Durham Jessica L, Brady Alexander B, Cama Christina A, Bock David C, Pelliccione Christopher J, Zhang Qing, Ge Mingyuan, Li Yue Ru, Zhang Yiman, Yan Hanfei, Huang Xiaojing, Chu Yong, Takeuchi Esther S, Takeuchi Kenneth J, Marschilok Amy C
Department of Chemistry, Stony Brook University, Stony Brook, NY 11794, USA.
Phys Chem Chem Phys. 2017 Aug 23;19(33):22329-22343. doi: 10.1039/c7cp04012a.
The structure of pristine AgFeO and phase makeup of AgFeO (a one-pot composite comprised of nanocrystalline stoichiometric AgFeO and amorphous γ-FeO phases) was investigated using synchrotron X-ray diffraction. A new stacking-fault model was proposed for AgFeO powder synthesized using the co-precipitation method. The lithiation/de-lithiation mechanisms of silver ferrite, AgFeO and AgFeO were investigated using ex situ, in situ, and operando characterization techniques. An amorphous γ-FeO component in the AgFeO sample is quantified. Operando XRD of electrochemically reduced AgFeO and AgFeO composites demonstrated differences in the structural evolution of the nanocrystalline AgFeO component. As complimentary techniques to XRD, ex situ X-ray Absorption Spectroscopy (XAS) provided insight into the short-range structure of the (de)lithiated nanocrystalline electrodes, and a novel in situ high energy X-ray fluorescence nanoprobe (HXN) mapping measurement was applied to spatially resolve the progression of discharge. Based on the results, a redox mechanism is proposed where the full reduction of Ag to Ag and partial reduction of Fe to Fe occur on reduction to 1.0 V, resulting in a LiFeFeO phase. The LiFeFeO phase can then reversibly cycle between Fe and Fe oxidation states, permitting good capacity retention over 50 cycles. In the AgFeO composite, a substantial amorphous γ-FeO component is observed which discharges to rock salt LiFeO and Fe metal phase in the 3.5-1.0 V voltage range (in parallel with the AgFeO mechanism), and reversibly reoxidizes to a nanocrystalline iron oxide phase.
利用同步辐射X射线衍射研究了原始AgFeO的结构以及AgFeO（一种由纳米晶化学计量比的AgFeO和非晶态γ-FeO相组成的一锅法复合材料）的相组成。针对采用共沉淀法合成的AgFeO粉末提出了一种新的堆垛层错模型。使用非原位、原位和操作中表征技术研究了铁酸银AgFeO和AgFeO的锂化/脱锂机制。对AgFeO样品中的非晶态γ-FeO成分进行了定量。电化学还原的AgFeO和AgFeO复合材料的操作中XRD表明，纳米晶AgFeO成分的结构演变存在差异。作为XRD的补充技术，非原位X射线吸收光谱（XAS）深入了解了（脱）锂化纳米晶电极的短程结构，并应用了一种新型的原位高能X射线荧光纳米探针（HXN）映射测量来空间分辨放电过程。基于这些结果，提出了一种氧化还原机制，即在还原至1.0 V时，Ag完全还原为Ag，Fe部分还原为Fe，从而形成LiFeFeO相。然后，LiFeFeO相可以在Fe和Fe氧化态之间可逆循环，在50个循环中保持良好的容量保持率。在AgFeO复合材料中，观察到大量的非晶态γ-FeO成分，其在3.5 - 1.0 V电压范围内放电至岩盐LiFeO和Fe金属相（与AgFeO机制并行），并可逆地再氧化为纳米晶氧化铁相。
