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- Brant, William R., et al.
(författare)
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Local structure transformations promoting high lithium diffusion in defect perovskite type structures
- 2023
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Ingår i: Electrochimica Acta. - : Elsevier. - 0013-4686 .- 1873-3859. ; 441
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Tidskriftsartikel (refereegranskat)abstract
- Defect perovskites, AxBO3 such as (Li3xLa2/3-x)TiO3, are attracting attention as high capacity electrodes in lithium-ion batteries. However, the mechanism enabling high lithium storage capacities has not been fully investigated. In this work, the reversible insertion and removal of lithium up to an average A-site cavity occupancy of 1.71 in the defect perovskite (Li0.18Sr0.66)(Ti0.5Nb0.5)O3 is investigated. It was shown that subtle lithium reorganization during lithiation has a significant impact on enabling high capacity. Contrary to previous studies, lithium was coordinated to triangular faces of Ti/Nb oxygen octahedra and offset from O4 windows between A-site cavities in the as-synthesised material. Upon electrochemical lithiation Li-Li repulsion redistributes of all the lithium towards the O4 window position resulting in a loss of lithium mobility. Surprisingly, the mobility is regained during over-lithiation and following multiple electrochemical cycles. It is suggested that lithium reorganisation into the center of the O4 window alleviates the Li-Li repulsion and modifies the diffusion behavior from site percolation to bond percolation. The results obtained provide valuable insight into the chemical drivers enabling higher capacities and enhanced diffusion in defect perovskites. More broadly the study delivers fundamental understanding on the non-equilibrium structural transformations occurring within electrode materials during repeated electrochemical cycles.
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| 2. |
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| 3. |
- Koriukina, Tatiana, 1994-, et al.
(författare)
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On the Use of Ti3C2TX MXene as a Negative Electrode Material for Lithium-Ion Batteries
- 2022
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Ingår i: ACS Omega. - : American Chemical Society (ACS). - 2470-1343. ; 7:45, s. 41696-41710
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Tidskriftsartikel (refereegranskat)abstract
- The pursuit of new and better battery materials has given rise to numerous studies of the possibilities to use two-dimensional negative electrode materials, such as MXenes, in lithium-ion batteries. Nevertheless, both the origin of the capacity and the reasons for significant variations in the capacity seen for different MXene electrodes still remain unclear, even for the most studied MXene: Ti3C2Tx. Herein, freestanding Ti3C2Tx MXene films, composed only of Ti3C2Tx MXene flakes, are studied as additive-free negative lithium-ion battery electrodes, employing lithium metal half-cells and a combination of chronopotentiometry, cyclic voltammetry, X-ray photoelectron spectroscopy, hard X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy experiments. The aim of this study is to identify the redox reactions responsible for the observed reversible and irreversible capacities of Ti3C2Tx- based lithium-ion batteries as well as the reasons for the significant capacity variation seen in the literature. The results demonstrate that the reversible capacity mainly stems from redox reactions involving the Tx-Ti-C titanium species situated on the surfaces of the MXene flakes, whereas the Ti-C titanium present in the core of the flakes remains electro-inactive. While a relatively low reversible capacity is obtained for electrodes composed of pristine Ti3C2Tx MXene flakes, significantly higher capacities are seen after having exposed the flakes to water and air prior to the manufacturing of the electrodes. This is ascribed to a change in the titanium oxidation state at the surfaces of the MXene flakes, resulting in increased concentrations of Ti(II), Ti(III), and Ti(IV) in the Tx-Ti-C surface species. The significant irreversible capacity seen in the first cycles is mainly attributed to the presence of residual water in the Ti3C2Tx electrodes. As the capacities of Ti3C2Tx MXene negative electrodes depend on the concentration of Ti(II), Ti(III), and Ti(IV) in the Tx-Ti-C surface species and the water content, different capacities can be expected when using different manufacturing, pretreatment, and drying procedures.
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| 4. |
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| 5. |
- Koriukina, Tatiana, 1994-
(författare)
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Titanium-Based Negative Electrode Materials for Rechargeable Batteries : In Search of the Redox Reactions
- 2023
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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.
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