Nov 28, 2012
Li-ion batteries benefit from hierarchical LiFePO4/C
LiFePO4 has many features that make it a promising cathode material for Li-ion batteries. The compound exhibits a long cycle life, high capacity, low cost, acceptable voltage, environmentally friendly characteristics and high thermal stability. However, its use in large electrical equipment such as electric vehicles (EVs) and hybrid electric vehicles (HEVs) is hampered by poor high-rate performance and low tap density. Now, researchers have synthesized hierarchical LiFePO4/C microspheres that overcome these issues. Formed via a simple solvothermal method, the unique nanostructure of LiFePO4/C microspheres promises excellent lithium storage properties and high tap density.
The Gao group from Beihang University, China, carried out the experiments with a 50 mL autoclave. The scientists chose CH3COOLi, H3PO4 and the inexpensive FeSO4 as a source for lithium, iron and PO4. Glycol was used as a solvent. By adjusting the mole ratio of lithium, iron and PO4 to an appropriate value, hierarchical LiFePO4/C microspheres were formed after the hydrothermal reaction and subsequent carbon coating process.
Characterization revealed that the LiFePO4/C microspheres are uniform with a particle size of 8–10 µm and composed of densely compacted nanosheets with a thickness of 20–30 nm. The gaps between the nanosheets are estimated to be 10 50 nm.
The tap density of the LiFePO4/C composite reaches up to 1.5 g cm–3, which the team attributes to the micro-sized spherical morphology and closely packed primary nanosheets.
As cathode material for lithium-ion batteries, the composite exhibits a high capacity: 155 mAh g–1, 144 mAh g–1, 129 mAh g–1, and 104 mAh g–1 at 0.1 C, 1 C, 5 C and 10 C, respectively. The high performance of the electrode is related to the facile electrolyte infiltration and the short lithium ion transport pathways of the LiFePO4/C microspheres.
Full details can be found in the journal Nanotechnology.
About the author
Wei Wei is a PhD candidate in the School of Chemistry and the Environment at Beihang University, Beijing, China, under the supervision of Prof. Guo Lin. His research focuses on the design of lithium ion batteries and the fabrication of high-performance cathode and anode materials for lithium ion batteries.