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

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_xP (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 AlSi₆P sample has the fastest Li-ionic and electronic conductivities among materials of AlSi_2/3P, AlSi₂P, AlSi₆P and Si₈, 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 AlSi₆P sample stores Li-ions by a reversible process of Li-intercalation reaction and then conversion reaction where a Li-ionic conductor of LiSi₂P₃, and electronic conductors of Li₁₂Al₃Si₄ and Li₁₅Si₄ were produced simultaneously, thus delivering excellent Li-storage performances. The AlSi₆P@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.