Two dimensional naxsis as a promising anode material for rechargeable sodium based batteries ab initio material design

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY - PHAM THI DUNG TWO-DIMENSIONAL NaxSiS AS A PROMISING ANODE MATERIAL FOR RECHARGEABLE SODIUM-BASED BATTERIES: AB INITIO MATERIAL DESIGN MASTER'S THESIS Hanoi, 2018 VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY PHAM THI DUNG TWO-DIMENSIONAL NaxSiS AS A PROMISING ANODE MATERIAL FOR RECHARGEABLE SODIUM-BASED BATTERIES: AB INITIO MATERIAL DESIGN MAJOR: NANO TECHNOLOGY SUPERVISOR: Dr DINH VAN AN Hanoi, 2018 ACKNOWLEDGMENT I am truly honored to submit my master thesis for the degree of Master at Nanotechnology Program, Vietnam Japan University This work has been carried out in the Nanotechnology program, Vietnam Japan University, Vietnam National University of Hanoi I would like to express my sincere thạnks to my supervisor: Dr Dinh Van An, JICA expert, lecturer, Vietnam Japan University (VJU), Vietnam National University (VNU) for accepting me as his student, for guidance, and his encouragement to complete this research I would like to thank all students and teachers of Nanotechnology, Vietnam Japan University, Vietnam National University of Hanoi for the pleasant and stimulating atmosphere during my research study Hanoi, May 25, 2018 Student Pham Thi Dung i TABLE OF CONTENTS ACKNOWLEDGMENT i TABLE OF CONTENTS ii LIST OF FIGURES iv LIST OF TABLES v LIST OF ABBREVIATIONS vi INTRODUCTION CHAPTER LITERATURE REVIEW 1.1 Energy demand 1.2 Rechargeable batteries 1.3 Electrode materials 1.3.1 Cathode material 1.3.2 Anode material 1.3.2.1 Silicene, germane, stanene, phosphorene and borophene 1.3.2.2 2D transition metal oxides 1.3.2.3 2D transition metal dichalcogenides 10 1.3.2.4 2D transition metal carbides/nitrides 11 1.3.2.5 Emerging 2D materials 11 1.4 Purpose of thesis 12 CHAPTER METHOD 13 2.1 Density functional theory 13 2.1.1 Hohenberg - Kohn theorems 15 2.1.2 Exchange-Correlation Functionals 17 2.1.3 Solving Kohn-Sham Equation 18 2.2 Nudged Elastic Band method 18 2.3 Calculation Scheme 20 CHAPTER RESULTS AND DISCUSSION 21 3.1 Atomic structure of NaxSiS (x= 0-0.5) 21 3.1.1 Host material SiS (x=0) 21 ii 3.1.2 Na1Si18S18 (x=0.05) 22 3.1.3 Higher Na concentration NaxSiS (x= 0.111-0.5) 24 3.2 Theoretical capacity and open circuit voltage 28 3.2.1 Theoretical capacity 28 3.2.2 Open circuit voltage 28 3.3 Adsorption energy 29 3.4 Electronic structure 31 3.5 Diffusion mechanism of sodium on the surface of NaxSiS 36 CONCLUSION 39 REFERENCES 40 iii LIST OF FIGURES Page Figure 1.1 Schematic operation of batteries Figure 2.1 An illustration of the self-consistent field 18 Figure 2.2 Decomposition of force in an image 19 Figure 3.1 The optimized structure of silicene sulfide The blue and yellow balls represent for Silicon and Sulfur atoms, respectively 21 Figure 3.2 Adsorption area of Na 23 Figure 3.3 Symmetrical adsorption sites of Na ion 24 Figure 3.4 Possible adsorption sites of the second Na ion 25 Figure 3.5 Possible configurations of Na0.167SiS 26 Figure 3.6 The most stable structures of different sodium concentrations (x=0.050.5) 27 Figure 3.7 The adsorption energy diagram 30 Figure 3.8 The density of state of pristine SiS Fermi level is set at zero 32 Figure 3.9 The density of state of Na0.05SiS Fermi level is set at zero 33 Figure 3.10 The density of state of Na0.111SiS Fermi level is set at zero 34 Figure 3.11 The density of state of Na0.278SiS Fermi level is set at zero 35 Figure 3.12 Diffusion pathway of sodium along a-direction 37 Figure 3.13 Diffusion pathways of sodium along b-direction 37 Figure 3.14 The diffusion pathway of single Na atom on SiS surface 38 iv LIST OF TABLES Page Table 1.1 Sodium and Lithium characteristics Table 3.1 The optimized structure parameter of silicene sulfide 22 Table 3.3 The sodium adsorption energies (Adsorption energy is in units of eV per number of Na atoms) 29 v LIST OF ABBREVIATIONS 2D: Two-dimensional DFT: Density functional theory DOS: Density of State EES: