Electrode materials composed of micrometer- and sub-micrometer-sized spherical particles are of interest for lithium ion batteries (LIBs) because spheres can be packed with higher efficiency than randomly shaped particles and achieve higher volumetric energy densities. Here we describe the synthesis of lithium iron phosphate (LFP) phases as cathode materials with spherical morphologies. Spherical Li3Fe2(PO4)3 particles and LiFePO4 spheres embedded in a carbon matrix are prepared through phase separation of precursor components in confinement. Precursors containing Li, Fe, and P sources, pre-polymerized phenol-formaldehyde (carbon source), and amphiphilic surfactant (F127) are confined in 3-dimensional (colloidal crystal template) or 2-dimensional (thin film) spaces, and form spherical LFP particles upon heat treatment. Spherical Li 3Fe2(PO4)3 particles are fabricated by calcining LiFePO4/C composites in air at different temperatures. LiFePO4 spheres embedded in a carbon matrix are prepared by spin-coating the LFP/carbon precursor onto quartz substrates and then applying a series of heat treatments. The spherical Li3Fe2(PO 4)3 cathode materials exhibit a capacity of 100 mA h g-1 (83% of theoretical) at 2.5 C rate. LiFePO4 spheres embedded in a carbon matrix have specific capacities of 130, 100, 83, and 50 mA h g-1 at C/2, 2 C, 4 C, and 16 C rates, respectively (PF-600-2), revealing excellent high-rate performance.
Bibliographical noteFunding Information:
This material is based upon work that was supported by the Department of Energy Office of Science under Award Number DE-SC0008662 . Parts of this work were carried out in the University of Minnesota Characterization Facility, which receives partial support from the NSF through the MRSEC, ERC, MRI, and NNIN programs. We thank Professor William H. Smyrl for access to his dry room and electrochemical equipment and Professor R. Lee Penn for use of her powder X-ray diffractometer.
- Carbon nanocomposite
- Colloidal crystal template
- Lithium ion battery
- Lithium iron phosphate