CuO纳米线储锂电化学行为与机理的原位透射电镜研究

In Situ Transmission Electron Microscopy Observation of the Electrochemical Behavior and Mechanism of CuO Nanowires

过渡金属氧化物是具有前景的锂离子电池负极材料，但是其在电化学反应中的反应行为和反应机制尚不明确。利用原位透射电镜研究了CuO纳米线的首次充放电电化学反应过程。结果表明：放电过程中电化学反应界面沿着CuO纳米线轴向方向移动，且反应的界面始终保持锥形，表明Li^＋离子的传输是从外向内进行的；且锂化的进行引起了纳米线的径向膨胀和轴向延长及弯曲，径向膨胀～40％，轴向膨胀～43．1％，体积膨胀～185．8％。待首次放电完成后，CuO纳米线转化为Cu纳米晶（2～3nm），分散在Li20基体中，而在去锂化后并没有氧化为CuO，而是生成了Cu2O，此不可逆的相转变是造成电池充放电循环中首次不可逆比容量损失的主要原因。

Transition metal oxides have been used as one of the most promising candidates as anode materials for lithium ion batteries （LIBs）. However, their electrochemical process remains unclear. Here we directly observe the dynamic behaviors and conversion mechanism of CuO nanowire in LIBs by in situ transmission electron microscope. The results show that a reac- tion front propagates progressively along the nanowire and always keeps a conical shape during the whole process. The conical reaction interface also verifies that lithiation proceeds from the nanowire surface towards its center. After lithiation, the origi- nally straight CuO nanowire becomes heavily distorted and prolonged. The lithiation process causes an axial elongation of 43. 1%, a radial expansion of 40%, and the total volume expansion of 185%. Also, single crystalline CuO nanowires are found to transform to multicrystaUine nanowires consisting of many Cu nanograins （2 ~ 3 nm） embedded in Li2O matrix. The delithiated product is not CuO but Cu2O, accounting for the irreversible electrochemical process and the large capacity fading of the anode material in the first cycle.