关键词: 水热反应, 核壳结构Si@C材料, 葡萄糖, 锂离子电池负极材料

Abstract:

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.

Key words: hydrothermal reaction, Si@C ball structure, glucose, anode materials