| Author: | Fan, Ke |
| Title: | Theoretical investigation of two-dimensional materials as promising electrode materials for Li-ion and Li-S batteries |
| Advisors: | Huang, Haitao (AP) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Lithium cells Two-dimensional materials Electrodes Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Physics |
| Pages: | xxvi, 174 pages : color illustrations |
| Language: | English |
| Abstract: | Lithium-based batteries have attracted high attention in the field of energy storage because of the high theoretical energy density (weight and volume) of lithium metal. Among them, lithium-ion (Li-ion) and lithium-sulfur (Li-S) batteries have made great progress in the past few decades. However, the real-operation properties still cannot satisfy the requirements for practical large-scale commercial applications and most batteries contain toxic substances. Therefore, the research and preparation of new electrode materials with higher energy density, lower cost, and higher safety still face major challenges. Two-dimensional (2D) materials, due to their large basal plane area, in principle, can provide more active sites for atoms adsorption, and therefore represent promising candidates among many types of electrode materials. At present, a series of 2D materials have been designed and used as electrode materials for batteries, however, the electrochemical reaction process or mechanism occurring inside has not been fully proved and further optimization strategies have not been systematically proposed. With the significant improvement in computing power, the first-principles calculation method based on density functional theory (DFT) is regarded as an effective tool to understand the electrochemical reaction process at an atomic scale. Therefore, providing a nano-scale perspective to grasp the structure-property correlation and to help deal with the current electrode design challenges. This dissertation uses a first-principles method to design novel 2D electrode materials for Li-ions and Li-S batteries, systematically studies the experimental feasibility, electronic properties, storage and diffusion mechanism of the designed electrode material, and explores the possible limiting factors of the 2D electrode material in the reaction process. Several works related to the electrode design are carried out as follows: (1) 2D MXenes, because of the high electronic conductivity, have been treated as promising candidates for electrode materials. By comparing V3C2 MXene as the anode in metal-ion (Li, Na, K, and Ca) batteries by means of DFT computations, the V3C2 monolayer exhibits a low diffusion barrier and high storage capacity for Li and Na atoms. Thus, V3C2 monolayers are predicted to be promising anode materials for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). (2) Because of the quasi-planar structure, 2D PCx (x = 2, 5, and 6) systems may provide abundant adsorption sites for practical battery applications. Our calculations further reveal that the theoretical specific capacity of monolayer PC5 and PC6 can reach up to 1251.7 and 1235.9 mA h g-1, respectively. These results suggest that both PC5 and PC6 monolayers are promising anode materials for LIBs. (3) A class of self-intercalation 2D materials, namely "ic-2Ds", were demonstrated can be synthesized by experiments. Seven 3d transition intercalated materials with the content of σ=33% have been studied as promising anode materials in LIBs. Among them, Ti7S12 is demonstrated to have a relatively higher capacity and smaller diffusion energy barrier, therefore, suggesting as promising anode material for LIBs. (4) By discussing the thermodynamic and kinetic suppression of polysulfide shuttling, the nitride MXenes as hosts for Li-S batteries are systematically studied. Both the bare and functionalized V2NT2 (T = O, F, OH, and S) exhibit metallicity, but only functionalized V2NT2 (T = O, F, and S) possess moderate lithium polysulfides (LiPSs) adsorption strength, which thermodynamically benefits the suppression of the dissolution and shuttling of LiPSs. Moreover, the surface functionalized V2NT2 also exhibit outstanding catalytic ability for Li2S decomposition during charge, which decrease the energy barrier from 3.64 eV (bare V2N) to 1.15 (V2NO2) and 1.19 eV (V2NS2), and increase the charging kinetics. In summary, we focused on the applications of ab initio simulations to design the high-performance 2D electrode materials in Li-ion and Li-S batteries. The core philosophy is to understand the intrinsic properties of battery materials and the electrochemical reaction mechanism, covering the ground state structure, diffusion barrier, and capacity of 2D materials. With the development of advanced theoretical and experimental techniques, we believe that batteries with high energy density and long-term cycle stability will be realized in the near future. |
| Rights: | All rights reserved |
| Access: | open access |
Copyright Undertaking
As a bona fide Library user, I declare that:
- I will abide by the rules and legal ordinances governing copyright regarding the use of the Database.
- I will use the Database for the purpose of my research or private study only and not for circulation or further reproduction or any other purpose.
- I agree to indemnify and hold the University harmless from and against any loss, damage, cost, liability or expenses arising from copyright infringement or unauthorized usage.
By downloading any item(s) listed above, you acknowledge that you have read and understood the copyright undertaking as stated above, and agree to be bound by all of its terms.
Please use this identifier to cite or link to this item:
https://theses.lib.polyu.edu.hk/handle/200/11777