Electrical energy storage GGA: Generalized Gradient Approximation LDA: Local density approximation LIBs: Lithium-ion batteries OCV: Open circuit voltage PAW: Projector augmented-wave SES: Stationary energy storage SIBs: Sodium ion battery VASP: Vienna ab initio Simulation Package NEB: Nudged Elastic Band method vi INTRODUCTION Nowadays, energy security is the goal of many countries, including Vietnam The shortage of energy, the effective use of recycling energy, and environmental pollution are emergency problems that demand strong efforts of scientists and governments In general, energy comes from two sources: nonrenewable source (fossil carbon such as oil, coal, and gas) and renewable source (wind, water, sun) The excessive exploitation of fossil energy leads to serious environmental problems such as pollution, global warming, and ozone depletion Therefore, the use of renewable energy is promoted to study and apply in the world, this essential solution is likely to deal with the lack of energy issue However, the efficient storage of renewable energy is the big challenge because almost renewable resources are intermittent sources Therefore, the study of efficient energy storage devices is extremely necessary The various electricity storage devices were designed such as batteries, capacitors, and the other devices Unlike primary batteries, secondary batteries are more popular for their charge and discharge abilities in use The performance of rechargeable batteries is determined by theoretical capacity, voltage, electric conductivity, and life cycle parameters, strongly depends on electrodes and electrolyte materials Therefore, the investigations to find out suitable materials for batteries have attracted much attention by both experiment and computational science Today, thanks to the improvement in computational technology, researchers are making vigorous progress in the understanding of materials at atomic and molecular levels With this understanding, we can select suitable materials for specific purposes and also improve advanced materials for applications Aiming at enhancing the collaboration between experimental research and simulation work in studying on existing, and new materials as well as their application, computational material science with its techniques is applied to solve material relating problems Moreover, computational experiments have an advantage over real experiments because most of the variables can be controlled in experiment processes Nanotechnology may gradually take the forefront of scientists in the computational material science due to their nanoscale for several decades At electronic level, density functional theory (DFT) is a popular method to investigate material characteristics in quantum physics Regarding the requirement of stable storage electric devices and the demand of understanding material properties, we have investigated the performance of twodimensional (2D) material as a promising anode for rechargeable batteries by simulation methods In this research, electronic properties and stable structures of new materials Na-silicene sulfide were systematically investigated as a promising anode for rechargeable sodium-ion batteries Figure 3.8 The density of state of pristine SiS Fermi level is set at zero 32 Figure 3.9 The density of state of Na0.05SiS Fermi level is set at zero 33 Figure 3.10 The density of state of Na0.111SiS Fermi level is set at zero 34 Figure 3.11 The density of state of Na0.278SiS Fermi level is set at zero 35 3.5 Diffusion mechanism of sodium on the surface of NaxSiS The ionic conductivity is one of the key factors determining the power of battery To determine ionic conductivity, it is necessary to explore diffusion mechanism Therefore, diffusion barrier is the important parameter determining the effective performance of battery material Herein, the diffusion mechanism is explored by using NEB method When a Na atom diffuses in SiS surface, it tends to jump to the next most stable sites Five images are optimized between