Etching Preparation of (010)-Defective LiFePO4 Platelets to Visualize the One-Dimensional Migration of Li+ Ions

To visualize the one-dimensional (1D) migration of Li+ ions along the < 010 >-direction, two kinds of (010)-defective LiFePO4 platelets with different hollow interiors are prepared using the polyethylene glycol (PEG)-assisted hydrothermal reaction of LiOH, FeSO4, and H3PO4 at the Molar ratio of 3:1:1. Owing to the acidic and viscous reaction circumstance in the presence of polymeric PEG, the relatively high concentration of PEG induces the formation of (010)-defective LiFePO4 platelets with a small average length and a small hollow interior. As a Li-ion battery cathode, (010)-defective crystallites with a small hollow interior exhibit higher reversible capacity at each charge discharge cycle, smaller concentration polarization and charge transfer resistance, and bigger Coulombic efficiency and Li-ion diffusion coefficient than (010)-defective LiFePO4 platelets with a large hollow interior. Furthermore, (010)-manifested LiFePO4 rnicrorhombohedra and their surface-etched derivatives could be treated as a comparative couple to prove the probable formation mechanism of (010)-defective LiFePO4 platelets and to visualize their sluggish charge transfers along the (MO) direction.