Three-dimensional batteries using a liquid cathode
Three-dimensional (3D) battery architectures have emerged as a new direction for powering microelectromechanical systems and other miniature autonomous devices. Although to date there are few examples of fully functioning 3D batteries, these power sources have the potential to achieve high power density and high energy density in a small footprint. Current batteries are composed of solid state systems. In our system, the cathode and electrolyte are combined to form a liquid cathode (or catholyte). This catholyte is based on the lithium-sulfur system, which has a high theoretical gravimetric capacity of 1672 mAh/g.
This dissertation focuses on creating a rechargeable 3D lithium battery using a liquid cathode. The first part of the dissertation describes the liquid cathode, which is a lithium polysulfide. The second part of the covers the formation of the 3D lithium-containing anode and its integration into the battery. Two new routes to achieve 3D lithium anodes have been developed. One approach involves the electrodeposition of lithium onto a 3D nickel current-collector array. The second method involves the electrodeposition of lithium directly onto the current collector through a polymer mold. 3D batteries fabricated using Li2S6 liquid cathodes exhibit power densities of 1.1 mW/cm2 at current densities as high as 0.5 mA/cm2.
Also included in this dissertation is a unique lithium polysulfide gel cathode which has been synthesized using sol-gel processing. Using a non-hydrolytic sol-gel route, a polysulfide-gel cathode has been integrated into a 2D battery. Similar to the liquid cathode, the polysulfide-gel battery requires no separator, i.e., is does not short with the lithium anode. The combination of high surface area (519 m2/g) and pore diameter (2.0 nm) of the silica matrix allows lithium polysulfide to diffuse to and from the current collectors. Cyclic voltammetry shows the electrochemical activity within the same potential window as that of the liquid cathode. First generation polysulfide-gel batteries exhibit areal capacities of 1 mAh/cm2 at a current density of 10 μA/cm2.