摘要/Abstract
高能量密度的锂离子电池的应用日趋广泛, 寻找兼具高能量密度、快速充放电、长循环寿命能力的材料成为了研究热点. 采用冶金法制备了纯度较高的Cu3Si相, 扣式半电池测试表明, Cu3Si负极在0.1C倍率下首圈放电比容量759 mAh•g–1, 首圈库伦效率96.56%, 循环200圈之后放电比容量是822 mAh•g–1, 容量保持率达到98%. 且其充放电曲线为斜坡状, 具有赝电容特性. 首次发现了Cu3Si材料兼具电池和电容属性, 二者共同储存了电荷, 且以电容贡献率为主. 经嵌锂后的Cu3Si样品的差示扫描量热法(DSC)曲线在550~600 ℃有一个明显台阶, 对应于比热容的变化, 且充放电前后样品的物相并未发生改变, 说明Cu3Si脱嵌锂非一级相变, 而是二级相变. 因此, 就Cu3Si材料而言, 二级相变的氧化还原过程在电化学特性上表现为赝电容行为.
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
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