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Deliberately Designed Atomic-Level Silver Containing Inter-phase Results in Improved Rate Capability and Utilization of Silver Hollandite for Lithium-Ion Storage Paul F. Smith, Alexander B. Brady, Seung-Yong Lee, Andrea M. Bruck, Eric Dooryhee, Lijun Wu, Yimei Zhu, Kenneth J. Takeuchi, Esther S. Takeuchi, and Amy C. Marschilok ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b12307 • Publication Date (Web): 11 Dec 2017 Downloaded from http://pubs.acs.org on December 13, 2017

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ACS Applied Materials & Interfaces

Deliberately Designed Atomic-Level Silver Containing Interphase Results in Improved Rate Capability and Utilization of Silver Hollandite for Lithium-Ion Storage a

b

c

a

d

c

Paul F. Smith, Alexander B. Brady, Seung-Yong Lee, Andrea M. Bruck, Eric Dooryhee, Lijun Wu, Yimei Zhu, a,b* a,b,c* a,b,c* Kenneth J. Takeuchi, Esther S. Takeuchi, and Amy C. Marschilok a

c

Department of Chemistry, Stony Brook University, John S. Toll Rd, Stony Brook, NY 11794.

b

Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY 11794

c

Energy Sciences Directorate, Brookhaven National Laboratory, Upton NY 11973

d

Photon Science Division, National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY 11973

Keywords: alpha manganese oxide, Lithium battery cathode, Rate capability, Silver oxide, Reduction displacement Supporting Information Placeholder α-MnO2 structured materials are generally classified as semiconductors, thus we present a strategy to increase electrochemical utilization through design of a conductive material interface. Surface treatment of silver hol+ landite (AgxMn8O16) with Ag (Ag2O) provides significant benefit to the resultant electrochemistry, including a decreased charge transfer resistance, and a 2-fold increase in deliverable energy density at high rate. The improved function of this designed interface relative to conventional electrode fabrication strategies is highlighted.

ABSTRACT:

INTRODUCTION The development of energy storage technologies based on environmentally abundant, low toxicity metal centers, such as manganese (Mn) is desirable. In particular, the α-MnO2 1 structure (OMS-2 type ) is of interest due to its large capacity 2,3 to store cations within its 2x2 tunnels. Under defined application conditions, it has been shown that the structure can be largely retained throughout formation of Jahn-Teller dis3+ torted Mn by exhibiting anisotropic expansion in two of 4,5 three dimensions. 6

7

However, despite modifications of the identity and quantity 8,9 10 of tunnel cations, water content, and crystallite size, αMnO2 is generally classified as a semiconductor, as the 2 3 11 measured resistivity (10 -10 Ωcm) is largely unchanged. Thus α-MnO2 material has been studied for electrochemical energy storage by preparing electrodes using composite slurries with carbon and binder additives for improved electrical 12 conductivity and mechanical stability, respectively. These composite electrodes are necessary, but likely not sufficient, 13 for fully accessing all electroactive particles at high rate.

As an alternate strategy, our group has demonstrated electrical conductivity can be improved by taking advantage of reduction-displacement mechanisms in silver-ion containing materials. As example, the electrically insulating Ag2VO2PO4 14-16 cathode reduces to form a network of dispersed, conduc0 17,18 tive Ag particles that support fast electron transport. This 0 Ag network provides advantages which carbon alone cannot 17 + attain, as the Ag precursor is controlled and distributed on a smaller, atomic length scale as part of the inherent crystal

