New Designs and architectures of electrochemical energy storage devices
Ajayan, Pulickel M.
Doctor of Philosophy
Superior performance of Li-ion batteries led an immediate adaptation of these batteries in portable electronics and demands have rapidly increased due adoption in electric vehicles. Development of novel form-factors of portable electronics and need for increasing the driving range of electric cars close to 500 miles per charge requires multifunctional batteries. Future generation batteries are expected to be an integrated part of device (car) structure. Current Li-ion batteries are multilayer device which are compact and volumetrically efficient but are limited to rectangular or cylindrical shapes, which constrains the form factors of devices. The advent of smart devices/objects has further generated interest in self-powered electronics with integrated storage. Such energy conversion-storage hybrids will require batteries that can be integrated directly into the object or surface of choice as well as with energy harvesting devices. This work focuses on the fabrication of unconventional battery designs that can be inconspicuously accommodated into devices and applications without constraining their form factor. The major challenge of seamless integration of these energy storage systems into electronic devices and household objects has been solved. The first part of this work explains the concept and development of novel fabrication process for the Li-ion batteries. We have developed a multi-step spray painting process to fabricate rechargeable Li-ion on a variety of materials such a metal, glass, ceramic and flexible polymer substrates. This fabrication process could have significant impact on the design, implementation and integration of energy storage devices as well as on the electronic device design. We have also explored the idea of spray painting solid Li-ion electrolytes based on lithium lanthanum zirconium oxide (LLZO) to solve the safety issues related to the liquid electrolyte used in spray paintable batteries. Use of solid state electrolyte is also expected to facilitate the fabrication of spray paintable batteries in ambient conditions. LLZO is a fast Li-ion conductor at room temperature and is one of the best choices for solid state electrolytes. We have studied the solution based processing of LLZO to fabricate thin, mechanically strong electrolyte membranes. We have also studied the chemical stability of this materials with common processing materials used in battery industry which led to the room temperature phase transformation in this material. Further, we have developed hybrid architecture of Li-ion battery electrode. A hybrid of Li-ion battery cathode (LiFePO4) and pseudo-capacitor material results in a very interesting characteristic of the electrode which ultimately gives an ultra-fast charge discharge capability to Li-ion batteries. The last part of this work explains the monolithic design for graphite oxide based supercapacitors. Graphite oxide is shown to possess good ionic conductivity in the presence of absorbed water which led to realization of fully functional monolith supercapacitor.