electrodes, both fresh and aged under various conditions (aged cells have performed >900 cycles until a cathode capacity retention of ∼80%). Our findings reveal that oxygen participates in charge compensation during NCA delithiation, both through changes in transition metal (TM)–O bond hybridization and formation of partially reversible O2, the latter occurs already below 3.8 V vs. Li/Li+. Aged NCA material undergoes more significant changes in TM–O bond hybridization when cycling above 50% SoC, while reversible O2 formation is maintained. Nickel is found to be redox active throughout the entire delithiation and shows a more classical oxidation state change during cycling with smaller changes in the Ni–O hybridization. By contrast, Co redox activity relies on a stronger change in Co–O hybridization, with only smaller Co oxidation state changes. The Ni–O bond displays an almost twice as large change in its bond length on cycling as the Co–O bond. The Ni–O6 octahedra are similar in size to the Co–O6 octahedra in the delithiated state, but are larger in the lithiated state, a size difference that increases with battery ageing. These contrasting redox activities are reflected directly in structural changes. The NCA material exhibits the formation of nanopores upon ageing, and a possible connection to oxygen redox activity is discussed. The difference in interaction of Ni and Co with oxygen provides a key understanding of the mechanism and the electrochemical instability of Ni-rich layered transition metal oxide electrodes. Our research specifically highlights the significance of the role of oxygen in the electrochemical performance of electric-vehicle-grade NCA electrodes, offering important insights for the creation of next-generation long-lived lithium-ion batteries.
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