UC Berkeley

Electrochemical materials play an increasingly important role in our energy landscape, and understanding their behavior at a molecular level is critical for the design of next- generation electrochemical materials that will meet our energy needs. In this dissertation, I will share my work towards the molecular design of three different classes of electrochemical materials: nanocrystals, membranes, and redox mediators.

In the first part of this dissertation, I describe my work with controlling nanocrystal (NC) surface chemistry. NCs are being actively studied due to their unique optical, thermal, electrochemical, and mechanical properties that make them uniquely suited as energy conversion and storage materials. For applications that involve electron transport to or from the NC, the insulating ligands that are commonly used to stabilize the NCs during their synthesis must be removed. I will describe my work studying and developing a new class of ligand stripping reactions that accomplishes this while preserving colloidal stability for the widest group of NC materials to date. The "naked" NC inks produced by my approach are expected to find use in a wide variety of energy conversion and storage applications.

In the second part of this dissertation, I describe my work developing and study- ing size-sieving membranes for next-generation batteries. Many next-generation battery chemistries, including Li–O2, Li–S, and non-aqueous redox-flow batteries store charge with soluble active-species in non-aqueous electrolytes. Each of these chemistries requires the development of new membranes that are capable of blocking active-species crossover while allowing transport of the working-ion. I have established membranes based on polymers of intrinsic microporosity (PIMs) as a class of size-sieving membranes that accomplish this goal. In this dissertation, I outline my work applying these membranes to two different battery chemistries (Li–S and all-organic non-aqueous redox-flow batteries) and explore the impact of membrane reactivity and swelling on its active-species blocking-ability.

In the third and final part of this dissertation, I describe my work with soluble redox-mediators that aid in the electrodeposition of insulating active-materials for next- generation batteries. Many next-generation battery chemistries, including Li–O2 and Li–S, rely on the electrodeposition of insulating active materials to store charge. This electrodeposition process is usually self-limiting, and leads to limits on battery capacity for a given surface area of current collector. In this dissertation, I describe how I circumvent this limit by designing redox-mediators that allow electron transfer and electrodeposition to be spatially decoupled, leading to the electrodeposition of thick deposits (rather than thin coatings) of the insulating active material.