Developments in MEMS scale printable alkaline and Li-ion technology (invited paper)

Abstract

Two technologies for MEMS scale cell formation are discussed. First, the fabrication of planar alkaline cell batteries compatible with MEMS scale power storage applications is shown. Both mm scale and sub mm scale individual cells and batteries have been constructed. The chosen coplanar electrode geometry allows for easy fabrication of series connected cells enabling higher voltage while simplifying the cell sealing and electrode formation. The Zn/Ag alkaline system is used due to the large operating voltage, inherent charge capacity, long shelf life, and ease of fabrication. Several cells have been constructed using both plated and spun-on silver. The plated cells are shown to be limited in performance due to inadequate surface area and porosity; however, the cells made from spun-on colloidal silver show reasonable charge capacity and power performance with current densities of up to 200 uA/mm2 and charge capacities of up to 18 mA-s/mm2. Three-cell series connected batteries have been fabricated capable of cell potentials up to 4.5V. Second, a new printing method for interdigitated 3-D cells is introduced. A microfluidic printhead capable of dispensing multiple materials at high resolution and aspect ratio is described and used to form features as small as 5 um in width and aspect ratios of greater than 10:1. Various structures enabled by this method are modeled electrochemically, and the energy and power density improvements are reported.