Accelerating Li-Ion Diffusion in LiFePO4 by Polyanion Lattice Engineering.

Despite the widespread commercialization of LiFePO₄ as cathodes in lithium-ion batteries, the rigid 1D Li-ion diffusion channel along the [010] direction strongly limits its fast charge and discharge performance. Herein, lattice engineering is developed by the planar triangle BO₃ ^3- substitution on tetrahedron PO₄ ^3- to induce flexibility in the Li-ion diffusion channels, which are broadened simultaneously. The planar structure of BO₃ ^3- may further provide additional paths between the channels. With these synergetic contributions, LiFe(PO₄)_0.98(BO₃)_0.02 shows the best performance, which delivers the high-rate capacity (66.8 mAh g^-1 at 50 C) and long cycle stability (ultra-low capacity loss of 0.003% every cycle at 10 C) at 25 °C. Furthermore, excellent rate performance (34.0 mAh g^-1 at 40 C) and capacity retention (no capacity loss after 2500 cycles at 10 C) at -20 °C are realized.