While lithium (Li) ion battery technology has had major successes, at the current rate of progress, it is unlikely to meet the mid-century global demands related to full de-carbonization and interruption of fossil fuel usage for transportation and energy generation. The replacement of currently used anodes by Li metal is one of the most promising alternatives to solve this problem. However, various obstacles hinder its commercialization, many of which are related to phenomena happening at the interface between the anode and the electrolyte. In this talk, some of the interface-related issues that plague Li-ion and Li-metal batteries are discussed. Using a well-established electrodeposition model for solid electrolytes, we conceptualize and engineer a polymer composite separator capable of harnessing advantageous properties of its components at their interfaces. The synergistic interaction between two of the most common components of the solid electrolyte interphase is also probed, and the interface between them is shown to significantly enhance the conduction of charge carriers. By combining first-principles methods with thermodynamic modeling, we explore the importance of interfaces in the context of void and pit formation. A similar methodology is also employed to examine Li intercalation in twisted bilayer graphene systems. The methods and principles used in these studies rely on computational approaches that are broadly applicable — and indeed critical — for applications that require engineering at the nanoscale.