Nanostructured metal phosphides are very attractive materials in energy storage and conversion,but their applications are severely limited by complicated preparation steps,harsh conditions and large excess of highly toxic phosphorus source.Here we develop a highly efficient one-step method to synthesize SrvP3 nanostructure based on simultaneous reduction of SnCl4 and PCl3 on mechanically activated Na surface and in situ phosphorization.The low-toxic PCl3 displays a very high phosphorizing efficiency(100％).Furthermore,this simple method is powerful to control phosphide size.Ultrafine Sn4P3 nanocrystals(<5 nm)supported on carbon sheets(Sn4P3/C)are obtained,which is due to the unique bottom-up surface-limited reaction.As the anode material for sodium/lithium ion batteries(SIBs/LIBs),the Sn4P3/C shows profound sodiation/lithiation extents,good phase-conversion reversibility,excellent rate performance and long cycling stability,retaining high capacities of 420 mAh/g for SIBs and 760 mAh/g for LIBs even after 400 cycles at 1.0 A/g.Combining simple and efficient preparation,low-toxic and high-efficiency phosphorus source and good control of nanosize,this method is very promising for low-cost and scalable preparation of high-performance Sn4P3 anode.