(569a) MEMS-Enabled High-Surface-Area Structures for Fast Charge and Discharge Battery Electrodes

Advancements in MEMS technologies in recent years have given rise to a number of autonomous miniaturized electronic devices, which have lead to the need to fabricate similarly scaled electrochemical energy storage systems. Due to the limited available area on these micro-scale devices, design and fabrication of efficient powering systems with enhanced performance becomes a challenge. A common approach for improving charge and discharge characteristics of electrochemical energy storage systems involves the utilization of high-surface area 3-D electrodes as current carriers to an electrochemically-active material. MEMS-enabled micro-scale multilayer structures obtained by sequential electroplating of structural and sacrificial layers followed by partial and selective removal of the sacrificial layers were shown to enhance the discharge characteristics of primary Zn-air batteries when electrochemically active Zn was deposited on the structural layers. In this study, ordered electrode micro-structures were fabricated via MEMS techniques comprising a series of photoresist (PR) patterning and sequential electroplating processes. High-aspect ratio molds were prepared by PR deposition, followed by alternating Ni and Cu electrodeposition from their respective plating baths. A second PR molding process was carried out to electroplate Ni anchors on the specific regions of the sidewalls of the multilayer structure. These anchors served as supporting columns for the suspended structure by preventing the Ni layers from collapsing on each other after complete and selective removal of sacrificial Cu layers. The final backbone structure provided a large electrode surface area, as well as a highly conductive electrode assembly. In order to reveal the electrode contribution to the charge and discharge behavior of the electrochemical system, nickel oxyhydroxide (NiOOH) was chosen as a secondary battery chemistry to be deposited on the MEMS-enabled electrodes. Charge and discharge tests were conducted at various rates in a three-electrode system. These tests confirmed the enhanced performance of the electrode where the capacity loss observed in the NiOOH cathode is significantly reduced when the discharge rate is increased from 1 C to 100 C.