Direct Imprinting of Microelectrodes for HighPerformance Miniature Power Sources
Wenhao Li, 1 Vince Einck, 1 Cheng Li, 1 Yiliang Zhou, 1 Troels Christiansen, 2 Bo B.
Iversen2 and James J. Watkins1
Department of Polymer Science and Engineering, University of Massachusetts1Amherst, MA USA 01003
Department of Chemistry, Aarhus University2
Langelandsgade 140, Aarhus, DenmarkE-mail: watkins@polysci.umass.edu

Microbatteries with form factors comparable to MEMS e.g., microsensors and actuators, offer
exciting opportunities to achieve self-powered, all-on-one-chip devices. Despite significant
advances of the 3D microbattery theories, scalable fabrication of microelectrodes withcomplicated 3D architectures and the assembly of miniature components into a well-functioning
battery remain elusive. Here we utilize soft imprint lithography and functional nanoparticle inks,
including LiMn2O4 (LMO), Li4Ti5O12 (LTO) and TiO2, to fabricate high aspect ratio
microelectrodes. The nanoparticles, either commercial or home-synthesized, bear sub-20 nm
diameters, rendering fine and stable dispersions for imprinting and offering significant
advantages for easy mass and ionic diffusion in the electrochemical processes.1-3 The low
viscosity of imprinting inks facilitates the capillary-driven mold filling. By modulating theelastomer stamp dimensions, we create LMO microelectrodes with aspect ratios of 0.7, 1.7 and3.8 (Figure 1a to 1c). To further improve the aspect ratio, we apply multilayer imprinting
strategy to create woodpile-like 3D TiO2 microelectrodes, achieving user-defined aspect ratios(Figure 1d-1e). The imprinted woodpile electrodes demonstrate specific capacity of 250.9 mAhg1and stable cycling in a lithium-ion battery. Post-cycling SEM imaging (Figure 1f) shows thatthe imprinted feature maintain good structural integrity.
Aside from imprinted electrodes, polymer electrolytes that enable solution deposition onelectrodes are developed to facilitate microbattery full cell fabrication. The resultant
microbattery based on LMO/LTO electrochemical pair demonstrates superior fast chargedischarge capabilities (40% capacity retention at 300 C) and high volumetric power density of
855 μWcm-2μm-1 (Figure 2), which is attributed to the small critical dimension and high surfaceto-volume ratio of the imprinted features. In the last part, we will briefly mention about our workof using initiated chemical vapor deposition to optimize the polymer electrolyte coating quality;4much better uniformity and conformality can be achieved.
Reference:[1]. Li, W.; Christiansen, T. L.; Li, C.; Zhou, Y.; Fei, H.; Mamakhel, A.; Iversen, B. B.; Watkins,J. J., High-power lithium-ion microbatteries from imprinted 3D electrodes of sub-10 nm
LiMn2O4/Li4Ti5O12 nanocrystals and a copolymer gel electrolyte. Nano Energy 2018, 52, 431440.
[2]. Li, W.; Zhou, Y.; Howell, I. R.; Gai, Y.; Naik, A. R.; Li, S.; Carter, K. R.; Watkins, J. J.,
Direct Imprinting of Scalable, High-Performance Woodpile Electrodes for Three-Dimensional
Lithium-Ion Nanobatteries. ACS Appl. Mater. Interfaces 2018, 10 (6), 5447-5454.

[3]. Kothari, R.; Beaulieu, M. R.; Hendricks, N. R.; Li, S. K.; Watkins, J. J., Direct Patterning ofRobust One-Dimensional, Two-Dimensional, and Three-Dimensional Crystalline Metal OxideNanostructures Using Imprint Lithography and Nanoparticle Dispersion Inks. Chemistry ofMaterials 2017, 29 (9), 3908-3918.
[4]. Li, W.; Bradley, L. C.; Watkins, J. J., Copolymer Solid-State Electrolytes for 3D
Microbatteries via Initiated Chemical Vapor Deposition. ACS Appl. Mater. Interfaces 2019, 11(6), 5668-5674.

Figure 1. (a)-(c) imprinted LMO electrodes with aspect ratios of 0.9, 1.7 and 3.8. (d) and (e) top-down
and cross-sectional views of TiO2 woodpile electrodes. (f) post-cycling imaging of TiO2 woodpileelectrode.

Figure 2. (a) discharging profiles of LMO/LTO microbatteries at different C rates. (b) Normalized
capacity of micorbattery as a function of C rates and cycle numbers.