(Invited) Nanoporous Materials for Fast and Reversible Electrochemical Energy Storage

Abstract

In this talk, we examine ways that solution processed nanostructured materials can be used to address both fundamental and practical issues relevant to next generation electrochemical energy storage. Materials with appropriate porous architectures can be synthesized using a range of solution phase methods, including polymer templating, nanoparticle assembly, and selective solution phase dealloying of mixed metal solid-state precursors. We begin with nanoporous materials for application in fast charging pseudocapacitors, with a goal of both defining the limits of pseudocapacitance in nanostructured materials and of establishing design rules for synthesizing highly capacitive materials. We find that in optimized nanoporous materials, the nanoscale structure and porosity can produce a very desirable combination of electrical connectivity, electrolyte access to the interior of the material, ample surface redox sites, and very short solid-state diffusion lengths for lithium ions, all of which facilitate fast charge and discharge. Perhaps more importantly, many nanoscale materials appear to show suppression of the intercalation induced phase transition that can cause kinetic limitations in bulk materials. Similar porous architectures can also be used to increase stability and cycle life in high capacity alloy-type anode materials that normal show significant strain related degradation. Using X-ray microscopy, we are able to directly image changes in pore structure upon cycling, so that materials and architectures can be optimized for stable cycling. Taken together, these results emphasize the key role played by nanoscale porosity in electrochemical energy storage materials.