title: Designing high-performance electrochemical energy-storage nanoarchitectures to balance rate and capacity.
abstract: The impressive specific capacitance and high-rate performance reported for many nanometric charge-storing films on planar substrates cannot impact a technology space beyond microdevices unless such performance translates into a macroscale form factor. In this report, we explore how the nanoscale-to-macroscale properties of the electrode architecture (pore size/distribution, void volume, thickness) define energy and power performance when scaled to technologically relevant dimensions. Our test bed is a device-ready electrode architecture in which scalable, manufacturable carbon nanofoam papers with tunable pore sizes (5-200 nm) and thickness (100-300 μm) are painted with ~10 nm coatings of manganese oxide (MnOx). The quantity of capacitance and the rate at which it is delivered for four different MnOx-C variants was assessed by fabricating symmetric electrochemical capacitors using a concentrated aqueous electrolyte. Carbon nanofoam papers containing primarily 10-20 nm mesopores support high MnOx loadings (60 wt%) and device-level capacitance (30 F g(-1)), but the small mesoporous network hinders electrolyte transport and the low void volume restricts the quantity of charge-compensating ions within the electrode, making the full capacitance only accessible at slow rates (5 mV s(-1)). Carbon nanofoam papers with macropores (100-200 nm) facilitate high rate operation (50 mV s(-1)), but deliver significantly lower device capacitance (13 F g(-1)) as a result of lower MnOx loadings (41 wt%). Devices comprising MnOx-carbon nanofoams with interconnecting networks of meso- and macropores balance capacitance and rate performance, delivering 33 F g(-1) at 5 mV s(-1) and 23 F g(-1) at 50 mV s(-1). The use of carbon nanofoam papers with size-tunable pore structures and thickness provides the opportunity to engineer the electrode architecture to deliver scalable quantities of capacitance (F cm(-2)) in tens of seconds with a single device.
authors: US Naval Research Laboratory, Surface Chemistry Branch (Code 6170), Washington, DC 20375, USA. megan.sassin@nrl.navy.mil
authors: Megan B
authors: MB
authors: Sassin
authors: Cheyne P
authors: CP
authors: Hoag
authors: Bradley T
authors: BT
authors: Willis
authors: Nathan W
authors: NW
authors: Kucko
authors: Debra R
authors: DR
authors: Rolison
authors: Jeffrey W
authors: JW
authors: Long
mesh_terms: D017076:Computer-Aided Design; D011211:Electric Power Supplies; D004563:Electrochemistry / Q000295:instrumentation; D004735:Energy Transfer; D004867:Equipment Design; D019544:Equipment Failure Analysis; D017895:Manganese Compounds / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010087:Oxides / Q000737:chemistry*; D010316:Particle Size
chemical_list: D017895:Manganese Compounds; D010087:Oxides; C027424:manganese oxide