| A chemical reduction coprecipitation method was used to synthesize SnSbCu alloy anode material. Three novel Si/N-C, Si/Cu/N-C and Si/Sn/N-C composite anode materials were prepared respectively, through mechanical alloying(MA) and high temperature solid state reaction. Microstructure, morphology, and electrochemical properties of the negative electrode materials were tested by X-ray diffraction(XRD), scanning electron microscopy(SEM), transmission electron microscopy(TEM), Raman spectroscopy(Raman), differential thermal analyzer(TG-DTA), constant current charge-discharge, cyclic voltammetry and AC impedance(EIS) techniques. The conclusions were as follows:1. Electrochemical properties of of SnSbCu0.3 alloy anode material outperformed that of SnSb alloy anode material via chemical reduction coprecipitation, due to the added inert metallic copper, which effectively eased the reunion of Sn Sb alloy particles. During lithium insertion and extraction of SnSb alloy, copper, used as a buffer group, significantly reduced the volume expansion of the electrode material, improving its cycle stability. In this paper, initial and second capacity of the SnSbCu0.3 alloy anode material was 1169.2and1064mAh/g, its first coulombic efficiency was91%. After 100 cycles, the specific capacity of the alloy can still reach 821.5mAh/g, and itscapacity retention rate was 77.2%, showing excellent electrochemical properties.2. Dopamine was used as a carbon source to prepare Si/N-C composite anode material through high temperature solid state reaction method, and the coated structure was obtained. At a N-doped carbon coating ratio of 1:1.5, the composite anode material exhibits good electrochemical performance. Its first charge and discharge specific capacity was 2204.9 and 1799 mAh/g, respectively, and its first coulombic efficiency was 83.6%. After 100 cycles the capacity was still 1108.7mAh/g, and the capacity retention rate was 60.2%, which exhibits a higher stability than pure Si.3. In order to improve the stability of Si/N-C composite anode material, A material modification that is made in this study. First, inert metal copper was introduced, with which the silicon was mechanical milling, immediately followed by the carbon-coating process.Resulting product had a nitrogen-doped carbon core-shell structure, with a silicon-copper alloy as a core and a nitrogen-doped carbon shell that exhibits better cycle performance. At a current density of 0.08mA/g, after 100 cycles the capacity was still up to 759mAh/g with a capacity retention rate of 88.4%.4. To further improve the electrochemical performance of Si/N-C composite anode material, this paper tried to prepare Si/Sn/N-C composite anode material using active metal Sn instead of copper through the same mechanical alloying method and high-temperature calcination. Sn, participated into the lithium insertion and extraction reactions, which not only increased Si's conductivity, but also improved charge and discharge capacity. Due to Si and Sn's different charge and discharge voltage platform, the two can use each as a buffer substrate, relieving the problem of volume expansion. When the ratio of Si: Sn was 1: 1, the material possessed the best electrochemical properties. Its first charge and discharge capacity were 881.4mAh/g and 1088.4mAh/g, respectively and first coulombic efficiency was 80.9%. After 100 cycles the capacity was 759.8mAh/g, and the capacity retention rate was 86.2%. Aftercoating the firstcoulombefficiency of the materialincreased by 16.6% compared with that of no coating case, and after100 cycles,the capacity retentionrate increased by38.4%. Nitrogen-dopedcarbon-coated Si/Sn/N-Ccomposite anodematerial exhibitsthe highercoulombic efficiencyandcycle stability. |
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