Thin film encapsulation for secondary batteries on wafer level

This paper presents results concerning the realization and characterization of thin film encapsulated waferlevel 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 m, 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)CoO2 and LiXC 6 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 lamina tes. 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 m 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.