Preparation and characterization of high-density spherical Li 0.97Cr 0.01FePO 4/C cathode material for lithium ion batteries

Abstract

LiFePO 4 is the new generation cathode material for lithium ion batteries. To improve the powders’ pile density is considered as the important researching direction. One effective way is to prepare powders composed of spherical particles. Spherical amorphous FePO 4· xH 2O powders were synthesized by controlled crystallization method, using Fe(NO 3) 3, H 3PO 4 and NH 3 as the raw materials. The FePO 4· xH 2O powders were pre-heat treated at 520 °C for 20 h in air to obtain spherical hexagonal FePO 4 powders. The FePO 4 powders were homogeneously mixed with Li 2CO 3, Cr(NO 3) 3 and sucrose with certain molar ratios, and then sintered at 800 °C for 16 h in N 2. The spherical olivine Li 0.97Cr 0.01FePO 4/C powders were finally obtained through carbothermal reduction process. The composition, structure, morphology, and physicochemical properties of FePO 4· xH 2O, FePO 4 and Li 0.97Cr 0.01FePO 4/C powders were characterized in detail by DTA/TGA, ICP, XRD, SEM, XPS, laser particle size analysis, and tap-density testing. It is observed the tap-density of the spherical Li 0.97Cr 0.01FePO 4/C powders is as high as 1.8 g cm −3, which is remarkably higher than the non-spherical LiFePO 4 powders reported. At current of 0.005, 0.05, 0.1, 0.25 and 1.0 C, the composite cathode materials have initial discharge specific capacity of 163, 151, 142, 131 and 110 mAh g −1, respectively. The material also shows excellent cycling performance. The high-density spherical Li 0.97Cr 0.01FePO 4/C cathode material can be used in the lithium ion batteries to greatly increase the batteries’ energy density. To further improve the material's pile density and rate capability is considered as the researching direction.