Zhao Zijian, Tian Guiying, Sarapulova Angelina, Melinte Georgian, Gómez-Urbano Juan Luis, Li Chengping, Liu Suya, Welter Edmund, Etter Martin, Dsoke Sonia
CIC energiGUNE , Parque Tecnológico C/Albert Einstein 48 , 01510 Miñano , Alava , Spain.
International Center for New-Structured Materials (ICNSM) , Zhejiang University (ZJU) , Zheda Road 38 , 310027 Hangzhou , P. R. China.
ACS Appl Mater Interfaces. 2019 Aug 21;11(33):29888-29900. doi: 10.1021/acsami.9b08539. Epub 2019 Aug 12.
The carbon coating strategy is intensively used in the modification of conversion-type anode materials to improve their cycling stability and rate capability. Thus, it is necessary to elucidate the modification mechanism induced by carbon coating. For this purpose, bare ZnMnO, carbon-derivative-coated ZnMnO, and carbon-coated ZnO-MnO composite materials have been synthesized and investigated in-depth. Herein, high-temperature synchrotron radiation diffraction is used to monitor the phase transition from ZnMnO to ZnO-MnO composite during the carbonization process. The electrochemical performance has been evaluated by cyclic voltammetry, galvanostatic cycling, and electrochemical impedance spectroscopy. The carbon- and carbon-derivative-coated samples display well-improved cycling stability in terms of suppressed electrode polarization, a moderate increase in resistance, and slight capacity variation. The influence of carbon coating on the intrinsic conversion process is investigated by ex situ X-ray absorption spectroscopy, which reveals the evolution of Zn and Mn oxidation states. This result confirms that the strong capacity variation of the bare ZnMnO is induced not only by the reversible charge storage in the solid electrolyte interphase but also by the phase evolution of active materials. Carbon coating is an effective method to prevent the additional oxidation of MnO to MnO, which leads to a stabilization of the main conversion reaction.
碳包覆策略被广泛应用于转化型负极材料的改性，以提高其循环稳定性和倍率性能。因此，有必要阐明碳包覆引起的改性机理。为此，合成了裸露的ZnMnO、碳衍生物包覆的ZnMnO以及碳包覆的ZnO-MnO复合材料，并进行了深入研究。在此，利用高温同步辐射衍射监测碳化过程中从ZnMnO到ZnO-MnO复合材料的相变。通过循环伏安法、恒电流循环和电化学阻抗谱对电化学性能进行了评估。碳包覆和碳衍生物包覆的样品在抑制电极极化、电阻适度增加和容量轻微变化方面表现出显著改善的循环稳定性。通过非原位X射线吸收光谱研究了碳包覆对本征转化过程的影响，揭示了Zn和Mn氧化态的演变。该结果证实，裸露的ZnMnO的强容量变化不仅是由固体电解质界面中的可逆电荷存储引起的，也是由活性材料的相演变引起的。碳包覆是防止MnO进一步氧化为MnO₂的有效方法，这导致了主要转化反应的稳定。
