关键词: 冶金法, Cu₃Si, 电化学特性, 赝电容, 二级相变

Lithium-ion batteries with high energy density have urgent demand, especially in the fields of pure electric vehicles, smart phones, laptops, wind power generation and energy storage. Therefore, more and more attention has been paid on materials with high energy density, rapid charge/discharge capability and long cycle life. In this paper, pure Cu₃Si phase was prepared by metallurgical process, and the electrochemical characteristics of the as prepared Cu₃Si samples were studied by using CR2025 button half-cell structure with metal lithium sheet as reference electrode and Celgard 2500 as diaphragm. The results showed that, at a current density of 0.1C (420 mA•g^–1), it possessed a first-cycle discharge specific capacity of 759 mAh•g^–1 with a coulomb efficiency of 96.56%. It remained 822 mAh•g^–1 after 200 cycles with a capacity retention rate of 98%. It retained 776, 700, 580, 500, 440 and 405 mAh•g^–1 at a testing rate of 0.1C, 0.2C, 0.4C, 0.6C, 0.8C and 1C, respectively. The specific capacity was stabilized at around 790 mAh•g^–1 when the current density was restored to 0.1C, which did not decrease significantly compared with the initial value. Moreover, the impedance was about 60 Ω, lower than that of the reported Si@C anode. Thus, it suggested that introducing Cu would greatly reduce the charge transfer resistance. It was worth noting that the charge/discharge curve was slope like and had pseudo capacitance characteristics. Furthermore, the cyclic voltammetry (CV) measurement was carried out at scanning rates of 0.1, 0.2, 0.4, 0.6, 0.8 and 1.0 mV/s, respectively. The results discovered for the first time that the as-prepared Cu₃Si possessed the characteristic of both battery and capacitance. They together stored the charges, and the capacitance dominated the contribution. Moreover, an clear step could be observed at 550—600 ℃ in the differential scanning calorimetry (DSC) curve of the as-prepared Cu₃Si sample after discharged, relating to a change in the specific heat capacity. Moreover, the sample phase did not change before and after the charge/discharge process. Therefore, it was determined that the Li⁺ insertion/desertion process of Cu₃Si was not a first-order phase transition but a second-order phase transition process. To be concluded, for Cu₃Si anode materials, the redox process was a second-order phase transition, which exhibited a pseudo capacitive behavior in its electrochemical properties.

Key words: metallurgical method, Cu₃Si, electrochemical characteristics, pseudo-capacitance, second order phase transition