ALD-ENABLED CATHODE-CATALYST ARCHITECTURES FOR LI-O2 BATTERIES

Abstract

The Li-O2 electrochemical redox couple is one of the prime candidates for next generation energy storage. Known for its impressive theoretical metric for specific energy, even current practically obtainable values are competitive with state of the art Li-ion intercalation chemistries and the achievable performance of batteries featuring this nascent technology will continue to improve as fundamental scientific challenges in each component of the device are addressed. The positive electrode is particularly complicated by its role as a scaffold for oxygen reduction and evolution, exhibiting sluggish kinetics, poor chemical stability, and limited cyclability due to parasitic side reactions. Fortunately, recent Li-O2 research has shown some success in improving the performance and cyclability of these O2 cathodes by shifting toward nanostructured architectures with catalytic functionalizations. Atomic layer deposition (ALD) is one of the most promising enabling technologies for fabricating these complex heterostructures. Offering precise control of film thickness, morphology, and mass loading with excellent conformality, this vapor-phase deposition technique is applied in this work to deposit thin film and particle morphologies of different catalyst chemistries on mesostructured carbon scaffolds. This thesis dissertation discusses: (1) development of a lab-scale infrastructure for assembly, electrochemical testing, and characterization of Li-O2 battery cathodes including a custom test cell and a state of the art integrated system for fabrication and characterization, (2) design, fabrication, testing, and post-mortem characterization of a unique 3D cathode architecture consisting of vertically aligned carbon nanotubes on an integrated nickel foam current collector, (3) atomic layer deposition of heterogeneous ruthenium-based catalysts on a multi-walled carbon nanotube sponge to produce a freestanding, binder-free, mesoporous Li-O2 cathode with high capacity and long-term cyclability, (4) evaluation of dimethyl sulfoxide as an electrolyte solvent for non-aqueous Li-O2 batteries, and (5) investigation of the relative importance of passivating intrinsic defects in carbon redox scaffolds vs. introduction of heterogeneous OER/ORR catalysts for improving the long-term stability and cyclability of these Li-O2 electrodes.