Layered 2D Electrode Architecture for High-Power Lithium Ion Microbatteries

The power density of a lithium ion battery is predominantly limited by poor ionic and electronic pathways in the battery electrodes.  To overcome these limitations, we have fabricated positive electrodes composed of a two-dimensional (2D) layer-by-layer electrode architecture using electrophoretic deposition. In this architecture, alternating layers of multi-walled carbon nanotubes (MWNT) and active lithium metal oxide nanoparticles are electrophoretically assembled onto a current collector. Each active metal oxide nanoparticle is precisely placed to make intimate contact with the conductive MWNT layers, eliminating all other electrode additives such as carbon black and polymeric binder (figure 1). Lithium manganese oxide nanoparticles (LiMn₂O₄, 300nm) are used as a model active material while MWNT are used as the scaffold. These multilayer electrodes demonstrate excellent rate capability up to 10C and cycling stability for over the 100 cycles tested (figure 2) in a Li/liquid electrolyte/LiMn₂O₄ cell. We observe that the electrode capacity per cm²increases linearly with the number of stacked layersat a rate of 0.06 mAh/per layer. Therefore, the capacity per footprint area can be increased by increasing the number of stacked layers. These multilayer electrodes are fabricated at room temperature and atmospheric pressure, and the assembly time per layer is less than 60 seconds.

As the number of layers is increased, the dependence of the electrode morphology on rate performance and cycle life is studied though galvanostatic cycling, cyclic voltammetry, electrochemical impedance spectroscopy and physical characterization techniques such as atomic force microscopy (AFM) and scanning electron microscopy (SEM). Multi-layer electrodes with higher capacity active materials such as the lithium-rich layered  nickel-manganese-cobalt oxide will also be fabricated to further increase the capacity per footprint area of the microbattery [1, 2].

Acknowledgment: Financial support for this work was provided by the Department of Defense.

1. Thackeray, M., Kang, SH.,  Johnson, CS.,  Vaughey, JT., Benedek, R.,  and Hackney, SA., Li₂MnO₃-stabilized LiMO₂ (M = Mn, Ni, Co) electrodes for lithium-ion batteries. Journal of Materials Chemistry, 2007. 17: p. 15.

2. W.C. West, J.S., M.C. Smart, B. V. Ratnakumar, S. Firdosy, V. Ravi, M. S. Anderson, J. Hrbacek, E. S. Lee, and A. Manthiram, Electrochemical Behavior of Layered Solid Solution Li2MnO₃-LiMO₂ (M=Ni, Mn, Co) Li-Ion Cathodes with and without Alumina Coatings. Journal of the Electrochemical Society, 2011. 158: p. 7.