Electrophoretic deposition of lithium iron phosphate cathode for thin-film 3D-microbatteries

An electrophoretic deposition (EPD) method has been developed for the first time to prepare thin-film LiFePO4 cathodes. The effects of polymers and surface-active additives in the electrolytic bath, voltage and deposition protocol have been studied with the aim of obtaining highly adhesive, compact pristine LiFePO4 and polymer-LiFePO4 composite films to be utilized in planar and three-dimensional microbatteries. The samples were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX). XPS and TOFSIMS. These methods confirmed the presence of a polymer binder and its homogeneous lateral distribution in the composite EPD-LiFePO4 cathode. Li/LiFePO4 semi-3D concentric microbatteries (3DCMB) on perforated silicon substrates showed a peak-pulse-power capability of 175 mW cm(-2) and stable electrochemical behavior for over 200 cycles at 100% DOD. Coating the LiFePO4 with a thin layer of copper sulfide improved the cell performance even more. The 3D-LiFePO4-CuS-coated batteries are capable of delivering peak pulse power greater than 200 mW cm(-2) and an energy density of 6-10 mWh cm(-2) - adequate for the needs of microsystems. (C) 2011 Elsevier B.V. All rights reserved.