Flexible Solid-State Ge – LiCoO2 Battery: from Materials to Device Application

Design and fabrication of reliable materials with high capacity, cycling stability and good adhesion properties for flexible microbatteries remains a challenge. A 2 µm thick flexible solid-state Ge-LiCoO2 battery was fabricated and the structure, composition, thermal, optical, electrical, and electrochemical properties of the materials that determine and influence its electrochemical potential were investigated. RF-sputtered lithium cobalt oxide (LiCoO2) cathode and lithium phosphorus oxynitride (LiPON) electrolyte films were fabricated at 120 W and 100 W of power, respectively. A ~ 300 nm thick Ge anode was deposited by e-beam. The full-battery was fabricated using conventional and low-cost PVD processes. X-ray diffraction (XRD) and Raman spectroscopy confirms the hexagonal R͞3m phase of annealed LiCoO2. Differential scanning calorimetry (DSC) technique was applied to investigate the thermal behaviour of the LiPON film with a moderate electrical resistivity of 10 8 Ωcm and high optical transmission (> 75%) in the UV-Visible range. Bending experiments were also performed to evaluate thin-films adhesion and stability. Scanning electron microscopy (SEM) technique was used to evaluate the morphology of films surface and the layered structure of the full-battery. This detailed experimental study allows us to understand the discharge behavior of the fabricated Li-ion battery.