High energy density all-solid-state batteries : a challenging concept towards 3D integration

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 favorbale 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.