Energy dispersive X-ray diffraction (EDXRD) with photons of high energy and high flux is used to map crystalline discharge products within alkaline AA cells following discharge at various rates: C/160, C/80, C/40, C/20, C/10, and C/5. During the study, the sealed cells are never opened and thus never exposed to air. The technique's resolution allows the various manganese oxide discharge products to be distinguished, which has previously proven difficult. In particular, colocalized Mn 3 O 4 (hausmannite) and ZnMn 2 O 4 (hetaerolite) phases are resolved at C/160, C/80, and C/40 rates. Following more rapid discharge at C/20, no hausmannite is observed: instead, two well-defined zones result, one consisting only of hetaerolite, and the other only of α-MnOOH (groutite), with a small transition region where both phases are detected. Modeling suggests the observed hetaerolite-groutite boundary positions are consistent with hetaerolite formation in regions of greater active material utilization. Radial hetaerolite and hausmannite profiles are calculated and found to be a function of the discharge current, which also determines discharge capacity. Results also show formation of a α-MnOOH phase from oxidation states MnO 1.7 to MnO 1.53 with relatively little γ-MnOOH character.The Zn-MnO 2 alkaline chemistry has been a staple of portable, high energy density batteries for half a century. Currently there is also interest in using this chemistry for large-scale storage, as the basis materials are safe and inexpensive at scale. At low depth of discharge (DOD) the ε(γ)-MnO 2 discharge product is MnOOH, which forms in the MnO 2 crystal lattice, creating a continuous, non-stoichiometric solid solution of MnO 2 and MnOOH. 1 However, as the MnOOH fraction increases and it becomes the majority component, an array of other lower oxides form such as Mn(OH) 2 and Mn 3 O 4 . While Mn(OH) 2 is considered a reversible product, meaning it can be reoxidized to MnO 2 , Mn 3 O 4 is not reversible and is therefore a discharge end-product. Mn 3 O 4 is known as hausmannite, a stable spinel-type material. Hetaerolite or ZnMn 2 O 4 is a spinel structure as is hausmannite, with a zinc atom replacing the divalent manganese atom. 2-7 In Zn-MnO 2 batteries, hetaerolite is also formed, as the anode is a source of zinc ions. 8-11 Both hausmannite and hetaerolite have resistivities six orders of magnitude higher than the active material MnO 2 , around 10 8 ohm-cm, and can lead to a loss of conductivity in the electrode and therefore failure. 12-14 Hetaerolite is known to limit MnO 2 discharge in the second electron regime, therefore limiting the capacity of Zn-MnO 2 batteries.The reaction pathways relating the myriad manganese oxide discharge products, listed in Table I, are not fully understood despite being a subject of interest for decades. The reasons for continued persistence toward eliminating this mystery are the desires to 1) increase cycle life of the system and to 2) increase available capacity for primary applications. When discharged cathodes...

Deeply penetrating white beam X-rays are used to detect zinc oxide precipitation in cycling alkaline batteries in real time.

