Electrochemical performance of LiFePO4 thin films with different morphology and crystallinity

Abstract

LiFePO4 thin films have been prepared by pulsed laser deposition method on titanium substrates. The influence of the deposition parameters, e.g. substrate temperature, ambient argon pressure, and post-annealing on the crystallinity and morphology of as-deposited thin films are investigated. Well-crystallized pure olivine-phase is obtained under optimized deposition condition (20-30 Pa, 500 degrees C). It shows a high electrochemical activity (83% theoretical capacity) at low current density (0.33 mu A cm(-2), 1/20 C) and elevated testing temperature (45 degrees C). Moderate post-annealing treatment can enhance the utilization of the films further. The deposition of the film at a too high temperature or post-annealing for too long time could introduce Fe impurities, i.e., Li3Fe2(PO4)(3) and Fe-4(P2O7)(3), which can be easily detected by extending the electrochemical test voltage down to 2.5 V. (C) 2009 Elsevier Ltd. All rights reserved.