<p>Paper-based flexible devices represent a new frontier in electronics technology. The research has focused on the fabrication of the lightweight, and flexible paper-based lithium ion batteries. A lithium ion battery relies on the interplay of multiple components. These components themselves, as well as the processes used to create them, need to be adjusted and modified in order to achieve a fully flexible lithium ion battery. These components include the electrode current collector, active material, and electrolyte. By modifying these components to be fully flexible and resistant to damages caused by deformation, a fully flexible battery can be achieved.</p> <p> </p> <p>Herein, the paper-based platform utilized is key to provide flexibility for the battery components. The goal of this work not only focused on the creation of a paper-based flexible battery to be used as an integrable energy storage system for flexible devices, but also on developing methodologies and processes that can advance the emerging area of paper-based electronics, where different functional units must be fabricated within a single paper substrate. The key to make effective paper-based batteries, is to achieve a highly conductive paper structure as the base. In this work, conductive nanomaterials including carbon nanotubes (CNT) and graphene were used to fabricate conductive paper, where wood microfibers were coated with layers of these nanomaterials via layer-by-layer nanoassembly. These fibers were then combined into paper sheets. The resulting paper offers a conductive and porous base for electronic devices that utilized only small quantities of CNT or reduced graphene oxide (rGO) to provide length resistances of 468 Ω/cm and 74.6 Ω/cm, respectively for each fabricated conductive paper. </p> <p> </p> <p>Flexible lithium ion batteries were then made by using CNT paper-based electrodes and a solid polymer gel electrolyte. The electrodes were made by deposition of lithium active materials over the conductive paper and where shown to be flexible, durable, and light weight. With respect to the electrolyte, a new type of gel electrolyte based on PVDF-HFP was fabricated to overcome problems related to the use of liquid electrolytes in flexible batteries. This gel, which provides a high electrolyte uptake (450% by weight), was made by infusing both liquid and ceramic electrolytes inside a polymer gel structure and demonstrated conductivity up to 10^-4 S/cm. The paper-based battery developed with these new materials has a comparable capacity to commercial batteries and represents a flexible and light weight alternative. The use of ultra-high capacity lithium compounds as cathode materials, such as vanadium pentoxide (with theoretical capacities of 440 mAh/g) in conjunction with rGO-paper as a stand-alone electrode (with a reversible capacity 546 mAh/g) were also explored and results will be discussed. </p> <p> </p> <p>This research has led to the development of a novel method of making a fully flexible lithium ion batteries, using paper-based current collectors, leak proof polymer gel electrolytes and ultra-high capacity lithium ion active materials. Thus, flexible high conductive paper-based current collectors, polymer-gel electrolytes, vanadium based ultra-high capacity cathode electrodes, and graphene-based stand-alone paper-based anodes have been developed and tested.</p> <p> </p>

Indiana University-Purdue University Indianapolis (IUPUI) / The prevalent applications of energy storage devices have incited wide-spread efforts on production of thin, flexible, and light-weight lithium-ion batteries. In this work, lithium-ion batteries using novel flexible paper-based current collectors have been developed. The paper-based current collectors were fabricated from carbon nanotube (CNT)-coated wood microfibers (CNT-microfiber paper). This thesis presents the fabrication of the CNT-microfiber paper using wood microfibers, coating electrode materials, design and assemblies of battery, testing methodologies, and experimental results and analyses. Wood microfibers were coated with carbon nanotubes and poly(3,4-ethylenedioxythiophene) (PEDOT) through an electrostatic layer-by-layer nanoassembely process and formed into a sheet, CNT-microfiber paper. The CNT loading of the fabricated paper was measured 10.1 μg/cm2 subsequently considered. Electrode material solutions were spray-coated on the CNT-microfiber paper to produce electrodes for the half and full-cell devices. The CNT current collector consists of a network structure of cellulose microfibers at the micro-scale, with micro-pores filled with the applied conductive electrode materials reducing the overall internal resistance for the cell. A bending test revealed that the paper-based electrodes, compared to metal ones, incurred fewer damages after 20 bends at an angle of 300o. The surface fractures on the paper-based electrodes were shallow and contained than metallic-based electrodes. The micro-pores in CNT-microfiber paper structure provides better adherence to the active material layer to the substrate and inhibits detachment while bending. Half-cells and full-cells using lithium cobalt oxide (LCO), lithium titanium oxide (LTO), and lithium magnesium oxide (LMO) were fabricated and tested. Coin cell assembly and liquid electrolyte was used. The capacities of half-cells were measured 150 mAh/g with LCO, 158 mAh/g with LTO, and 130 mAh/g with LMO. The capacity of the LTO/LCO full-cell also was measured 126 mAh/g at C/5 rate. The columbic efficiency of the LTO/LCO full-cell was measured 84% for the first charging cycle that increased to 96% after second cycle. The self-discharge test of the full-cell after charging to 2.7 V at C/5 current rate is showed a stable 2 V after 90 hours. The capacities of the developed batteries at lower currents are comparable to the metallic electrode-based devices, however, the capacities were observed to drop at higher currents. This makes the developed paper-based batteries more suitable for low current applications, such as, RFID tags, flexible electronics, bioassays, and displays. The capacities of the batteries at higher current can be improved by enhancing the conductivity of the fibers, which is identified as the future work. Furthermore, fabrication of an all solid state battery using solid electrolyte is also identified as the future work of this project.