Cyclic voltammetry of zinc plated from flowing alkaline zincate electrolyte with a bismuth additive showed a marked mass transport effect during metal layer deplating. This bismuth was added as Bi 2 O 3 and had a saturated concentration of 26 ppm bismuth. Using a small, transparent window flow cell the mechanism was studied in situ using synchrotron X-rays. X-ray microdiffraction revealed that the metal-electrolyte interface was bismuth rich, and bismuth behaved in a manner similar to a surfactant. Transmission X-ray microscopy revealed that in the presence of bismuth additive, 5 μm raised features on the metal layer were preferentially dissolved during deplating. However, macro-morphology experiments demonstrated that at 26 ppm a detrimental bismuth buildup occurred over many cycles. By reducing additive concentration to 3 ppm a metal layer was planarized compared to a no-additive control, while avoiding the bismuth buildup. These findings suggested that 3 ppm bismuth could be used to planarize zinc metal layers such as those in flow-assisted zinc batteries. However, concentration will need to be well-controlled.Zinc anode batteries are desirable for secondary energy storage due to the water-compatibility, natural abundance, safety, and high energy density of zinc. 1 Zinc anodes are found in several forms, which vary widely in design. Examples include the anodes in the following: metallic zinc flow battery hybrids, pelletized zinc-air battery/fuel cell hybrids, zinc-manganese dioxide batteries, and flow-assisted alkaline nickel-zinc batteries. 2-9 Systems in which a zinc anode is plated onto a current collector from electrolyte under forced convection have received attention for large scale applications, as in the flow-assisted nickel-zinc battery referenced above. 4 A key challenge for these systems is high aspect ratio zinc "dendrites" which progressively form during charge-discharge cycling of the zinc layer. Unless mitigated, these structures cross the electrolyte gap and short the cell.The micro-morphology of these progressive dendrites is generally the mossy form of zinc. Thus they are not like crystalline dendrites or diffusion limited aggregation structures except in their aspect ratio. Strategies to prevent dendrites during metal plating are the subject of frequent investigations, such as varying current density, electrolyte flow rate, and current waveforms. 10-12 These all aim to prevent initial formation of a high aspect ratio profile on the metal layer, as once that has occurred electric field effects will intensify dendrite formation. Additives or leveling agents also work in this way, suppressing deposition at asperity tips. 13 Screening electrolyte additives for use in flow-assisted batteries, we observed that ppm quantities of bismuth oxide provoked a substantial mass transport effect during anodic dissolution of zinc. This lead us to speculate that small quantities of bismuth oxide could act as a "reverse" leveling agent, planarizing zinc layers during discharge of the layer. The action of bismu...

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Compositions in the series Ni(2-x)Co(x)GeMo(3)N (0 < or = x < or = 2), Co(2)Ge(1-x)Ga(x)Mo(3)N (0 < x < or = 0.7), Co(2-x)Fe(x)GeMo(3)N (0 < or = x < or = 2), and Co(2-x)Fe(x)Ge(0.5)Ga(0.5)Mo(3)N (0 < or = x < or = 0.8) have been synthesized by the reductive nitridation of binary oxides and studied by appropriate combinations of magnetometry, transport measurements, neutron diffraction, and Mossbauer spectroscopy. All of these compositions adopt the cubic eta-carbide structure (a approximately 11.11 A) and show a resistivity of approximately 10(-3) Omega cm. No long-range magnetic order was observed in Ni(2-x)Co(x)GeMo(3)N, although evidence of spin freezing was observed in Co(2)GeMo(3)N. The introduction of gallium into this composition leads to the onset of antiferromagnetic ordering at 90 K in Co(2)Ge(0.3)Ga(0.7)Mo(3)N. The magnetic structure consists of an antiferromagnetic arrangement of ferromagnetic Co(4) groups, with an ordered magnetic moment of 0.48(9) micro(B) per cobalt atom. The same magnetic structure is found in Co(0.5)Fe(1.5)GeMo(3)N and Co(1.2)Fe(0.8)Ge(0.5)Ga(0.5)Mo(3)N. The former orders above room temperature with an average moment of 1.08(3) mu(B) per transition-metal site, and the latter at 228 K with an average moment of 1.17(4) micro(B) per site. The magnetic behavior of these compounds is discussed in terms of the electron count within each series.

MnO2-Zn alkaline batteries are one of the most common modern forms of primary battery, due to their relatively high energy density and low cost per kilowatt-hour. Additionally, unlike many other types of primary battery, alkaline cells can theoretically be recharged. Their low cost per kilowatt-hour makes them potentially ideal for applications such as sustainable energy storage or peak demand shaving. However, a phase transformation that occurs in MnO2 after reduction by more than one electron converts it into the electrochemically inactive Mn3O4 phase. This limits the total depth of discharge of the cell significantly. We report the synthesis of a novel electrode material, manganese-doped witherite, for rechargeable alkaline batteries produced by a simple hydrothermal process. The material has been studied via X-ray diffraction and electroanalytical techniques. We show that unaltered witherite has poor electrochemical properties, and that this new material has high capacity and rate capability, even under deep discharge conditions, superior to conventional manganese dioxide.

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