| 1. |
- Koriukina, Tatiana, 1994-
(författare)
-
Titanium-Based Negative Electrode Materials for Rechargeable Batteries : In Search of the Redox Reactions
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rechargeable batteries, particularly, lithium-ion batteries (LIBs) have proven to be stable and reliable energy storage devices over the past few decades. The rapid demands regarding battery applications and the pressure to move away from the fossil fuel era drive the search for new materials for better rechargeable batteries for electric vehicles, renewable energy storage, and portable electronics. In this context a deeper understanding of the electrochemical processes governing the electrochemical behaviour of batteries is required. This thesis work investigates the use of two titanium-based materials as negative electrode materials for lithium- and sodium-ion batteries. The focus is on identifying the redox reactions responsible for the electrochemical capacities observed for the materials. Having knowledge of the available redox reactions for new materials used in batteries is crucial in predicting whether they can compete with existing battery chemistries and be commercially viable.One part of this thesis work examines the electrochemical behaviuor of a 2D titanium carbide, Ti3C2Tx, a member of the MXene family, in lithium- and sodium-ion batteries. The other part explores an A-site cation deficient Li0.18Sr0.66Ti0.5Nb0.5O3 (L018STN) perovskite oxide, known for its high lithium-ion conductivity, in LIBs. The electrodes were electrochemically evaluated in pouch-cell batteries and analysed post hoc by means of X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. The results indicate that only the surface Ti(I), Ti(II), Ti(III), and Ti(IV) titanium species of the Ti3C2Tx flakes participate in the redox reactions and give rise to the electrochemical capacity. Furthermore, the restacking of individual flakes within the bulk of the Ti3C2Tx electrode limits the electroactive surface of a freestanding Ti3C2Tx electrode that is available for the redox reactions. The reversible capacities of Ti3C2Tx electrodes can be improved by long-term cycling (an effect known as capacity activation) and heat treatment, as the surface titanium species gradually oxidise to higher oxidation states, e.g., Ti(III) and Ti(IV), or transform to titanium oxides TixOy. The results for L018STN electrodes show that both titanium and niobium are redox active on over-lithiation, that is, when more than one Li+ was inserted per a vacant A-site. The structural reorganization during over-lithiation enabled access to diffusion paths for fast lithium-ion diffusion even when a high concentration of lithium was inserted into the structure. The findings of this thesis work thus indicate that a portion of the Ti3C2Tx electrode is electrochemically inactive when subjected to electrochemical cycling. This can be ascribed to its structure and two-dimensional nature. As a result, Ti3C2Tx cannot outperform existing negative electrodes for lithium- or sodium-ion batteries. The results obtained for L018STN provide valuable information on the lithium-ion diffusion behaviours in A-site cation deficient perovskite oxides. In a broader sense, this thesis work emphasises the significance of employing a multi-technique approach to obtain a good understanding of the underlying redox mechanisms when analysing battery materials.
|
|
| 2. |
- Kotronia, Antonia
(författare)
-
Probing Critical Interfaces in Dual-Ion Batteries : The Road Towards Performant Graphite Cathodes
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transitioning into a zero-emission society will require massive efforts with respect to the harnessing and storage of renewable energy resources. The development of large-scale, electrochemical energy storage systems based on abundant and environmentally benign compounds is seen upon as a key factor for guaranteeing a successful outcome. On these grounds, research into post lithium-ion battery technologies has become increasingly important. Among emerging concepts is that of dual-ion batteries (DIBs); the operational mechanism of which uses both the cation and anion in the electrolyte. DIBs offer some unique advantages compared to other cell chemistries, owing to the unconventional materials combinations they enable. Graphite versus graphite cells constitute a cell chemistry which results in high average voltage (> 4.5 V), decent specific capacity (~100 mAh g-1) and which eliminates transition metals from the cathode. Despite considerable merits, graphite versus graphite dual-ion cells have proven difficult to realize, mainly due to the instability of the cathode electrolyte interface (CEI) at high potentials. This thesis explores critical interfaces in both Li- and K-based DIBs and considers strategies to mitigate these instabilities, based on a combination of electrode and electrolyte engineering. The influence of the electrolyte salt and solvent on the CEI is studied through electrochemical characterization methods and X-ray photoelectron spectroscopy (XPS). Conventional LiPF6-based electrolytes are contrasted to formulations using high concentrations of lithium imide salts such as lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The impact of incorporating functional additives and precycling protocols to reduce electrochemical irreversibility is discussed for Li4Ti5O12‑graphite and MoS2-graphite cells tailored for Li- and K-based DIBs, respectively. In addition, a ternary ionogel is introduced as a novel electrolyte platform for DIBs due to its promising ionic conductivity, oxidative stability and mechanical properties. Finally, the impact of different electrode binders on the surface chemistry and electrochemical performance of the graphite cathode is elucidated. In summary, this work indicated that a passivating, anion conducting CEI is key to enabling dual-ion batteries. Despite the cumbersome nature of this task, ways forward were highlighted both in terms of concrete examples, such as the construction of DIBs incorporating functional additives (e.g. triallyl phosphate) and binders (e.g. poly(vinylidene fluoride-co-hexafluoropropylene)), and in terms of methodology, including the design of reliable cycling protocols to evaluate DIB-performance.
