High volumetric energy density of LiFePO4/C microspheres based on xylitol-polyvinyl alcohol complex carbon sources

Abstract

High volumetric energy density LiFePO4/C electrode was synthesized by wet ball-milling, spray drying and carbothermal reduction using xylitol-polyvinyl alcohol (PVA) as complex carbon sources. The fused xylitol with certain viscosity is readily coated on the surface of ferric phosphate (FePO4) during ball milling. PVA hydrogel not only forms a film on the surface of FePO4, which fixes the coating of xylitol to form a gel network, but also acts as a dispersing agent to make the precursor particles disperse more uniformly. The unique properties of the complex carbon sources result in a homogenous carbon-coating all over the primary submicron LiFePO4 particles (100–200 nm in diameter) to form a core-shell structure, and the regular microsphere particles (2–10 μm in diameter) are composed of the primary particles connected by a gel-conductive carbon network. This unique structure provides a Li+ diffusion channel and improves the electronic conductivity. The synthesized LiFePO4/C exhibits high electronic conductivity (2 × 10−1 S cm−1) and high tap density (1.6 g cm−3) with excellent electrochemical performance (at room and low temperatures) and high volumetric energy density (617.8 Wh L−1 at 10 C rate).