Nano- and Microscale Architectures for Energy Storage Systems
The properties of a material as given by the crystal structure can be modified or changed completely by the microstructure architecture. Properties attributed to an insignificant fraction of the material, such as the surface atoms or defect sites, can become material-dominant properties if that fraction of the material is amplified through an appropriate architecture. High surface area forms, in which the material is predominantly surface sites, can have completely different properties than a non-architectured material of the same composition.
In the first part of this work, we discuss coatings to enable microarchitectures for 3D microbatteries. 3D batteries require high surface area structures in order to expand their electrode mass per limited footprint. Increased electrode magnitudes allow a battery to store more energy, and utilizing a high surface area design allows this without increasing ion diffusion distances as would thick monoliths of equivalent electrode mass. A variety of anodes and cathodes have been designed and tested following this principle, and require new electrolyte coatings to be developed to suit them. We design and instrument to deposit these coatings, and demonstrate plasma polymerized PEO-like polymer coatings as versatile solid state electrolyte films that should be compatible with a variety of 3D microbattery architectures. Our electrolyte coatings are analyzed by impedance spectroscopy, and their ionic conductivity is compared amongst various classes of depositions and various Li-ion concentrations.
In the second part of this work, we explore the versatility of nano-architectured materials. High surface area iron oxide aerogels have already been discovered to be useful scaffolds for the paramagnetic iron oxide nanoparticles that form in situ in aerogel synthesis. We have found that the high concentration of surface defects in this material give the aerogels high capacities >100 mAh/g as Li-ion cathodes. Additionally, nanoporous silicon has already been discovered to add stability to and extend the cycle life of silicon as a Li-ion anode. We explore the versatility of this material for the use as anodes in other battery chemistries.