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.

► Li/LFP semi-3D MBs on Si substrates showed high pulse power and stable electrochemical behavior.
► The CuS-coated LFP 3DMB is capable of delivering even higher pulse power and energy density.
► These batteries are designed to have small footprint and yet provide sufficient power and energy to operate MEMS devices.
► We developed an inexpensive and simple EPD method for LFP cathode deposition for 3D microbatteries.