Thin Film Encapsulation for Secondary Batteries on Wafer Level

This paper presents results concerning the realization and characterization of thin film encapsulated wafer-level batteries. Initially, the technology concept for the construction and hermetic encapsulation of chip-size lithium-ion secondary batteries on wafer level is introduced. Parylene and thin-film metal deposition was used for hermetic encapsulation of the batteries. With this technology, battery sizes between 1 mm² and 1 cm², and as thin as 225 mum, can be fabricated. The chemical compatibility of the EC/DEC electrolyte with the encapsulation material was proven. To characterize the encapsulation layer, optical light microscopy and transmitting light microscopy have been used. Li_(1-x)(Ni)CoO ₂ and Li_xC₆ were used as active intercalation materials for cathode and anode electrode respectively. Using a small fraction of PVdF binder is essential for achieving a high energy density. In this work, the focus was set on increasing the energy density of active battery laminates. To obtain a high discharge capacity, the preparation of battery materials was revised and the lamination process was optimized. Electric measurement on laminated battery foils with an area of 0.96 cm² and a thickness of less than 220 mum has been carried out. As a result a capacity density of 1.33 mAh/cm² was reached while cycling a battery sample under laboratory conditions. The presented technology allows the transformation of the high energy density of cylindrical or prismatic cells to integrated micro batteries