Zou Yihui, Zhang Wei, Chen Ning, Chen Shuai, Xu Wenjia, Cai Rongsheng, Brown Christopher L, Yang Dongjiang, Yao Xiangdong
State Key Laboratory of Bio-fibers and Eco-textiles, Collaborative Innovation Center of Marine Biobased Fibers and Ecological Textiles , Institute of Marine Bio-based Materials, Qingdao University , Qingdao 266071 , P.R. China.
Canadian Light Source , Saskatoon S7N 0X4 , Canada.
ACS Nano. 2019 Feb 26;13(2):2062-2071. doi: 10.1021/acsnano.8b08608. Epub 2019 Jan 15.
The polar surface of (001) wurtzite-structured MnO possesses substantial electrostatic instabilities that facilitate a wurtzite to graphene-like sheet transformation during the lithiation/delithiation process when used in battery technologies. This transformation results in cycle instability and loss of cell efficiency. In this work, we synthesized MnO hexagonal sheets (HSs) possessing abundant oxygen vacancy defects (MnO-Vo HSs) by pyrolyzing and reducing MnCO HSs under an atmosphere of Ar/H. The oxygen vacancies (Vos) were generated in the reduction process and have been characterized using a range of techniques: X-ray absorption fine structure, electron-spin resonance, X-ray absorption near edge structure, Artemis modeling, and R space Feff modeling. The data arising from these analyses inform us that the introduction of one Vo defect within each O atom layer can reduce the charge density by 3.2 × 10 C, balancing the internal nonzero dipole moment and rendering the wurtzite structure more stable, so inhibiting the change to a graphene-like structure. Density function theory calculations demonstrate that the incorporation of Vos sites significantly improves the charge accumulation around Li atoms and increases Li adsorption energies (-2.720 eV). When used as an anode material for lithium ion batteries, the MnO-Vo HSs exhibit high specific capacity (1228.3 mAh g at 0.1 A g) and excellent cell cycling stabilities (∼88.1% capacity retention after 1000 continuous charge/discharge cycles at 1.0 A g).
纤锌矿结构的MnO(001)极面具有显著的静电不稳定性，这使得其在用于电池技术时，在锂化/脱锂过程中容易发生从纤锌矿结构向类石墨烯片层的转变。这种转变会导致循环不稳定性和电池效率损失。在本工作中，我们通过在Ar/H气氛下热解和还原MnCO HSs合成了具有大量氧空位缺陷的MnO六角片（MnO-Vo HSs）。氧空位（Vos）在还原过程中产生，并使用一系列技术进行了表征：X射线吸收精细结构、电子自旋共振、X射线吸收近边结构、Artemis建模和R空间Feff建模。这些分析得到的数据告诉我们，在每个O原子层中引入一个Vo缺陷可使电荷密度降低3.2×10 C，平衡内部非零偶极矩并使纤锌矿结构更稳定，从而抑制向类石墨烯结构转变。密度泛函理论计算表明，Vos位点的引入显著改善了Li原子周围的电荷积累并增加了Li吸附能（-2.720 eV）。当用作锂离子电池的负极材料时，MnO-Vo HSs表现出高比容量（在0.1 A g下为1228.3 mAh g）和优异的电池循环稳定性（在1.0 A g下连续1000次充/放电循环后容量保持率约为88.1%）。
