Properties of nano-crystalline LiMn2O4 thin films deposited by pulsed laser deposition

Properties of LiMn2O4 thin films deposited on polished stainless steel substrates at 400 °C and 200 mTorr of oxygen by pulsed laser deposition have been characterized by electrochemical measurements and physical analyses. The film was mainly composed of nano-crystals less than 100 nm. A maximum specific capacity of 141.9 mAh/g cycled between 3.0 and 4.5 V with a current density of 20 μAh/cm2 has been achieved. The film exhibited an excellent cycling stability up to 500 cycles. The low charge-transfer resistance at high potentials as revealed by AC impedance resulted in high charge/discharge potential and more capacity. The effect of overdischarge was limited and Jahn–Teller effect was overcome to a significant extent in this nano-crystalline film. Ex situ XRD, Raman and XPS provided supporting evidence in the changes in structure, reactivity and cycling stability of nano-crystalline LiMn2O4 film cathodes under different charge/discharge states and cycling tests. SEM images also revealed the stability of the surface topography after a long-term cycling test.