Novel porous-silicon structures for 3D-interlaced microbatteries

The key challenge in fabricating three-dimensional (3D) microbatteries is the achievement of high-aspect-ratio electrodes to ensure dramatic improvement in the surface-to-volume ratio and charge/discharge rates without a corresponding increase in overall volume. In this work, we present the design of a novel 3D-interlaced microbattery (3D-IMB) for high-energy-density applications. 3D-interlaced structures have been fabricated on a silicon substrate provided with arrays of interlaced micro-containers of anode and cathode materials separated by a porous-silicon wall. Etching of the interlaced structure was performed by photolithography and dry reactive ion-etch process. The nanoporous separator (membrane) between the micro-containers was formed by a metal-assisted anisotropic wet-etching process. Different etching solutions, containing hydrogen peroxide, hydrofluoric acid and ethanol, were tested in order to obtain the proper pore-size in the inter-container partitions. Cycling tests of Li/MoO_xS_y thin-film planar microbatteries with interlaced porous-silicon structures showed stable electrochemical behavior.