Theoretical Study on Interfacial Phenomena and Ion Transport in Energy Materials and Nanoparticles

Abstract

The increasing demands on clean renewable energy resources to mitigate climate change is causing a huge shift towards the usage of electricity as the main power source. This drives the development and advancement of energy storage systems. Nanomaterials provide various possibilities in addressing this issue since materials at nanoscale exhibit distinct and tunable phyico-chemical properties compared to its bulk properties. Despite significant advancement in experimental techniques and apparatus, it is still difficult to have a holistic understanding on atomistic level phenomena occurring at the surface or interfaces. To this end, theoretical study based on multiscale simulation comes into play. The fast-growing computational power adds on to the staggering opportunity to accurately predict and virtually observe ion transport mechanism, interfacial phenomena, and numerous physical and chemical properties. Particularly in this dissertation, we will discuss the interplay of ion transport and interfacial phenomena in current collector design for Li-ion battery, solid electrolyte for Zn-ion battery, electrolyte additives design for Li-ion battery, and nucleation phenomena in Ag nanoparticles (nanocrystals) by the mean of multiscale molecular simulation. In this dissertation, we first underlined the motivation behind our studies on energy materials and nanoparticles. The scope of the interfacial phenomena and ion transport in nanomaterials covered are mainly focused on thermodynamics parameters which can be used as guiding principle in energy applications. We further discussed on the multiscale molecular simulation method which we used as our experimental tools, namely density functional theory (DFT), Monte Carlo (MC), and molecular dynamics (MD) simulations. These tools allow us to probe quantum level up to molecular level phenomena and dynamics. In the second chapter, we discussed the thermodynamic parameters involved in current collector design for anode-less Li-ion battery. To achieve 2D uniform Li deposition, it is necessary that the current collector possess a low nucleation overpotential. The Li adsorption energy on the current collector surface signifies the thermodynamic nucleation overpotential and the interfacial energy describes the thermodynamic stability of the Li interface during plating. The hBN/Cu Janus current collector proposed in this chapter showed superior properties as compared to graphene/Cu current collector. The hBN/Cu shows low thermodynamic nucleation overpotential while also demonstrates negative interfacial energy that enables the 2D uniform Li deposition. Furthermore, we also could confirm the capability of hBN/Cu current collector to suppress the galvanic corrosion by limiting the charge transfer during Li plating. In Chapter 3, we investigated interfacial phenomena and ion transport related with silver nanocrystals nucleation mechanism. The interfacial energetics that describes thermodynamic stability of the interface could be used to elucidate growth mechanism in uniform Ag nanocubes synthesis. The heterogenous nucleation of Ag nanocubes through AgCl particles was achieved through strong reduction agent (i.e., DMF) that allows Ag+ dissociation from AgCl (100) surface. The stability of AgCl (100) induced the formation of Ag (100) surface, this was indicated by the low interface formation energy, negative interfacial energy, and low strain energy. The presence of PVP surface directing agent further stabilized the Ag (100) to allow Ag (100) surface to the dominant surface, thus formed uniform Ag nanocubes. We also further investigated early nucleation phenomena of Ag nanocrystals by investigating shear rate and solvent environment reduction strength by developing new MD simulation protocol to model Ag+ dynamics and reduction leading to the formation of Ag clusters. We found that the stronger the shear rate and solvent reduction strength the larger the clusters produced. Interestingly, the strong shear rate also induced the formation of flatter and more rounded clusters. In the last chapter (Chapter 4), we presented in-depth studies on ion transport and dynamics in single-ion conduction covalent organic framework (COF) for aqueous Zn-ion battery and in electrolyte additives design for high-performance Li-ion battery. We demonstrated that the high stability of the aqueous Zn-ion battery with COF solid electrolyte was originated from the superior ion conduction behavior of the TpPa-SO3Zn0.5 as compared to the conventional liquid electrolyte (LE). The migration of Zn2+ ions under electric field clearly shows that in the TpPa-SO3Zn0.5 the Zn-ions were transported in relatively uniform distribution in z-direction, while in the LE irregularity was observed. This can be further confirmed through the fraction of Zn-O coordination, in the TpPa-SO3Zn0.5 coordination with O from H2O was far more dominant as compared to that of LE (i.e., mostly coordinated with O (SO4 2-). In the following section, we discussed on how the dynamics of additives (Li-salts) can be used to rationalize the SEI formation. We showed that the interesting behavior of DFBP- and NO3- anion to move towards the anode in the direction of electric field with orderly distribution was important to ensure the dual-layer SEI formation (i.e., LiF and Li3N) could occur at the anode surface. The low LUMO energy level of DFBP- anion further confirmed that once it reached the anode it can act as F-source which enables the formation of LiF layer. The same goes for the NO3- anion since it has the second lowest LUMO energy level. Hence, through the MD simulation on ion transport dynamics and DFT calculation, we could provide theoretical evidence on the dual-layer SEI formation mechanism.