Preparation and characterization of high-density spherical Li0.97Cr0.01FePO4/C cathode material for lithium ion batteries

LiFePO4 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 FePO4·xH2O powders were synthesized by controlled crystallization method, using Fe(NO3)3, H3PO4 and NH3 as the raw materials. The FePO4·xH2O powders were pre-heat treated at 520 °C for 20 h in air to obtain spherical hexagonal FePO4 powders. The FePO4 powders were homogeneously mixed with Li2CO3, Cr(NO3)3 and sucrose with certain molar ratios, and then sintered at 800 °C for 16 h in N2. The spherical olivine Li0.97Cr0.01FePO4/C powders were finally obtained through carbothermal reduction process. The composition, structure, morphology, and physicochemical properties of FePO4·xH2O, FePO4 and Li0.97Cr0.01FePO4/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 Li0.97Cr0.01FePO4/C powders is as high as 1.8 g cm−3, which is remarkably higher than the non-spherical LiFePO4 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 Li0.97Cr0.01FePO4/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.