Tin phosphides are attractive anode materials for ultrafast lithium-ion batteries (LIBs) because of their ultrahigh Li-ion diffusion capability and large theoretical-specific capacity. However, difficulties in synthesis and large size enabling electrochemical irreversibility impede their applications. Herein, an in situ catalytic phosphorization strategy is developed to synthesize SnP/CoP hetero-nanocrystals within reduced graphene oxide (rGO)-coated carbon frameworks, in which the SnP relative formation energy is significantly decreased according to density functional theory (DFT) calculations. The optimized hybrids exhibit ultrafast charge/discharge capability (260 mA·h·g−1 at 50 A·g−1) without capacity fading (645 mA·h·g−1 at 2 A·g−1) through 1500 cycles. The lithiation/delithiation mechanism is disclosed, showing that the 4.0 nm sized SnP/CoP nanocrystals possess a very high reversibility and that the previously formed metallic Co of CoP at a relatively high potential accelerates the subsequent reaction kinetics of SnP, hence endowing them with ultrafast charge/discharge capability, which is further verified by the relative dynamic current density distributions according to the finite element analysis.Graphical abstractDownload : Download high-res image (191KB)Download : Download full-size image