Energy Storage Materials
Utilizing surface area for energy storage enhancements in the microscale
One of our battery projects aims to re-engineer micropower sources that will be integrated with microelectromechanical systems (MEMS). The successful outcome of this area of research addresses a rapidly emerging need, that of developing autonomous MEMS devices. In order to operate independently, these devices must have on-board power from power sources on millimeter (or smaller) scales that deliver milliwatt levels of power for tens of hours. Our approach to this problem is to redesign the battery electrode interface to introduce more surface area per areal footprint. This design provides a strategy for overcoming the classic battery compromise between energy density and power density which plagues 2D configurations.
In addition, we are utilizing increased surface area to allow for the practical use of silicon as a lithium ion battery anode. Silicon has a ultra-high theoretical capacity of 4200mAh/g, more than 10 times that of graphite, but its high capacitiy is also its downfall. The intercolation of such a high volume of lithium causes the silicon lattice to increase to 40 times its original size, leading to rapid device fracture and subsequent failure. We are using a high surface area, mesoporous silicon anode as a way to accomodate the volume expansion, and thin silicon walls to allow for a flexible, rather than a brittle, material.
Finally, we are applying the same mesoporous architectures toward supercapcitors. In this area, we can create nano-particle/templated film hybrids which combine the power and energy-density advantages, respectively, of each material. We can also see intercolation capacity contributions to energy storage in materials usually thought of as incapable of such contributions, due to the increased surface area-to-volume ratios of our materials.