To overcome a major limitation of volumetric energy density, we prepared micrometer-sized LiFePO4 particles with a unique spongelike morphology and a high packing density. Each LiFePO4 secondary particle (6 mu m) consisted of nanoscale (200-300 nm) primary LiFePO4 particles coated with carbon and had nanoscale (100-200 nm) pores throughout. Compared with the nano-LiFePO4 positive electrode material, this carbon-impregnated, spongelike, nanoporous material resulted in a similarly high rate capability plus a 2.5 times greater volumetric energy density.