MSn5 (M=Fe, Co, Fe0.5Co0.5) are a series of metastable tin-based alloys discovered by Han’s group. Because of the high Sn content and high conductivity of alloying metals (Fe and Co et. al), the MSn5 phases exhibit superior electrochemical properties in lithium ion batteries. For example, 30-50 nm FeSn5 nanospheres can deliver a high capacity of 750 mA h g-1 at 50 mA g-1, and CoSn5 nanospheres exhibit good cycle stability up to 100 cycles. Although these three transition metals Fe, Co, and Ni show similar physical and chemical properties, we fail to synthesize NiSn5 phase by using the same polyol wet chemical method. In this work, we firstly synthesized the new NiSn5 intermetallic phase by adopting an induction synthesis method using Fe3+ and/or Co2+ as induction agent. Furthermore, the crystal structure was resolved using the charge-flipping method, and the growth and electrochemical mechanism were investigated using TEM and ex situ synchrotron XRD.The resutl shows the NiSn5 phase belongs to tetragonal phase in P4/mcc space group, and has stoichiometric Ni atom defects, the actual chemical formula is Ni0.62Sn5. Growth mechanism study reveals that the FeSn5/CoSn5 seed crystal formed after addition of trace of Fe3+/Co2+ plays a vital role in the formation of NiSn5 phase. The existence of FeSn5/CoSn5 seed crystal can effectively reduced the nucleation barrier of NiSn5, and the NiSn5 nanospheres final form through Kirkendall diffusion. The phase evolution investigation reveals that the NiSn5 phase is irreversible after initial discharging/charging processes, unlike the reversible transformation of MSn5 (M=Fe, Co, Fe0.5Co0.5). This result accounts for the failure of NiSn5 synthesis using traditional polyol wet chemical method and the relatively low cyclability of NiSn5. We believe this method can be expanded to synthesize other new alloys which are difficult to produce using the traditional methods. Figure 1 (a) The reaction mechanism of induced synthesis of NiSn5 phase. (b) Synchrotron XRD pattern and Rietveld refinement of NiSn5 phase. (c,d) TEM images of Sn and NiSn5 nanospheres. Acknowledgments This work is supported by the National Natural Science Foundation of China (Grant No. 51901206). Figure 1