|
|
| 3. |
- Cuevas Zuviría, Ignacio Andrés
(författare)
-
The complexity of ceramic-based electrolytes for all-solid-state batteries
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present energy and mobility transformation, heavily relying on Electric Vehicles (EVs) and renewable energy sources, needs batteries. Lithium-ion batteries are the main candidates for reshaping our transport system. Despite already dominating the energy storage components of the EV market, Li-ion batteries possess safety issues related to their flammable liquid electrolytes. Moreover, they get close to reaching their maximum energy density. Alternative battery technologies, safer and able to store more energy, therefore gather great interest. One prominent example is solid-state batteries, employing ceramic or polymeric electrolytes, and their composites.This thesis explores in-house processing and characterisation techniques to study the processes in, and improve the performance of, inorganic electrolytes for all solid-state lithium batteries. Inorganic electrolytes are solids with high ionic conductivities, which can enable safe batteries with high power and energy densities. There are, however, many challenges to overcome before they can reach commercialization. Advancements are associated with understanding the properties that control the ionic transport.One focus of this thesis is treating the electrolyte material Li7La3Zr2O12 (LLZO) with boric acid. Such surface treatment appears to tackle the formation of detrimental Li2CO3, and is therefore explored for both sintered ceramic electrolyte pellets and LLZO powders. Respectively, this strategy is evaluated both by analysing the effect upon sintering, and when implementing the powders in a polymer electrolyte matrix. In contact with the acid, LLZO forms a LiBO2 layer with beneficial effects on conductivity. For LLZO powders, the acid treatment yielded solids with promising grain coalescences upon sintering. When incorporated into polymer electrolyte, the higher ionic conductivity suggests a beneficial role of the LiBO2 layer for the polymer-ceramic contacts.Another promising inorganic electrolyte is Li1+xAlxTi2-x(PO4)3 (LATP), whose easy processing and high conductivity are shadowed by its instability vs. lithium metal. As a strategy to protect the LATP material, it has here been inserted into different polymer electrolyte matrices. While the composites generally displayed poor synergistic effects between the materials, some promising results were seen for polyesters, not least high transference numbers.In summary, these results provide a step forward into understanding how a functional all-state battery could be built using ceramic electrolytes, and the importance of tailoring the surfaces – both in ceramic and composite electrolytes.
|
|
| 4. |
- Källquist, Ida
(författare)
-
Combining Electrochemistry and Photoelectron Spectroscopy for the Study of Li-ion Batteries
- 2021
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis photoelectron spectroscopy (PES) is combined with electrochemistry to investigate the electrochemical processes that occur at the electrode/electrolyte interfaces in lithium-ion batteries (LIBs). LIB systems are studied by the use of both ex situ PES, where electrodes are electrochemically pre-cycled and subsequently measured by PES, and operando PES, where electrodes are cycled during PES measurements. Ex situ PES is used to determine the main degradation mechanisms of a novel high capacity material, Li2VO2F. The capacity fade seen for Li2VO2F. is found to be related to an irreversible oxidation of the active material at high voltages, and a continuous surface layer formation at low voltages. To decrease the capacity fading three strategies for optimizing the interface are investigated. The results show that a surface coating of AlF3 most efficiently can mitigate electrolyte reduction, while boron containing electrolyte additives and transition metal substitution more successfully limit the oxidation of the active material. A large part of the work performed in this thesis has been devoted towards developing a methodology suitable for conducting operando ambient pressure photoelectron spectroscopy (APPES) measurements on LIB systems. A general connection between the theory of PES and electrochemistry is made, where in particular a model suitable for interpreting operando APPES results on solid/liquid interfaces is suggested. The model is further developed for the specific case of LIB interfaces. The results from the operando studies show that the kinetic energy shifts of the liquid electrolyte measured by APPES can be correlated to the electrochemical reactions occurring at the interface. If no charge transfer occurs, the kinetic energy shift is proportional to the applied voltage. During charge transfer the behavior is more complex, and the kinetic energy shifts are related to the change in chemical potential of the working electrode. In summary, this thesis exemplifies how both ex situ and operando PES are highly useful techniques for the study of LIB battery interfaces. The possibilities of both techniques are highlighted, and important considerations for an accurate interpretation of the PES results are also discussed.
|
|
