Lithium diffusion in sputter-deposited lithium iron phosphate thin-films

Thin films of lithium iron phosphate (LiFePO4, LFP), with a thickness between 80 nm and 320 nm are prepared by ion beam sputter deposition. X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy show that the films exhibit the desired structure, morphology, and chemical composition. Chrono potentiometry and cyclic voltammetry are carried out to determine the electrochemical behavior of the LFP films. Within these electrochemical measurements, a well-defined lithium intercalation/deintercalation reaction at around 3.45 V vs. Li/Li+ and a specific capacity of 104 mAh g−1 are observed. Moreover, a quite high cycling stability is found: Measurement data at 1C rate indicate a capacity fading of only 20% after ≈1700 charge–discharge cycles. In addition, the diffusion of lithium within the LFP thin films is studied by cyclic voltammetry and galvanostatic intermittent transition technique. Within these measurements it is observed that the lithium kinetics in the sputter-deposited thin films is about two orders of magnitude faster, compared to the powder material and thin films deposited by pulsed laser deposition. This behavior may be explained by the strong texture of the sputtered films.

► LFP thin film electrodes are prepared by ion beam sputtering. ► Capacity and cycling stability show that the films are technically applicable. ► The films exhibit a strong texture in (210) and (311) direction. ► The lithium diffusivity of the films is found to agree to theoretical predictions.