Enhanced reaction kinetics enabled by a bi-element co-doping strategy for high-performance ternary Si-based anodes of Li-ion batteries

• A novel family of ternary AlSi x P (x=2/3, 2, 6) were synthesized for the first time. • Electronic structures and Li-ionic transportation properties are analyzed. • The AlSi 6 P has the fastest electronic conductivity and Li-ion diffusion. • The AlSi 6 P shows the best Li-storage performances. • The dual-element co-doping strategy is extended to form a universal method. The slow electron and Li-ion transport as well as poor ability to resist against volume variation restrict severely the Si anodes commercialization. Herein, we, for the first time propose a three-in-one approach by co-introducing Al and P into Si to form the complete solid solutions of AlSi x P (x=2/3, 2, 6) by a facile and low-cost mechanical ball milling method. As LIBs anodes, first-principles calculations and experimental measurements demonstrate that the AlSi 6 P sample has the fastest Li-ionic and electronic conductivities among materials of AlSi 2/3 P, AlSi 2 P, AlSi 6 P and Si 8 , thus offering the best Li-storage performances of large reversible capacity, high energy efficiency, long cycling life and fast rate capability. The crystallographic, spectrographic and electrochemical characterizations demonstrate that the AlSi 6 P sample stores Li-ions by a reversible process of Li-intercalation reaction and then conversion reaction where a Li-ionic conductor of LiSi 2 P 3 , and electronic conductors of Li 12 Al 3 Si 4 and Li 15 Si 4 were produced simultaneously, thus delivering excellent Li-storage performances. The AlSi 6 P@graphite composite achieves 1,496 mA h g -1 after 100 cycles at 500 mA g -1 , 1,058 mA h g -1 after 500 cycles, and 1,159 mA h g -1 at 10,000 mA g -1 , thus holding the promise to be applied in the near future. This co-doping strategy provides guidance and a new direction for the design of new energy materials.