A methodology for batch-fabricating hundreds of submillimeter thin-film solid-state batteries was used in conjunction with a combinatorial materials synthesis technique. This approach allowed for the simultaneous creation of many solid-state microbatteries that had LiyMnxNi2-xO4 cathodes, where x varied continuously from 0.2 to 1.8 and y varied from 2.7 to 3.7 in the as-deposited films. Sputtered lithium phosphorous oxynitride (LiPON) was used as an electrolyte, while evaporated, micropatterned Li metal served as the anode layer. The composition, thickness, and microstructure of the cathodes were examined using X-ray energy-dispersive spectroscopy, synchrotron-based X-ray diffraction, Rutherford backscattering spectroscopy, stylus profilometry, inductively coupled plasma mass spectroscopy, and scanning electron microscopy. Electrochemical cycling data allowed for cell performance to be correlated to cathode composition and structure. Cathodes with a composition of LiMn1.4Ni0.6O4 had both the highest specific capacity as well as the longest high-potential (4.7 V) discharge plateau, while cells with higher Mn content had a longer 4 V discharge plateau, a result that qualitatively agrees with similar studies on conventional bulk-fabricated cathodes of the same material. (C) 2003 The Electrochemical Society.