Controlling Nanomaterial Assembly to Improve Material Performance in Energy Storage Electrodes

Abstract

Nanomaterials have enabled significant breakthroughs in energy storage capabilities. In particular, the use of nanoscale components in lithium-sulfur and lithium-oxygen batteries have generated energy densities 2-3x greater than today’s lithium-ion batteries. However, a major roadblock to commercially viable applications of nanomaterials is the ability to cost-effectively manufacture electrode-scale films while still maintaining precise control over the nanoscale morphology. In this regard, electrophoretic deposition (EPD) provides a promising tool for large-scale manufacture of nanomaterial systems using conventional liquid processing techniques. During EPD, the use of electrochemical equilibria to stabilize suspensions of nanomaterials eliminates the need for additives and provides a mechanism to control the placement of individual nanostructures on both 2D and 3D substrates through the application of an electric field. The viability of this process for large scale manufacture is demonstrated by integrating EPD electrode fabrication with nanomaterial synthesis processes on a benchtop roll-to-roll platform. Using this approach, lithium-sulfur and lithium-oxygen electrodes are fabricated that demonstrate enhanced mass-specific performance compared with identical material compositions assembled using conventional techniques. For lithium-oxygen batteries, the role that catalyst assembly plays in dictating the performance of the battery is elucidated and improved through EPD. Likewise, for lithium-sulfur batteries, the coating of an elemental sulfur layer is engineered in conjunction with an all-carbon EPD assembled electrode to produce one of highest capacity and most reversible lithium-sulfur cathodes ever reported. Overall, this thesis demonstrates the role of nanomaterial assembly in determining the energy storage performance of electrode-scale films and presents a method to control this assembly that is amenable to large-scale manufacture.