UC San Diego

All-solid-state batteries show its great potential for being the next-generation source of clean energy barely with safety issues. While current research progress suggests the bottleneck of commercialization of all-solid-state batteries is the high resistivity at the electrode/SE interfaces. The aim of this thesis is to demonstrate how computational efforts can help understand and tackle the interface issues. The content comprises the following three projects: the methodology development (Chapter 2), the optimization of bulk materials (Chapter 3), and combined experimental and theoretical investigation into reactive interfaces (Chapter 4 & 5).

In the first project, we aimed to develop and improve the computational workflow in material science research, especially those related to the interfaces. In the first part of this project, the Nudged Elastic Band (NEB) workflow has been developed with high automation and flexibility; and in the second part, an extension to a traditional molecular dynamics workflow specifically for tracking interface reactions has been implemented.

The intrinsic properties of bulk materials are important to the interfacial properties and, thus, the performance of the full-cell battery. In the second project, we illustrated a computational aided design of bulk material, the Mg-doped Na3V2(PO4)3 cathode Na3+xV2-xMgx(PO4)3/C.

The third project includes chapters 4 & 5, which are interfacial investigations on Na-ion and Li-ion, respectively. In chapter 4, we have demonstrated how thermodynamic approximations based on assumptions of fast alkali diffusion and multi-species equilibrium can be used to effectively screen combinations of Na-ion electrodes, solid electrolytes and buffer oxides for electrochemical and chemical compatibility. In addition to the thermodynamic approximation, ab initio molecular dynamics simulations of the NaCoO 2 /Na 3 PS 4 interface model predict that the formation of [SO4]2- -containing compounds and Na3P are kinetically favored over the formation of [PO4]3- -containing compounds, which has been validated through XPS recently. Chapter 5 investigate the source of reactivity between the sulfide solid electrolyte Li6PS5Cl (LPSCl) and the high-voltage cathode LiNi0.85Co0.1Al0.05O2 (NCA). And both experimental and computational results demonstrated improved stability between NCA and LPSCl after incorporation of the LiNbO 3 coating.