Recent advances in rechargeable Zn/MnO2 alkaline batteries have shown promise for scalable energy storage systems which provide a safe, low-cost alternative with a demonstrated lifetime over thousands of cycles. This cathode technology is based on a 2-electron Mn redox process where a layered birnessite-type phase has been shown to form after the first cycle with excellent reversibility between the discharge product, Mn(OH)2. Herein, we investigate the reversible reaction between birnessite and Mn(OH)2 with and without a Bi2O3 additive using multimodal structural characterization techniques during active battery cycling. Diffraction results provide evidence of Bi3+ residing in the interlayer of birnessite which prevents irreversible Mn3O4 formation by limiting Mn3+ diffusion within the crystal lattice. Also, upon charge no MnOOH intermediate phases are observed. Instead, X-ray absorption and Raman spectroscopy indicate a disordered, non-crystalline birnessite-type phase consisting of mostly neutral H2O within the interlayer. Birnessite phases will reform without Bi2O3 present, but Mn3O4 formation severely polarizes the potential they are formed at, leading to capacity fade. Also, we discuss the reversible Bi2O3 conversion to Bi0 and its contribution to the observed capacity. We expect the results will provide crucial insight into the development of aqueous, rechargeable battery systems utilizing MnO2.
Low-cost batteries based on Earth-abundant materials are needed for large-scale electrical storage for the grid. Cathodes based almost entirely on Mn oxides would reduce overall battery cost but cycling of...
Rechargeable multivalent-ion batteries are of significant interest due to the high specific capacities and earth abundance of their metal anodes, though few cathode materials permit multivalent ions to electrochemically intercalate within them. The crystalline chevrel phases are among the few cathode materials known to reversibly intercalate multivalent cations. However, to date, no multivalent-ion intercalation electrodes can match their reversibility and stability, in part due to the lack of design rules that guide how ion intercalation and electron charge transfer are coupled up from the atomic scale. Here, we elucidate the electronic charge storage mechanism that occurs in chevrel phase (Mo 6 Se 8 , Mo 6 S 8 ) electrodes upon the electrochemical intercalation of multivalent cations (Al 3+ , Zn 2+ ), using solid-state nuclear magnetic resonance spectroscopy, synchrotron X-ray absorption near edge structure measurements, operando synchrotron diffraction, and density functional theory calculations. Upon cation intercalation, electrons are transferred selectively to the anionic chalcogen framework, while the transition metal octahedra are redox inactive. This reversible electrochemical anionic redox, which occurs without breaking or forming chemical bonds, is a fundamentally different charge storage mechanism than that occurring in most transition metal-containing intercalation electrodes using anionic redox to enhance energy density. The results suggest material design principles aimed at realizing new intercalation electrodes that enable the facile electrochemical intercalation of multivalent cations.
Rechargeable Zn-MnO2 alkaline batteries have been identified as a viable option for the modernization of grid scale energy storage due to their projected cost (<$100/kWh), scalability, and safer components when compared to non-aqueous alternatives.1 For this system to reach its maximum capability, the full Mn4+/2+ redox couple must be reversible over thousands of cycles with high mass loading. This was successfully demonstrated with the incorporation of various electrode constituents which alter the fundamental discharge and charge process of MnO2 to Mn(OH)2.1 Using non-destructive, synchrotron diffraction techniques, we detail the effect of Bi on the breakdown and reformation of birnessite (𝛿-MnO2) during cycling. Further spectroscopic evidence including Raman and X-ray absorption spectroscopy during cycling also provides crucial insights into amorphous phases and variations in redox activity, with and without additives. Early demonstrations of Bi3+ containing constituents with MnO2 in alkaline batteries increased the cyclability of these systems up to hundreds of cycles with low mass loading.2,3 Later investigations followed up by hypothesizing the presence of Bi3+ could potentially catalyze the reduction of Mn3+ to Mn2+ and that upon subsequent charge promotes the formation of a layered, birnessite, MnO2 structure.4 The quick reduction of Mn3+/2+ is critical because the presence of Mn3+ is associated with the irreversible phase change to the Mn3O4 spinel structure.5 Figure 1 shows the birnessite (001) reflection at ~7.1 Å rapidly shift to lower d-spacings upon discharge until ~6.9 Å then directly convert to Mn(OH)2 where the corresponding ~4.8 Å reflection appears. Notably, no crystalline intermediates such as MnOOH or Mn3O4 form during cycling. Also, upon charge the birnessite (001) reflection does not appear until the third potential plateau even though the Mn(OH)2 (001) reflection fades linearly until the end of charge. Due to these observations, further spectroscopic techniques were used to probe these reactions. Using operando Raman spectroscopy we observed a limited formation of an amorphous Mn3O4 during discharge and a disordered birnessite phase formation occurring on the second plateau of charge in the presence of Bi3+. These investigations provide new insight into the intermediates and formation mechanisms of Mn-based alkaline battery electrodes in the presence of Bi2O3. The presence of both Cu and Bi additives are necessary to stabilize the reversible processes occurring during electrochemical cycling. However, the synergistic relationship between