Portable society urgently calls for integrated energy supplies. This holds for autonomous devices but even more so for future medical implants. Evidently, rechargeable integrated all‐solid‐state batteries will play a key role in these fields, enabling miniaturization, preventing electrode degradation upon cycling and electrolyte leakage. Planar solid‐state thin film batteries are rapidly emerging but reveal several potential drawbacks, such as a relatively low energy density and the use of highly reactive lithium. Thin film Si‐intercalation electrodes covered with a solid‐state electrolyte are found to combine a high storage capacity of 3500 mAh g–1 with high cycle life, enabling to integrate batteries in Si. Based on the excellent intercalation chemistry of Si, a new 3D‐integrated all‐solid‐state battery concept is proposed. High aspect ratio cavities and features, etched in silicon, will yield large surface area batteries with anticipated energy density of about 5 mWh μm–1 cm–2, i.e. more than 3 orders of magnitude higher than that of integrated capacitors.

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.

A mathematical model for all-solid-state Li-ion batteries is presented. The model includes the charge transfer kinetics at the electrode/electrolyte interface, diffusion of lithium in the intercalation electrode, and diffusion and migration of ions in the electrolyte. The model has been applied to the experimental data taken from a 10μAh planar thin-film all-solid-state Li-ion battery, produced by radio frequency magnetron sputtering. This battery consists of a 320nm thick polycrystalline LiConormalO2 cathode and a metallic Li anode separated by 1.5μm normalLi3PnormalO4 solid-state electrolyte. Such thin-film batteries are nowadays often employed as power sources for various types of autonomous devices, including wireless sensor nodes and medical implants. Mathematical modeling is an important tool to describe the performance of these batteries in these applications. The model predictions agree well with the galvanostatically measured voltage profiles. The simulations show that the transport limitations in the solid-state electrolyte are considerable and amounts to at least half of the total overpotential. This contribution becomes even larger when the current density reaches 0.5mAcm−2 or higher. It is concluded from the simulations that significant concentration gradients develop in both the positive electrode and the solid-state electrolyte during a high current (dis)charge.