Characterization of crystallized LiMn₂O₄ thin films grown by pulsed laser deposition

Abstract

LiMn₂O₄ thin films were grown on stainless steel substrates at 625°C 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 µAh cm⁻² µm⁻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 µA 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.

Acknowledgements

This work has been supported by the National University of Singapore under research grants R265-000-133-112 and R265-000-162–112.