Electrochemical (de)lithiation of silver ferrite and composites: mechanistic insights from ex situ, in situ, and operando X-ray techniques. Issue 33 (14th August 2017)

• Record Type: Journal Article
• Authors: 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.
• Is Part Of: Physical chemistry chemical physics. Volume 19:Issue 33(2017)
• Page Start: 22329
• Page End: 22343
• Publication Date: 2017-08-14
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c7cp04012a
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The (de)lithiation mechanisms of AgFeO2 and Ag0.2 FeO1.6 were investigated. Abstract : The structure of pristine AgFeO2 and phase makeup of Ag0.2 FeO1.6 (a one-pot composite comprised of nanocrystalline stoichiometric AgFeO2 and amorphous γ-Fe2 O3 phases) was investigated using synchrotron X-ray diffraction. A new stacking-fault model was proposed for AgFeO2 powder synthesized using the co-precipitation method. The lithiation/de-lithiation mechanisms of silver ferrite, AgFeO2 and Ag0.2 FeO1.6 were investigated using ex situ, in situ, and operando characterization techniques. An amorphous γ-Fe2 O3 component in the Ag0.2 FeO1.6 sample is quantified. Operando XRD of electrochemically reduced AgFeO2 and Ag0.2 FeO1.6 composites demonstrated differences in the structural evolution of the nanocrystalline AgFeO2 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 0 and partial reduction of Fe 3+ to Fe 2+ occur on reduction to 1.0 V, resulting in a Li1+ y Fe III Fe II y O2 phase. The Li1+ y Fe III Fe II y O2 phase can then reversibly cycle between Fe 3+ and Fe 2+ oxidation states, permitting good capacity retention over 50 cycles. In the Ag0.2 FeO1.6 composite, a substantial amorphous γ-Fe2 O3 component is observed which discharges to rock salt LiFe2 O3 and Fe 0 metal phase in the 3.5–1.0 V voltage range (in parallel with the AgFeO2 mechanism), and reversibly reoxidizes to a nanocrystalline iron oxide phase.