Three dimensional nanostructured designs for lithium ion batteries
Gowda, Sanketh R.
Ajayan, Pulickel M.
Doctor of Philosophy
The reversible electrochemistry and the superior gravimetric and volumetric energy storage capacities of lithium ion batteries (LIBs) have propelled them as the dominant power source for a range of portable electronic devices. Thin film LIBs are a class of LIBs that have been extensively used for powering Microelectromechanical systems devices, Radio-frequency Identification tags, biomedical sensors and several other low power electronic systems. Thin film electrodes and electrolytes are characteristic of short lithium ion diffusion paths and hence show fast charge/discharge rates. But the thin film battery technology has the major drawback of possessing low energy per footprint area. The three dimensional design for thin film LIBs has been proposed to improve electrode mass loading per footprint area thereby improving the energy delivered by the device. Hence there is interest in assembling the entire battery (current collectors, anode, electrolyte, and cathode) in a three dimensional (3D) nanostructured architecture. This thesis deals with the development and assembly of nanostructured three dimensional designs for Li ion battery components. Several template-based techniques have been used to fabricate nanostructured materials which serve as building blocks for the 3D energy storage devices. Firstly we have addressed the challenging task of fabricating conformal nanostructured polymer electrolytes around nanowire electrode material. The polymer coatings helped in controlling the secondary electrolyte interphase formation and hence in the improvement of cycling characteristics of the nanowire electrode material. We have also fabricated 3D current collectors with both ordered and disordered pore structure. Electrodes coated on 3D nanostructured current collectors showed improved rate capability and energy per footprint area. Finally, we have used a bottom up approach to assemble all essential components (anode, electrolyte, and cathode) of an electrochemical energy storage device onto a single nanowire, and have tested a parallel array of such nanowire devices for its electrochemical performance, hence demonstrating the ultimate miniaturization possible for energy storage devices.