Supporting Information Yb 0.0061 (6) 0.0093 (6) 0.0085 (6) 0.0017 (7) 0.000 0.000 Pd1 0.0048 (6) 0.0098 (5) 0.0099 (7) 0.000 0.000 0.0009 (4) Pd2 0.0061 (9) 0.0102 (9) 0.0058 (11) 0.000 0.000 −0.0016 (8) Ga1 0.0037 (6) 0.0091 (6) 0.0172 (8) 0.0003 (6) 0.0010 (8) 0.0004 (5) Ga2 0.0071 (11) 0.0103 (9) 0.0112 (12) 0.000 0.000 0.0001 (9) Ga3 0.015 (4) 0.014 (3) 0.021 (4) 0.003 (3) 0.000 0.000 Ga4 0.015 (6) 0.012 (5) 0.016 (6) 0.000 0.000 0.000 Yb(a) 0.0029 (10) 0.0097 (11) 0.0076 (10) 0.000 0.000 0.000 Ga3(a) 0.008 (4) 0.007 (3) 0.005 (4) −0.003 (3) 0.000 0.000 Ga3(b) 0.002 (4) 0.015 (4) 0.012 (4) −0.005 (3) 0.000 0.000 Ga4(a) 0.001 (3) 0.009 (3) 0.005 (3) −0.010 (3) 0.000

Synthetic control of the silver content in silver hollandite, AgxMn8O16, where the silver content ranges from 1.0 ≤ × ≤ 1.8 is demonstrated. This level of compositional control was enabled by the development of a lower temperature reflux based synthesis compared to the more commonly reported hydrothermal approach. Notably, the synthetic variance of the silver content was accompanied by a concomitant variance in crystallite size as well as surface area and particle size. In order to verify the retention of the hollandite structure, the first Rietveld analysis of silver hollandite was conducted on samples of varying composition. The impacts of silver content, crystallite size, surface area, and particle size on electrochemical reversibility were examined under cyclic voltammetry and battery testing.

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...

Single crystals of MAl2S4 (M = Mn2+, Fe2+, Co2+) were synthesized using the chemical vapor transport method and characterized using high-resolution synchrotron X-ray diffraction to determine the structure. All the compounds have a layered slab structure separated by a van der Waals gap, which results in highly two-dimensional magnetism. Magnetic susceptibility measurements indicate spin-glass behavior below T* values of ∼2 K, ∼ 10.5 K, and ∼5 K for MAl2S4 (M = Mn2+, Fe2+, Co2+), respectively, and heat capacity measurements indicate no long-range magnetic ordering observed down to 0.4 K. These results can be attributed primarily to site disorder due to mixing of M2+ and Al3+ ions (M = Mn2+, Fe2+, Co2+) and low dimensionality with geometrical frustration also playing a role. Interestingly, MnAl2S4, with almost isotropic S = 5/2 spin, has the highest frustration parameter among the series of compounds and is a possible candidate for a two-dimensional Heisenberg spin glass system.

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