| 1. |
- Chien, Yu-Chuan, 1990-
(författare)
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Operando Characterisation of Lithium–Sulfur Batteries
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Lithium–sulfur (Li–S) batteries have been under the spotlight of research on electrochemical energy storage systems, primarily owing to their high theoretical specific energy (2552 Wh kg-1). So far, Li–S cells on the market have presented a specific energy of 400 Wh kg-1, which is superior to many commercial alternatives, but far below the theoretical value. At the same time, Li–S batteries encounter other problems that are generally not associated with the standard Li-ion batteries, such as low utilisation rate of active materials and short cycle life. These often originate from the unique catholyte nature and/or the low reversibility of the metallic Li electrode.The dissolution and precipitation of elemental sulfur and lithium sulfide in the positive electrode are here investigated by operando X-ray diffraction (XRD) and small-angle neutron/X-ray scattering (SANS/SAXS) coupled with the Intermittent Current Interruption (ICI) method. The real-time internal and diffusion resistances are correlated to the kinetics of the precipitation of the crystalline species by operando XRD. Through operando SANS and SAXS, the formation of crystalline and amorphous solid-state discharge products and the compositional variation of catholyte inside the mesopores are linked to features in the resistance profiles. These studies indicate that the ionic transport limitation inside the positive electrode is the cause for the low sulfur utilisation during battery discharge.To examine the impact of the repetitive precipitation on the functionality of the positive sulfur electrode, a method based on electrochemical impedance spectroscopy (EIS) was developed to track the electrochemically active surface area of the carbon matrix in-situ over extensive cycling. The investigation found no progressive passivation on the positive electrode despite the rapid decrease in specific discharge capacity. Additionally, a novel three-electrode setup for Li–S cells reveals a faster growth of the resistance on the metallic Li electrode along cycling. These findings suggest that primarily the negative electrode limits the cycle life. Through providing the mechanistic insights of operational Li–S cells, this thesis demonstrates the value of simultaneous electrochemical and materials characterisations for understanding the complex Li–S system.
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| 2. |
- Finegan, Donal P, et al.
(författare)
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Quantifying Bulk Electrode Strain and Material Displacement within Lithium Batteries via High-Speed Operando Tomography and Digital Volume Correlation
- 2015
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Ingår i: Advanced Science. - : Wiley. - 2198-3844.
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Tidskriftsartikel (refereegranskat)abstract
- Tracking the dynamic morphology of active materials during operation of lithium batteries is essential for identifying causes of performance loss. Digital volume correlation (DVC) is applied to high-speed operando synchrotron X-ray computed tomography of a commercial Li/MnO2 primary battery during discharge. Real-time electrode material displacement is captured in 3D allowing degradation mechanisms such as delamination of the electrode from the current collector and electrode crack formation to be identified. Continuum DVC of consecutive images during discharge is used to quantify local displacements and strains in 3D throughout discharge, facilitating tracking of the progression of swelling due to lithiation within the electrode material in a commercial, spiral-wound battery during normal operation. Displacement of the rigid current collector and cell materials contribute to severe electrode detachment and crack formation during discharge, which is monitored by a separate DVC approach. Use of time-lapse X-ray computed tomography coupled with DVC is thus demonstrated as an effective diagnostic technique to identify causes of performance loss within commercial lithium batteries; this novel approach is expected to guide the development of more effective commercial cell designs.
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| 3. |
- Finegan, Donal P., et al.
(författare)
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Spatial dynamics of lithiation and lithium plating during high-rate operation of graphite electrodes
- 2020
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Ingår i: Energy and Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 13:8, s. 2570-2584
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Tidskriftsartikel (refereegranskat)abstract
- The principal inhibitor of fast charging lithium ion cells is the graphite negative electrode, where favorable conditions for lithium plating occur at high charge rates, causing accelerated degradation and safety concerns. The local response of graphite, both at the electrode and particle level, when exposed to fast charging conditions of around 6C is not well understood. Consequently, the conditions that lead to the onset of lithium plating, as well as the local dynamics of lithium plating and stripping, have also remained elusive. Here, we use high-speed (100 Hz) pencil-beam X-ray diffraction to repeatedly raster along the depth of a 101 µm thick graphite electrode in 3 µm steps during fast (up to 6C) charge and discharge conditions. Consecutive depth profiles from separator to current collector were each captured in 0.5 seconds, giving an unprecedented spatial and temporal description of the state of the electrode and graphite's staging dynamics during high rate conditions. The electrode is preferentially activated near the separator, and the non-uniformity increases with rate and is influenced by free-energy barriers between graphite's lithiation stages. The onset of lithium plating and stripping was quantified, occurring only within the first 15 µm from the separator. The presence of lithium plating changed the behavior of the underlying graphite, such as causing co-existence of LiC6 and graphite in the fully discharged state. Finally, the staging behavior of graphite at different rates was quantified, revealing a high dependency on rate and drastic hysteresis between lithiation and delithiation.
