Preparation And Properties Of The Transition Metal-Sn Alloy

Tin（Sn） is considered as an alternative anode material with great promise because of its high theoretical specific capacity of 993 m Ahg^-1 derived from the formation of a Li22Sn5 phase. Nevertheless, the practical application of the tin anode material is seriously hampered by its gigantic volume change（up to 360%） and dramatic mechanical stress generated upon lithiation-delithiation process, thereby leading to rapid capacity fading. To overcome above-mentioned problems, a very effective method is to introduce the inert matrix（denoted as M） and to fabricate the M-Sn alloy. Herein, the inert matrix M is mainly the transition metal, such as Cu, Ni and Co, etc. Because it is lithium-inactive, the M cannot react with lithium upon lithiation-delithiation process. Furthermore, because of the buffering effect of inert M matrix, the M-Sn alloy with decreased volume changes exhibits enhanced electrochemical cycling performances.In this paper, the topic is to enhance the electrochemical cycle performances of the Sn-based anode materials for LIBs, especially using the doped method of introducing the transition metal, such as Cu, Ni and Co, etc. By combining the simple preparation methods like high-energy ball-milling techniques and solvothermal method, three types of transition metal（M= Cu, Co and Ni） dopted M-Sn alloys are parpared. Their structure, component and morphology are then characterized by means of the XRD, SEM and TEM equipments. In addition, with the help of the battery performance tester and electrochemical workstation, their electrochemical performances are also studied. The obtained related research results are as follows:（1） A series of non-stoichiometric Cu-Sn alloys are systematically fabricated by employing the high-energy ball-milling technique. The obtained results show that the non-stoichiometric Cu-Sn alloys are all two-phase. Furthermore, the phase composition is different as the different content of doped Cu. When used as the anode materials for LIBs, the sample with the best specific discharge capacity and cycling life contains Sn content of 70 at.%, which delivers a specific discharge capacity of 457 mAhg^-1 after 20 cycles. By comparing the electrochemical performances in different content of doped Cu, The recipe with the best specific discharge capacity and cycling life is given, which is a significant basis for enhancing the cell performances of the Cu-Sn-based anode materials for LIBs.（2） The zero-dimensional Ni-Sn alloy and the Ni₃Sn₂@reduced graphene oxide（Ni₃Sn₂@rGO） composite are fabricated by a one-step solvothermal method. In the one-step solvothermal process, the particle sizes of Ni-Sn alloy can be controlled by changing the concentration of the raw materials. In addition, the Ni₃Sn₂ alloys in the Ni₃Sn₂@rGO composite with regular quasi-spherical morphology and an average size of 216 nm are homogeneously encapsulated into rGO sheets. And the rGO content is 11.1 wt. % in this composite. The results of cell performances demonstrate that the cycling life of Ni₃Sn₂@rGO composite can be remarkably improved by using promising r GO matrix. The as-prepared Ni₃Sn₂@rGO composite exhibits a reversible capacity of 554 mAhg^-1 after 200 cycles at a current density of 100 mAg^-1. Moreover, a substantial discharge capacity of 422 mAhg^-1 can be also maintained at a current density of 800 mAg^-1.（3） The three-dimensional polygonal Co-Sn alloy is successful prepared by a one-pot solvothermal route. The obtained Co₃Sn₂ nanostructure with reduced gain size of 100-200 nm exhibits anisotropic hexagonal Ni2In-type structure and three-dimensional polygonal morphology. In comparison with the Co sample, anisotropic structure and morphology endow the Co₃Sn₂ nanostructure with enhanced saturation magnetization of 134.01 emug^-1 and coercivity of 131.5 Oe. Furthermore, when used as an anode material for LIBs, the Co₃Sn₂ nanostructure exhibits a reversible capacity of 240 mAhg^-1 after 200 cycles at a current density of 100 m Ag^-1 and a discharge capacity of 168 m Ahg^-1 at a current densityof 1600 m Ag^-1.