Characterization of crystallized LiMn2O4 thin films grown by pulsed laser deposition

Abstract

LiMn2O4 thin films were grown on stainless steel substrates at 625C and 100 mTorr of oxygen by pulsed laser deposition. The deposited film was highly crystallized with an average crystal size of about 260 nm. The initial discharge capacity of the film was about 53.8 Ah cm-2 m-1 and the capacity decayed at an average rate of about 0.29% per cycle when the film was cycled between 3.0 and 4.5 V vs. Li/Li+, with a current density of 20 A cm-2. It was observed that the grains became smaller and the boundaries of grains became obscure after 100 cycles, indicating that manganese dissolution via loss of MnO may be the main factor leading to the capacity fade in pure thin film LiMn2O4 electrodes. The apparent diffusion coefficient of Li ions, obtained from cyclic voltammetry scans, was of the order of 10-12 cm2 s-1. High charge-transfer resistance was observed at high potentials. Ex-situ X-ray diffraction (XRD) and Raman spectroscopy were used to investigate the structure changes of LiMn2O4 thin film with intercalation/de-intercalation of lithium. XRD results revealed a relatively small lattice change with the removal of lithium in crystallized thin film, compared to that of powder LiMn2O4 cathode.