Radio frequency magnetron-sputtered LiCoPO4 cathodes for 4.8 V thin-film batteries

Thin-film batteries employing sputtered LiCoPO4 cathode layers, Li3.3PO3.8N0.22 (LiPON) electrolyte, and Li anode films have been successfully fabricated and tested. The cells exhibit a high-voltage charge/ discharge plateau of 4.8 V, with a lower plateau at 2.5 V corresponding to a much higher conductivity phase. Cells fabricated with as-deposited cathode layers are highly resistive and cannot be charged or discharged to appreciable capacities, even at very low rates of approximately C/100. Upon annealing, the films sputtered from the LiCoPO4 target become discontinuous and take on a granular morphology. X-ray diffraction results show that these grains consist of untextured crystalline LiCoPO4 on a Pt current collector layer, a finding further supported by the results from subsequent electrochemical analyses. Thin-film batteries fabricated with crystalline LiCoPO4 cathodes are among the highest voltage thin-film batteries yet reported. (C) 2003 The Electrochemical Society.