DOI: 10.1002/adfm.200701245 High Energy Density All-Solid-State Batteries: A Challenging Concept Towards 3D Integration** By Loı :: c Baggetto, Rogier A. H. Niessen, Fred Roozeboom, and Peter H. L. Notten* 1. Introduction Small-sized integrated batteries will supply energy to numerous wireless autonomous devices, such as small medical implants, hearing aids, integrated lighting solutions and many others. Nowadays approximately one half of the volume of medical implants is used for energy storage in the form of batteries. As the size of most of these devices is expected to become of the order of 0.1 cm 3 , it is evident that a high level of integration will be required in the near future. As a consequence, conventional rechargeable battery technologies are not very attractive, as miniaturization becomes highly problematic. In addition, conventional batteries contain liquid electrolytes, which are based on highly volatile and flammable organic solvents. In order to improve the safety and to prevent the risk of electrolyte leakage, of particular importance for in vivo applications, replacing the liquid by a safer and stable solid-state electrolyte is a stringent requirement. Up until now solid-state-based power sources are produced in small quantities and in an exclusive planar geometry. Planar thin-film solid-state Li-ion batteries have been thoroughly investigated by Bates et al . [1–3] Using Physical Vapor Deposition techniques (PVD), such as RF-sputtering and evaporation, current collectors, anode and cathode materials, as well as solid-state electrolytes had been successfully deposited, resulting in solid-state planar batteries. Currently, several companies are manufacturing these batteries. [4–10] However, these devices exhibit several drawbacks. The use of extremely reactive metallic lithium anodes requires an expensive packaging technology. Moreover, pure lithium is highly volatile and melts at about 181 8C, a temperature usually lower than that applied during the re-flow soldering process, widely used in the electronic industry. Furthermore, due to the planar configuration, a relatively low volumetric energy density of about 50 mAh per micron cathode material thickness and per cm 2 footprint area, i.e. 50 mAh mm 1 cm 2 , has been achieved. [4–10] Recently, Long et al. presented an interesting review, des- cribing various existing ideas to come to new architectures and technologies in the field of 3D miniaturized energy storage FULL PAPER [*] Prof. P. H. L. Notten, L. Baggetto Department of Chemical Engineering and Chemistry Eindhoven University of Technology Den Dolech 2, 5600 MB Eindhoven (The Netherlands) E-mail: peter.notten@philips.com Prof. P. H. L. Notten, Dr. R. A. H. Niessen Philips Research Laboratories, High Tech Campus 4 5656 AE Eindhoven (The Netherlands) Prof. F. Roozeboom NXP Semiconductors Research, High Tech Campus 4 5656 AE Eindhoven (The Netherlands) Prof. F. Roozeboom Department of Applied Physics Eindhoven University of Technology Den Dolech 2, 5600 MB Eindhoven (The Netherlands) [**] We gratefully thank Jeroen van Zijl, Jan Verhoeven, Harold Roosen, Tiny den Dekker, Monique Vervest, Hetty de Barse, Monja Kaiser, Thuy Dao, Peer Zalm and Frans Schraven for their technical and analytical support. This work has been financially supported by the Dutch Science Foundation SenterNovem. Rechargeable all-solid-state batteries will play a key role in many autonomous devices. Planar solid-state thin film batteries are rapidly emerging but reveal several drawbacks, such as a relatively low energy density and the use of highly reactive metallic lithium. In order to overcome these limitations a new 3D-integrated all-solid-state battery concept with significantly increased surface area is presented. By depositing the active battery materials into high-aspect ratio structures etched in, for example silicon, 3D-integrated all-solid-state batteries are calculated to reach a much higher energy density. Additionally, by adopting novel high-energy dense Li-intercalation materials the use of metallic Lithium can be avoided. Sputtered Ta, TaN and TiN films have been investigated as potential Li-diffusion barrier materials. TiN combines a very low response towards ionic Lithium and a high electronic conductivity. Additionally, thin film poly-Si anodes have been electrochemically characterized with respect to their thermodynamic and kinetic Li-intercalation properties and cycle life. The Butler-Vollmer relationship was successfully applied, indicating favorable electrochemical charge transfer kinetics and solid-state diffusion. Advantageously, these new Li-intercalation anode materials were found to combine an extremely high energy density with fast rate capability, enabling future 3D-integrated all-solid-state batteries. Adv. Funct. Mater. 2008, 18, 1057–1066 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1057