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- Carvalho, Rodrigo P.
(författare)
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Organic Electrode Battery Materials : A Journey from Quantum Mechanics to Artificial Intelligence
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Batteries have become an irreplaceable technology in human life as society becomes progressively more dependent on electricity. The demand for novel battery technologies has increased fast, especially with the popularisation of different portable devices. However, the current battery industry relies heavily on non-renewable resources that are also prone to provoke environmental harm. Among the possible candidates for the next generation of batteries, organic electroactive materials (OEMs) have become attractive due to a series of advantages: vastly accessible from renewable raw materials; highly versatile due to the possible functionalisation mechanisms; possibly lower production costs; reduced environmental impacts; etc. Nevertheless, some drawbacks need to be overcome before OEMs become competitive. Issues with energy density, rate capability and cycling stability hinder their final technological application. This thesis thereby discusses fundamental aspects of OEMs and proposes novel techniques to accelerate the materials discovery process.The first part of this thesis presents a pathway to systematically investigate organic materials by combining quantum mechanics calculations and crystal structure predictions. An evolutionary algorithm predicts the crystal structure of several OEMs, enabling an initial assessment of the electronic structure and the thermodynamics of the ionic insertion mechanism in these compounds. Furthermore, this first part also suggests an approach to tailor OEMs, identifying their charge storage limits and the possible occurrence of metastable phases during the ion insertion process. However, the presented strategy, while accurate, is seriously limited by its high computational demands, which are unrealistic for high-throughput screening of novel materials.Since organic materials represent a possibly limitless universe of compounds, alternative techniques are needed. Thus, the second part of this thesis combines quantum mechanics and artificial intelligence (AI), rendering a powerful platform to aid this task. An “AI-\textit{kernel}” was employed to analyse millions of organic compounds, discovering novel possible organic battery materials. Moreover, the AI accurately identified common functional groups associated with higher-voltage electrodes and suggested features that may aid future materials design. Furthermore, the kernel can also identify materials suitable for Na- and K-ion batteries and anticipate their redox stability.In conclusion, this thesis has focused on investigating fundamental properties of organic electroactive materials, particularly the ionic insertion process in batteries. Furthermore, AI-driven methodologies have also been proposed, accurately evaluating OEMs and enabling fast access to the gigantic organic realm when searching for novel battery electrode materials.
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| 2. |
- Chen, Xin, 1992-
(författare)
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Theoretical Investigations of Two-Dimensional Materials : Studies on Electronic, Magnetic, Mechanical, and Thermal Properties
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two-dimensional (2D) materials have been paid enormous attention since the first realization of graphene in 2004, in connection to high-speed flexible electronics, 2D magnetism, optoelectronics, and so on. Apart from graphene, many new 2D materials with special properties have been predicted and synthesized. For the understanding of several interesting phenomena and prediction of new 2D materials, materials-specific density functional theory (DFT) plays a very important role.In this thesis, based on first-principles calculations, structural, magnetic, electronic, mechanical, and thermal transport properties of two kinds of 2D systems are investigated.The first kind of 2D materials is based on the synthesized material or the predicted structure with ultralow energy. These materials were functionalized by adsorbing transition metal atoms or oxygen atoms, which makes a significant difference in the properties. A part of the thesis covers the study of the self-assembly process of 3d transition metal hexamers on graphene with different defects. Interestingly, it is found that the easy axis of magnetization can be tuned between in-plane and out-of-plane directions in the presence of an external electric field. The second subsection is the oxygen functionalized form of 2D honeycomb and zigzag dumbbell silicene. Interestingly, both the structures are Dirac semimetal.The other kind of 2D materials discussed in this thesis are new materials which were never reported before. Starting from a global structure search, we predicted several structures with ultrahigh stability and novel properties. One work is about a new allotrope of graphene, namely PAI-graphene. It is a new structural motif, which is energetically very close to graphene with interesting properties. PAI-graphene is a semimetal with distorted Dirac cones. By applying tensile strain, three different topological phases can be achieved. The second subsection is the work about new 2D structural forms of A2B (A=Cu, Ag, Au, and B=S, Se). Our obtained square-A2B (s-A2B) structures are energetically more favored than all the reported 2D structures for A2B. s-A2B structures are direct bandgap semiconductors with high carrier mobilities. All the s-A2B structures have unusually low lattice thermal conductivities. Moreover, s-A2B monolayers have ultra-low Young’s moduli and in-plane negative Poisson’s ratios. The third work is about the phase transition in s-A2B monolayers. We proposed two new s-A2B structure, s(I)- and s(II)-Au2Te. S(I)-Au2Te is an auxetic direct-gap semiconductor, while s(II)-Au2Te is a topological insulator. By applying strain or using thermal means, we can achieve a structural phase transition between the two phases.
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