Solid Interfaces in Lithium Ion Batteries

It is difficult to imagine modern life without batteries: they are present in our mobile phones, laptop computers, automotive vehicles, and even more vital devices, such as pacemakers. Most of these gadgets are powered by lithium (Li) ion batteries, in part due to their high voltage window and relative longevity. While this 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 use of fossil fuels for transportation and energy generation. The replacement of currently used anodes by Li metal is one of the most promising puzzle pieces involved in the solution to this problem. However, a myriad of obstacles hinders its commercialization, many of which are related to phenomena happening at the interface between the anode and the electrolyte.

In this thesis, some of the interfaces present in Li-ion and Li-metal batteries are explored. From a purely mathematical standpoint, interfaces are simply two-dimensional (2D) constructs. However, in real materials, their properties are determined by the atomic structure in their vicinity, thus making them more akin to 2.5D systems. Given the high complexity of such interfacial structures, this thesis is organized in a bottom-up approach. First, we study the possibility of using twisted bilayer graphene, a novel material that, similar to interfaces, can be described as being 2.5D, for electrochemical applications, including Li-ion technologies. Next, some of the interface-related issues that plague Li-ion and Li-metal batteries are scrutinized. Among them, this work focuses on the formation and growth of dendrites, on the ionic conductivity of components of the solid electrolyte interphase (SEI), and on the development of surface voids and pits during the discharge process. Using a well-established electrodeposition model for solid electrolytes, a carefully engineered polymer composite separator is conceptualized to harness advantageous properties of its components at the interfaces between these materials. Battery cells with this composite are tested and revealed to fully prevent dendrite growth. The synergistic interaction between two of the most common SEI components is also probed, and the interface between them is shown to significantly enhance the conduction of charge carriers, thus opening pathways for further engineering of the SEI. By combining first-principles methods with thermodynamic modeling, the importance of considering explicit interfaces in ab-initio calculations is highlighted in the context of void and pit formation. Excellent agreement between our modeling techniques and experimental results was achieved in all-solid-state symmetric cells containing interlayer materials. We also investigate the importance of current collector selection for ensuring high-power outage from anode free batteries at low values of stateof-charge. Finally, the impacts that halogen doping can have on surface energy and particle shape of a promising material for alkaline batteries is inspected, and the effect that dopant choice and concentration can have on unstable decomposition is elucidated.