High Performance Microbatteries for Integrated Power via Nanoimprinting of 3-D Electrodes

Abstract

The realization of autonomous IOT sensors and devices will require the development of high performance microbatteries. Though numerous microfabrication methods lead to successful creation of sub-millimeter scale electrodes, practical approaches that provide cost-effective nanoscale resolution for energy storage devices remain elusive. We have developed an approach for the direct imprint patterning of crystalline metal oxides using a soft polymer master and inks containing high concentrations of crystalline nanoparticles dispersed in solvent and/or in sol-gel precursors to a desired inorganic phase wherein high aspect ratio nanostructures and sub-100 nm features are easily realized. The technique is further extended to stack the nanostructures by deploying a layer-by-layer imprint strategy. Here we illustrate the utility of this direct patterning technique by the fabrication of high-performance TiO2 nanoelectrode logpile arrays for lithium-ion microbattery anodes and by the fabrication of a fully integrated lithium-ion microbattery made from LiMn2O4Li4Ti5O12 nanoparticles and gel polymer electrolyte. For the TiO2 anode structures, the critical electrode dimension is below 200 nm, which enables the structure to possess favorable rate capability even under discharging current density as high as 5000 mAg-1. By sequential imprinting, electrodes with three-dimensional (3D) woodpile architecture were readily fabricated. The height of architecture can be easily controlled by the number of stacked layers while a constant surface-to-volume ratio is maintained resulting in a proportional increase of areal capacity with the number of stacked layers. The combination leads to efficient use of the material and the resultant specific capacity (250.9 mAhg-1) is amongst the highest reported. The fully integrated 3D microbattery is fabricated by first imprinting a LiMn2O4 cathode grid array followed by coating the grid array with a polymer separator and then backfilling the structure with a Li4Ti5O12 nanoparticles to form the anode. The full cell battery is shown to exhibit an attractive combination of high energy density, superior capacity retention (40% at 300 C) and high-power density (855.5 μWcm-2μm-1), comparable to some of the best microsupercapacitors. The fabrication strategy proposed here can also be applied to other electroactive materials for use in energy storage systems.