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 TiO ₂ nanoelectrode logpile arrays for lithium-ion microbattery anodes and by the fabrication of a fully integrated lithium-ion microbattery made from LiMn ₂ O ₄ Li ₄ Ti ₅ O ₁₂ nanoparticles and gel polymer electrolyte. For the TiO ₂ 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 LiMn ₂ O ₄ cathode grid array followed by coating the grid array with a polymer separator and then backfilling the structure with a Li ₄ Ti ₅ O ₁₂ 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 ^-2 μm ^-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.