Lithium iron phosphate spheres as cathode materials for high power lithium ion batteries

摘要

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 Li_3Fe_2(PO_4)_3 particles and LiFePC＞4 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_3Fe_2(PO_4)_3 particles are fabricated by calcining LiFePO_4/C composites in air at different temperatures. LiFePO_4 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 Li_3Fe_2(PO_4)_3 cathode materials exhibit a capacity of 100 mA h g~(-1) (83% of theoretical) at 2.5 C rate. LiFePO_4 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.