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| 4. |
- Owen, Rhodri E., et al.
(författare)
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Operando Ultrasonic Monitoring of Lithium-Ion Battery Temperature and Behaviour at Different Cycling Rates and under Drive Cycle Conditions
- 2022
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 169:4
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Tidskriftsartikel (refereegranskat)abstract
- Effective diagnostic techniques for Li-ion batteries are vital to ensure that they operate in the required voltage and temperature window to prevent premature degradation and failure. Ultrasonic analysis has been gaining significant attention as a low cost, fast, non-destructive, operando technique for assessing the state-of-charge and state-of-health of Li-ion batteries. Thus far, the majority of studies have focused on a single C-rate at relatively low charge and discharge currents, and as such the relationship between the changing acoustic signal and C-rate is not well understood. In this work, the effect of cell temperature on the acoustic signal is studied and shown to have a strong correlation with the signal's time-of-flight. This correlation allows for the cell temperature to be inferred using ultrasound and to compensate for these effects to accurately predict the state-of-charge regardless of the C-rate at which the cell is being cycled. Ultrasonic state-of-charge monitoring of a cell during a drive cycle illustrates the suitability of this technique to be applied in real-world situations, an important step in the implementation of this technique in battery management systems with the potential to improve pack safety, performance, and efficiency:
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| 5. |
- Ribadeneyra, Maria, et al.
(författare)
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Lignin-derived electrospun freestanding carbons as alternative electrodes for redox flow batteries
- 2020
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Ingår i: Carbon. - : Elsevier Ltd. - 0008-6223 .- 1873-3891. ; 157, s. 847-856
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Tidskriftsartikel (refereegranskat)abstract
- Redox flow batteries represent a remarkable alternative for grid-scale energy storage. They commonly employ carbon felts or carbon papers, which suffer from low activity towards the redox reactions involved, leading to poor performance. Here we propose the use of electrospun freestanding carbon materials derived from lignin as alternative sustainable electrodes for all-vanadium flow batteries. The lignin-derived carbon electrospun mats exhibited a higher activity towards the VO2 +/VO2+ reaction than commercial carbon papers when tested in a three-electrode electrochemical cell (or half-cell), which we attribute to the higher surface area and higher amount of oxygen functional groups at the surface. The electrospun carbon electrodes also showed performance comparable to commercial carbon papers, when tested in a full cell configuration. The modification of the surface chemistry with the addition of phosphorous produced different effect in both samples, which needs further investigation. This work demonstrates for the first time the application of sustainably produced electrospun lignin-derived carbon electrodes in a redox flow cell, with comparable performance to commercial materials and establishes the great potential of biomass-derived carbons in energy devices.
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| 6. |
- Robinson, James B., et al.
(författare)
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Identifying Defects in Li-Ion Cells Using Ultrasound Acoustic Measurements
- 2020
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 0013-4651 .- 1945-7111. ; 167:12
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Tidskriftsartikel (refereegranskat)abstract
- Identification of the state-of-health (SoH) of Li-ion cells is a vital tool to protect operating battery packs against accelerated degradation and failure. This is becoming increasingly important as the energy and power densities demanded by batteries and the economic costs of packs increase. Here, ultrasonic time-of-flight analysis is performed to demonstrate the technique as a tool for the identification of a range of defects and SoH in Li-ion cells. Analysis of large, purpose-built defects across multiple length scales is performed in pouch cells. The technique is then demonstrated to detect a microscale defect in a commercial cell, which is validated by examining the acoustic transmission signal through the cell. The location and scale of the defects are confirmed using X-ray computed tomography, which also provides information pertaining to the layered structure of the cells. The demonstration of this technique as a methodology for obtaining direct, non-destructive, depth-resolved measurements of the condition of electrode layers highlights the potential application of acoustic methods in real-time diagnostics for SoH monitoring and manufacturing processes.
