Novel Lithium Iron Pyrophosphate (LiFe_1.5P₂O₇) as a Positive Electrode for Li-Ion Batteries

Lithium iron pyrophosphate (LiFe 1.5 P 2 O 7 ) has been synthesized by a wet-chemical method for application in lithium-ion batteries. Structural analysis using X-ray diffraction and high-resolution electron microscopy indicate that LiFe 1.5 P 2 O 7 synthesized at 500 °C, using metal acetates, is crystallized in the monoclinic structure with lattice parameters a = 0.698 76 nm, b = 0.812 36 nm, c = 0.964 22 nm, and β=111.83° ( P 2 1 / c space group). Electrochemical characterization of LiFe 1.5 P 2 O 7 in lithium cells indicates a capacity of 95 mA·h/g obtained in the voltage range 2.5−4.2 V. The resulting incremental capacity indicates a stable structure for the first cycle with the redox peaks at 3.33 and 3.22 V versus Li 0 /Li + . The capacity of LiFe 1.5 P 2 O 7 decreased with cycling number at the rate of 0.22% per cycle while the capacity falls off rapidly in the case of material prepared at higher temperatures.