Advanced batteries [electronic resource] : material development and device fabrication

Rechargeable batteries are vital in solving imminent energy and environmental issues. Advanced batteries with superior performance and new functionality are desired for applications including novel electronics, electric vehicles, and smart grids. In this thesis, our work on designing novel materials, structures and devices for advanced batteries are presented. In the first part, progresses on high energy lithium sulfur (Li-S) batteries are presented and discussed. The Li-S battery has a specific energy three to five times that of state-of-the-art Li-ion batteries. However, the battery has a poor cycle life due to limitations in the sulfur cathode. To improve the performance of Li-S battery, several nanostructured sulfur cathode have been proposed and realized, including hollow carbon nanofiber-encapsulated sulfur and conductive polymer-wrapped mesoporous carbon/sulfur composite. Discharge capacity of 900 mAh/g and cycle retention of 85% per 100 cycles have been achieved. Moreover, the reaction mechanism of Li-S battery is studied by in-situ X-ray diffraction and imaging. It has been found that results based on in-situ techniques are quite different from previous ex-situ results and common opinions. These results illustrate the importance of in-situ studies and can help guide future designs of Li-S batteries. In the second part, our results on Li2S are presented. Li2S can avoid the safety issue of metallic lithium anode in Li-S batteries. Furthermore, Li2S has capacity one order of magnitude higher than current oxide/phosphate cathodes of Li-ion batteries, and thus leads to rechargeable batteries with specific energy four to six times that of commercial Li-ion batteries. However, Li2S is both electronic and ionically insulating. By using either nanostructures or charging to high potential in the initial cycle, we demonstrate two approaches to activate Li2S to be electrochemically active. Discharge capacity over 800 mAh/g has been achieved and capacity retention as high as 75% per 100 cycles are demonstrated with a discharge capacity of ~550 mAh/g. In the last part, our work on transparent Li-ion batteries is presented as a progress at the device level. Transparent devices are one of the future trends for electronics. As a critical component in electronics, the battery is not transparent yet as both electrode materials and metallic substrate are opaque. We fabricate a grid-like electrode by microfluidics-assisted method to solve this issue. As lines in the grid are smaller than eye's resolution and the gap among lines is filled with transparent PDMS, the whole electrode appears transparent. Batteries with transparency of 60% and energy density of 10 Wh/L have been demonstrated. The energy density could reach 100 Wh/L by optimization. Moreover, the grid-structured electrodes in the transparent battery are stackable without sacrificing the transparency. Future work includes scaling up and further optimization of full cell operations for commercial products.

Keywords: Materials Science and Engineering
Advisor: Cui Yi
Melosh Nicholas A. advisor. Thesis advisor
Prinz F. B. advisor. Thesis advisor