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| 7. |
- Schlee, Philipp, et al.
(författare)
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Free-standing supercapacitors from kraft lignin nanofibers with remarkable volumetric energy density
- 2019
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6539. ; 10:10, s. 2980-2988
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Tidskriftsartikel (refereegranskat)abstract
- We have discovered a very simple method to address the challenge associated with the low volumetric energy density of free-standing carbon nanofiber electrodes for supercapacitors by electrospinning Kraft lignin in the presence of an oxidizing salt (NaNO3) and subsequent carbonization in a reducing atmosphere. The presence of the oxidative salt decreases the diameter of the resulting carbon nanofibers doubling their packing density from 0.51 to 1.03 mg cm−2 and hence doubling the volumetric energy density. At the same time, the oxidative NaNO3 salt eletrospun and carbonized together with lignin dissolved in NaOH acts as a template to increase the microporosity, thus contributing to a good gravimetric energy density. By simply adjusting the process parameters (amount of oxidizing/reducing agent), the gravimetric and volumetric energy density of the resulting lignin free-standing carbon nanofiber electrodes can be carefully tailored to fit specific power to energy demands. The areal capacitance increased from 147 mF cm−2 in the absence of NaNO3 to 350 mF cm−2 with NaNO3 translating into a volumetric energy density increase from 949 μW h cm−3 without NaNO3 to 2245 μW h cm−3 with NaNO3. Meanwhile, the gravimetric capacitance also increased from 151 F g−1 without to 192 F g−1 with NaNO3.
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| 8. |
- Taiwo, Oluwadamilola O., et al.
(författare)
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In-Situ Examination of Microstructural Changes within a Lithium-Ion Battery Electrode Using Synchrotron X-ray Microtomography
- 2015
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Ingår i: ECS Transactions. - : The Electrochemical Society. - 1938-6737 .- 1938-5862. ; 69:18, s. 81-85
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Konferensbidrag (refereegranskat)abstract
- In this work, we use synchrotron X-ray microtomographic imaging to examine in-situ changes in a silicon / lithium half-cell before and after lithiation. We visualize volume expansion within the silicon electrode matrix and active particle fracturing as a result of the lithiation process. A change in volume fraction of silicon with respect to electrode state-of-charge was also characterized.
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| 9. |
- Taiwo, Oluwadamilola O., et al.
(författare)
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Investigating the evolving microstructure of lithium metal electrodes in 3D using X-ray computed tomography
- 2017
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 19:33, s. 22111-22120
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Tidskriftsartikel (refereegranskat)abstract
- The growth of electrodeposited lithium microstructures on metallic lithium electrodes has prevented their use in rechargeable lithium batteries due to early performance degradation and safety implications. Understanding the evolution of lithium microstructures during battery operation is crucial for the development of an effective and safe rechargeable lithium-metal battery. This study employs both synchrotron and laboratory X-ray computed tomography to investigate the morphological evolution of the surface of metallic lithium electrodes during a single cell discharge and over numerous cycles, respectively. The formation of surface pits and the growth of mossy lithium deposits through the separator layer are characterised in three-dimensions. This has provided insight into the microstructural evolution of lithium-metal electrodes during rechargeable battery operation, and further understanding of the importance of separator architecture in mitigating lithium dendrite growth.
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| 10. |
- Taiwo, Oluwadamilola O., et al.
(författare)
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Microstructural degradation of silicon electrodes during lithiation observed via operando X-ray tomographic imaging
- 2017
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Ingår i: Journal of Power Sources. - : Elsevier BV. - 0378-7753. ; 342, s. 904-912
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Tidskriftsartikel (refereegranskat)abstract
- Due to their high theoretical capacity compared to that of state-of-the-art graphite-based electrodes, silicon electrodes have gained much research focus for use in the development of next generation lithium-ion batteries. However, a major drawback of silicon as an electrode material is that it suffers from particle fracturing due to huge volume expansion during electrochemical cycling, thus limiting commercialization of such electrodes. Understanding the role of material microstructure in electrode degradation will be instrumental in the design of stable silicon electrodes. Here, we demonstrate the application of synchrotron-based X-ray tomographic microscopy to capture and track microstructural evolution, phase transformation and fracturing within a silicon-based electrode during electrochemical lithiation.
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