High Loading Oxide Anodes For Lithium Ion Batteries Via A Superelastic Graphene Composite Approach

ABSTRACT HIGH LOADING OXIDE ANODES FOR LITHIUM ION BATTERIES VIA A SUPERELASTIC GRAPHENE COMPOSITE APPROACH Zhichao Zhang Dr. I-Wei Chen Although nanotechnology has ushered in many new materials storing a high density of electrochemical energy, the performance has only been demonstrated at low material densities, typically ~0.15 g cm-3 and ~ 1 mg cm-2. Such densities fall far short of the loading requirement of commercial electrodes, which is 1.6 g cm-3 and 10 mg cm-2. Yet progress in overcoming this problem has been slow because of fundamental thermodynamic and kinetic difficulties. This thesis solves the problem for anodes of lithium-ion batteries. We start by developing a new graphene network monolith that is superelastic, meso-porous, three-dimensional and metallic conducting. The network already features excellent electrochemical performance, but it can also support relatively insulating active materials while endowing them much improved conductivity to aid electrochemical reactivity. With active-material nanoparticles robustly deposited and adhered to the network, the three-dimensional composite monolith, starting as an composite aerogel, can be non-destructively and conformally deformed to high compression ratios to reach the requisite volumetric and areal loadings and to obtain an anode that fits into a coin cell. Although the resulting high-density electrode already has most of its void space removed, it still has undisturbed nanoparticles, with their local structure connected to a continuous conduit of liquid and ion transport. This allows active electrochemical processes to proceed in the assembled cell at high charging/discharging rates. The active materials studied are SnO2, GeO2, ZnO, Fe2O3 and TiO2. Except for TiO2, they feature theoretical capacities ranging from 2152 mAh g-1 to 988 mAh g-1, but also suffer from volumetric expansions varying from 376% to 93% when Li is incorporated by insertion, conversion and alloying reactions. Such large expansion is usually destructive rendering the materials useless, but when such materials in the form of nanoparticles are incorporated into our composites, they have delivered superior areal and volumetric capacities much higher than those of high-performance experimental materials in the literature and even commercial graphite anode. This thesis has thus demonstrated a promising approach that can help transition nanomaterials to practical use in lithium-ion batteries. Specifically, it provides several new anodes that can realistically replace commercial graphite anode with significantly improved performance