Nano-structured 3D Electrodes for Li-ion Micro-batteries

Abstract: A new challenging application for Li-ion battery has arisen from the rapid development of micro-electronics. Powering Micro-ElectroMechanical Systems (MEMS) such as autonomous smart-dust nodes using conventional Li-ion batteries is not possible. It is not only new batteries based on new materials but there is also a need of modifying the actual battery design. In this context, the conception of 3D nano-architectured Li-ion batteries is explored. There are several micro-battery concepts that are studied; however in this thesis, the focus is concentrated on one particular architecture that can be described as the successive deposition of battery components (active material, electrolyte, active material) on free-standing arrays of nano-sized columns of a current collector.After a brief introduction about Li-ion batteries and 3D micro-batteries, the electrodeposition of Al through an alumina template using an ionic liquid electrolyte to form free-standing columns of Al current collector is described. The crucial deposition parameters influencing the nucleation and growth of the Al nano-rods are discussed.The deposition of active electrode material on the nano-structured current collector columns is described for 2 distinct active materials deposited using different techniques.Deposition of TiO2 using Atomic Layer Deposition (ALD) as active material on top of the nano-structured Al is also presented. The obtained deposits present high uniformity and high covering of the specific surface of the current collector. When cycled versus lithium and compared to planar electrodes, an increase of the capacity was proven to be directly proportional to the specific area gained from shifting from a 2D to a 3D construction.Cu2Sb 3D electrodes were prepared by the electrodeposition of Sb onto a nano-structured Cu current collector followed by an annealing step forcing the alloying between the current collector and Sb. The volume expansion observed during Sb alloying with Li is buffered by the Cu matrix and thus the electrode stability is greatly enhanced (from only 20 cycles to more than 120 cycles).Finally, the deposition of a hybrid polymer electrolyte onto the developed 3D electrodes is presented. Even though the deposition is not conformal and that issues of capacity fading need to be addressed, preliminary results attest that it is possible to cycle the obtained 3D electrode-electrolyte versus lithium without the appearance of short-circuits.