Electrochemical properties of LiFePO_4 thin films prepared by pulsed laser deposition

摘要

Lithium iron phosphate (LiFePO_4) thin film electrodes were prepared by pulsed laser deposition (PLD). The thin films were annealed at various temperatures under argon gas flow and the influence of annealing temperature on their electrochemical performance was studied. The thin films annealed at 773 and 873 K exhibited a couple of redox peaks at 3.4 V (versus Li/Li~+) that are characteristics of the electrochemical lithium insertion/extraction of LiFePO_4. Atomic force microscopy (AFM) observation revealed that the film annealed at 773 K (773K-film) consisted of small grains with 50 nm in thickness, and the grain size increased with an increase of annealing temperature. Because of its small-sized grains, the 773 K-film showed high rate capability and the discharge capacity at 10 mu A maintained 65 percent of that at 25 nA. However, the discharge capacity of the 773 K-film was ca. 10 percent smaller than that of the film annealed at 873 K, indicating that annealing at 773 K is slightly insufficient to obtain well-crystallized LiFePO_4. From these results, it was concluded that a point of optimization between high rate capability and capacity would be found between 773 and 873 K.