水热法是广泛应用于锂离子电池Si@C电极材料的一种制备方法,其反应条件是影响产物最终形貌和性能的重要因素, 采取最佳的反应工艺可以大大提升材料的电化学性能。本研究中, 使用葡萄糖作为碳源, 光伏切割废料硅为硅源, 探究了水热法制备核壳结构Si@C电极材料的最优工艺, 分别研究了温度、 原料浓度、 反应时间和原料比例对产物的形貌、 性能的影响以及相互之间的关系, 并得到最佳反应条件。在该条件下(葡萄糖浓度为0.5 mol·L^-1, 硅与葡萄糖重量比为0.3:1, 反应温度190 ^oC, 反应时间9 h), 得到了包覆完整、 粒径适中的Si@C电极材料(CS190-3), 对以该样品为负极的扣式半电池进行电化学测试, 在655 mA·g^-1的电流密度下, 其首圈放电比容量为3369.5 mAh·g^-1, 经过500次循环剩余容量为1405.0 mAh·g^-1。倍率测试中, 在6550 mA·g^-1的电流密度下,其剩余容量为937.1 mAh·g^-1,当电流密度恢复至655 mA·g^-1时,电池放电比容量仍可恢复至1683.0 mAh·g^-1。

Silicon (Si) has been considered as the potential material for the next-generation lithium-ion batteries (LIBs) for its high capacity (4200 mAh·g^-1, Li₂₂Si₅) and suitable working voltage (about 0.25 V vs. Li/Li⁺). However, the cycling stability and electrochemical performance of Si anode become significant challenges because of low intrinsic conductivity and huge volume variation (about 400%) during cycling processes. In addition, the repeated formation and destruction of surface solid electrolyte interphase (SEI) film will continuously consume the electrolyte and cause damage to LIBs. Carbon (C) materials, such as graphite, carbon spheres and tubes, have been widely applied to ameliorate the conductivity and restrict the volume change of Si anode, which guarantees electrical performance. Especially, a Si@C core-shell structure is preferred to perform a high capacity and relatively good cycle stability. The hydrothermal process has been commonly used to prepare Si@C anodes for LIBs, therefore, it is significant to optimize the preparing conditions to achieve ideal electrochemical performance. In this study, glucose was taken as the carbon source, using the Si waste from the photovoltaic industry as raw materials to prepare Si@C core-shell structure by hydrothermal process. The preparing parameters have been evaluated and optimized, including temperature, reaction time, raw material composition, and mass ratio.

The optimal preparing process was proceeded in the solution with a glucose concentration of 0.5 mol·L^-1 and a Si/glucose mass ratio of 0.3. Then, it was treated in a hydrothermal reactor at 190 ^oC for 9 h. The obtained Si@C anode candidate (Sample CS190-3) was tested with a coin half-cell. The specific capacity after the first cycle reached 3369.5 mAh·g^-1, and the remaining capacity after 500 cycles 1405.0 mAh·g^-1 in a current density of 655 mAh·g^-1. Moreover, for the rate testing, it retained the discharge capacities of 2328.7 mAh·g^-1, 2209.8 mAh·g^-1, 2007.1 mAh·g^-1, 1769.2 mAh·g^-1, 1307.7 mAh·g^-1 and 937.1 mAh·g^-1 at the charge rates of 655 mA·g^-1, 1310 mA·g^-1, 2620 mA·g^-1, 3930 mA·g^-1, 5240 mA·g^-1, and 6550 mA·g^-1, respectively. And it was recovered to 1683.0 mAh·g^-1 when the current density was restored to 655 mA·g^-1. In addition, the EIS data revealed that the half-circle radius of the sample obtained by using the optimal conditions (Sample CS190-3) in the low-frequency region was greatly reduced, and the Warburg impedance became the smallest. This work can provide an important approach, and make a significant impact in the preparation of Si/C anode material for LIBs.