two continuously stable positions (C sites) As mentioned in the previous discussion, two elementary processes, including along a- and b-direction are considered to explore the diffusion mechanism The first pathway is along the a-direction (intrahexagonal) with a distance of 2.6 It is found that the sodium diffusion on SiS with the barrier of 0.070 eV along the a-direction, the sodium atom migrates from C site to H site and then to the next C site in the same octagonal Si6S2 (Figure 3.12) The value of activation energy is the energy difference between C and H configurations The second pathway is along b-direction with the diffusion distance of 2.9 Å, the single Na atom transfer from a C site to another C site in the next octagonal Si6S2 along b-direction or inter-hexagonal (Figure3.13) The activation energy is calculated of 183 36 Figure 3.12 Diffusion pathway of sodium along a-direction Figure 3.13 Diffusion pathways of sodium along b-direction In sodium migration process, sodium can move follow both of pathways The Na atoms can diffuse along the only b-direction as the red line or in the combination of two elementary processes as the green line, which is illustrated in Figure 3.14 37 Figure 3.14 The diffusion pathway of single Na atom on SiS surface Therefore, the sodium barrier energy of SiS material is determined of 0.183 , which is much smaller than that in LIBs (0.43 ) [49] It means that the performance of SiS for SIBs is more effective than for LIBs Furthermore, the sodium migration kinetic is faster than various 2D materials, such as: MoS2 (280680 ) [14], BP (217 ) [60], and TiS2 (220 38 ) [44] CONCLUSION To sum up, we have investigated the performance of a new material Na xSiS as a promising anode material The stable Na adsorption positions were explored by using Computational DFT-based Nanoscope [58] for the single adsorption, and found for various inserting sodium Crystal and electronic structures of the most stable configurations were investigated The electronic structure, open circuit voltage and capacity for the one-side adsorption of SiS were also calculated The diffusion mechanism of Na ions was also investigated by using NEB method It is found that silicene sulfide has an adsorption energy to Na atom about of , which is large enough to ensure the stability of Na inserted SiS during intercalation/deintercalation process The electronic structure, open circuit voltage and capacity of SiS were also calculated The electronic structure of pristine SiS monolayer and Na adsorbed SiS show the distinction of a semiconductor material with band gap of 0.99 The fully intercalated phase Na0.5SiS is corresponding to a highest theoretical capacity of 187.42 mAh/g per one side layer, which is higher than that in LixSiS (167 , Li0.375SiS), MoS2 (146 ), and BP (143 ) Secondly, the diffusion mechanism of Na ions was also investigated by using NEB method Two possible elementary diffusion processes were explored, including along a- and b-direction Most importantly, Silicene sulfide shows a good sodium mobility with the energy barrier along two dimension is 183 meV, which is much smaller than that in LixSiS issue (430 MoS2 (280-680 ), 2D TiS2 (220 ),and 2D ) Our investigations also reveal that SiS exhibits better electrochemical performance as an anode in the SIBs than in the LIBs From these findings, it can be suggested that 2D SiS could be a promising anode material for sodium batteries 39 REFERENCES [1] J Conti, P Holtberg, J Diefenderfer, A LaRose, J T Turnure, L Westfall, International Energy Outlook 2016 With Projections to 2040 2016, USDOE Energy Information Administration (EIA), Washington, DC (United States) Office of Energy Analysis [2] H Chen, T N Cong, W Yang, C Tan, Y Li, Y Ding (2009) "Progress in electrical energy storage system: A critical review" Progress in Natural Science, Vol 19, Iss 3, pp 291-312 [3] R Kempener, G de Vivero (2015), Renewables and electricity storage: A technology roadmap for REmap 2030, Vol 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