Cu and Bi is not extensively investigated. Previous synchrotron XANES and XRF mapping showed that the Cu2+/0 redox couple was occurring during the Mn3+/2+ reduction. It was hypothesized that the Cu acts as a redox mediator and rapidly forms the Mn2+ species during discharge.6 Here we use a X-ray absorption spectroscopy quick scanning to monitor the Mn, Bi, and Cu redox activity which are all relating to the possible mediation of Mn reduction and oxidation. Using multiple techniques, we provide a complete understanding of the role of both bismuth and copper containing constituents on the redox transitions of MnO2 in alkaline electrolyte. Wholistic investigations combining multiple operando techniques are critical to the development of rechargeable alkaline batteries by advancing the fundamental design of these systems. Figure 1 (a) Operando X-ray diffraction data between 3-7.5 Å of the first cycle of Bi2O3-modified birnessite electrode in KOH electrolyte. (b) Corresponding galvanostatic discharge and charge at a rate of C/3. (c) Lattice parameter ‘c’, the interlayer spacing, of the birnessite phase during the first cycle. (d) The relative peak intensities of the birnessite and Mn(OH)2 (001) reflection during the first cycle. References: 1. Yadav, G. G.; Gallaway, J. W.; Turney, D. E.; Nyce, M.; Huang, J.; Wei, X.; Banerjee, S., Nature Communications 2017, 8, 14424. 2. Dzieciuch, M. A.; Gupta, N.; Wroblowa, H. S., Journal of The Electrochemical Society 1988, 135 (10), 2415-2418. 3. Wroblowa, H. S.; Gupta, N., Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1987, 238 (1), 93-102. 4. Im, D.; Manthiram, A., Journal of The Electrochemical Society 2003, 150 (1), A68-A73. 5. Gallaway, J. W.; Hertzberg, B. J.; Zhong, Z.; Croft, M.; Turney, D. E.; Yadav, G. G.; Steingart, D. A.; Erdonmez, C. K.; Banerjee, S., Power Sources 2016, 321, 135-142. 6. Gallaway, J. W.; Yadav, G. G.; Turney, D. E.; Nyce, M.; Huang, J.; Chen-Wiegart, Y.-c. K.; Williams, G.; Thieme, J.; Okasinski, J. S.; Wei, X.; Banerjee, S., Journal of The Electrochemical Society 2018, 165 (13), A2935-A2947. Figure 1
Recent advances in rechargeable Zn/MnO2 alkaline batteries have shown promise for scalable energy storage systems which provide a safe, low-cost alternative to current Li-ion technologies and have a demonstrated lifetime over thousands of cycles. This cathode technology is based on a 2-electron Mn redox process where a layered birnessite-type phase has been shown to form after the first cycle with excellent reversibility between the discharge product, Mn(OH)2 when Bi2O3 and Cu constituents were added to the electrode.1 For this system to reach costs < $100/kWh, the complete reduction to Mn2+ must be reversible with high mass loading (> 20 mAh/cm2). To get a complete understanding of the role of Bi2O3 in the reversible formation of a birnessite phase a multimodal structural characterization strategy is necessary to identify all the various intermediates formed during battery cycling. Spectroscopic evidence including Raman and X-ray absorption spectroscopy during cycling provide crucial insights into intermediate phases and variations in redox activity, with and without additives. Early demonstrations of Bi3+ containing constituents with MnO2 in alkaline batteries increased the cyclability of these systems up to hundreds of cycles with low mass loading.2,3 Later investigations followed up by hypothesizing the presence of Bi3+ could potentially catalyze the reduction of Mn3+ to Mn2+ and that upon subsequent charge promotes the formation of a layered, birnessite, MnO2 structure.4 The quick reduction of Mn3+/2+ is critical because the presence of Mn3+ is associated with the irreversible phase change to the Mn3O4 spinel structure.5,6 Figure 1 shows the birnessite vibrations at 510, 578 and 635 cm-1 form only at the top of charge with the Mn3O4 spinel vibration at 659 cm-1 present throughout the entire charging process. However, with the addition of the Bi2O3 a birnessite phase forms earlier in the charge process allowing for the facile conversion between the Mn(OH)2 and charged birnessite phase. This birnessite phase could not be identified through diffraction methods and is therefore considered a highly disordered phase that exists as a short-lived intermediate during battery operation. Using operando diffraction and X-ray near edge absorption spectroscopy (XANES) we characterize the disordered intermediate birnessite and the final crystalline phase formed as the final charge product. We expect the results will provide crucial insight into the development of aqueous, rechargeable battery systems utilizing MnO2. Figure 1 Operando Raman spectroscopy. (A) Individual Raman spectra, (B) contour map, and (C) corresponding voltage profile of the battery with a K-birnessite electrode. (D) Individual Raman spectra, (E) contour map, and (F) corresponding voltage profile of the battery with a K-birnessite with Bi2O3 electrode. Yadav, G. G.; Gallaway, J. W.; Turney, D. E.; Nyce, M.; Huang, J.; Wei, X.; Banerjee, S., Nature Communications 2017, 8, 14424. Dzieciuch, M. A.; Gupta, N.; Wroblowa, H. S., Journal of The Electrochemical Society 1988, 135 (10), 2415-2418. Wroblowa, H. S.; Gupta, N., Journal of Electroanalytical Chemistry and Interfacial Electrochemistry 1987, 238 (1), 93-102. Im, D.; Manthiram, A., Journal of The Electrochemical Society 2003, 150 (1), A68-A73. Gallaway, J. W.; Hertzberg, B. J.; Zhong, Z.; Croft, M.; Turney, D. E.; Yadav, G. G.; Steingart, D. A.; Erdonmez, C. K.; Banerjee, S., Power Sources 2016, 321, 135-142. Gallaway, J. W.; Yadav, G. G.; Turney, D. E.; Nyce, M.; Huang, J.; Chen-Wiegart, Y.-c. K.; Williams, G.; Thieme, J.; Okasinski, J. S.; Wei, X.; Banerjee, S., Journal of The Electrochemical Society 2018, 165 (13), A2935-A2947. Figure 1
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