Preparation Of LiFePO₄/C Materials With Special Morphologies And Their Electrochemical Performance

Lithium ion batteries are considered to be the most promising candidate for electricvehicles because of their high power densities compared to conventional rechargeablebatteries. In this paper, the preparation of LiFePO4/C materials with specialmorphologies and their electrochemical properties have been investigated.Fe5(PO4)4(OH)3·2H2O microflowers were synthesized by a hydrothermalreaction with self-prepared β-FeOOH nanorods as raw materials. The influenceof the reaction time on their structures was studied. And the microflowersmorphology was retained when they were lithiated to prepare LiFePO4/Ccomposites through a carbothermal reduction method. As cathode materials forlithium ion batteries, the as-obtained LiFePO4/C microflowers deliver dischargecapacities of156,70and56mAh g-1at0.1,10and15C, respectively. And thedischarge capacity has almost no degradation after100cycles, compared to theinitial discharge capacity at1C rate.In addition, LiFePO4microplates were synthesized by a solvothermal approach inethanol solvent with self-prepared amorphous FePO4particles as precursors. Themicroplates expose large scale of (010) faces and are composed of nanosheets with asize of50nm and thickness of10nm. When solvent ethanol was replaced by a mixtureof water-ethanol (1/1, by volume) in the reaction, a distinctive morphology: LiFePO4microflower was obtained. After coating carbon, the LiFePO4/C microplates deliverdischarge capacities of157,100and81mAh g1at0.1,10and20C, which are muchbetter than those for LiFePO4/C microflowers.At last, the cathode materials of the spent lithium ion batteries after1500cycles were recovered, and mixed with carbon black and polyvinylidene fluoride(PVDF) binder (the mass ratio was80:15:5) to obtain the regenerated cathodes.The half cells employed lithium foil as a counter electrode. The intercalation ofLi from the lithium foil anode into the LixFePO4/C (0<x<1) cathode wasconducted through charging and discharging to realize the regeneration of spentmaterials. The results indicate that the regenerated LiFePO4/C vs. lithium metalelectrode can deliver the discharge capacities of150,141,131,111,79and50mAh g-1at0.1,0.5,1,5,10and15C, respectively. The comparison of theregenerated LiFePO4/C cathode and unregenerated LixFePO4/C cathode was carried out based on full batteries with graphite electrode as anode. Theregenerated cathode delivers an initial discharge capacity of133mAh g-1at0.1C, which is greater than114mAh g-1of the unregenerated cathode.