0

structure; i.e., Ag is generated with immediate proximity to each active material particle. For these reasons, prior research has attempted to apply the + Ag reduction displacement mechanism to α-MnO2 containing Agtunnel, silver hollandite (the structure is depicted in 10,19-25 Figure 1B). However, in Li batteries the formation of silver metal occurs only at the later stages of electrochemical 25 reduction (>4 e-/8 Mn in Mn8O16 nomenclature). Hence, the conductivity of the electrode in the early stages of lithiation are dominated by the connectivity of the composite electrode. This motivated improvement of electrical contact within the electrode through materials design. Recently, our group was the first to report Li electrochemistry of Ag2O-coated silver hollandite in carbon and binder24 free electrodes. That report highlighted considerable bene+ fits to electrochemistry in the presence of Ag on the silver hollandite surface (Agadsorbed): the capacity improved from 8 mAh/g (no Agadsorbed) to 120 mAh/g (with Agadsorbed). In this work, we highlight that benefits of the novel interfacial character gained from the presence of Agadsorbed remain important even in composite electrodes under discharge/charge conditions. The results highlight that conductive additives can be better positioned to provide electron access if designed on the atomic length scale. Due to the mass of the Ag2O component relative to the α-MnO2 component, there is no significant improvement on specific capacity under low rate discharge. However, improved transport properties are demonstrated with a 2-fold improvement in high-rate delivered energy density. Thus, despite the cost of silver, applications demanding high power may benefit from its enhanced interfacial properties.

EXPERIMENTAL Materials and Methods. Reagents were purchased commercially and used without further purification unless expressed otherwise. Powder X-ray diffraction data were taken on a Rigaku Smartlab diffractometer with Cu Kα radiation and Bragg-Brentano focusing geometry. Crystallite size was calculated by applying the Scherrer equation to the most prominent peak (~35°). A Thermo Scientific ICAP 6300 radial inductively coupled plasma optical emission spectrometer was used to determine quantitative Ag and Mn concentra-

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tions. Transmission electron microscopy was collected by a JEOL JEM 1400 microscope with Gatan CCD camera. HAADF-STEM images were taken on a double aberrationcorrected JEOL-ARM200CF microscope with a cold-field emission gun. The microscope is equipped with JEOL and Gatan HAADF detectors. Silver hollandite synthesis: AgxMn8O16 was prepared by adapting a previously reported method utilizing a reflux of 10 AgMnO4 and MnSO4 in 1:6 mol ratio. AgNO3 can be added to this bath to increase the tunnel silver (Agtunnel) content with negligible effect on crystallite size. Silver coating procedure: Silver coated samples (Agadsorbed) were prepared by refluxing a solution which was 0.1 M AgNO3 and 6000 ppm in AgxMn8O16 for 1 hour, followed by stirring overnight. This product was collected by filtration and dried in vacuo. Prior to electrode assembly, all samples were annealed in a dry room for 6 hr @ 300°C. Aqueous silver quantification. Following the reaction, 3M HCl was added to the filtrate to precipitate AgCl quantitatively from the remaining dissolved AgNO3. The resulting powder was isolated and weighed as AgCl. This procedure was calibrated and verified using a 0.1M AgNO3 solution.

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Where ߬= pulse length (600sec), VM/MB = molar vol3 ume/atomic weight (164 cm /g), S is electrode surface area 2 (1.266 cm ), and mB is mass of active material (0.0018-0.0019 g). ΔEs refers to the difference between the OCV before vs. 12 hrs. after the applied pulse; ΔEt refers to the difference between the voltage at the end of pulse vs. 12 hrs after the applied pulse. Eight-point data smoothing was applied to generate the GITT figure. Impedance data were collected over the frequency range of 100 kHz- 1 mHz.

RESULTS Synthesis, structural and compositional characterization of untreated and silver surface treated silver hollandite. The sample Ag1.20±0.03Mn8O16 was characterized as phase-pure by synchrotron-level powder x-ray diffraction (XPD), Figure 1A (ICSD-201792). Rietveld refinement (Table 1) with Rwp=3.52% reveals lattice parameters a=b= 9.784 and c= 2.8616, which are similar to previous reports with compa10,23 rable Ag content. A list of Rietveld fit parameters is provided in Table 1.

Synchrotron XPD and Refinement. Samples were packed in polyimide tubes for measurement. Powder X-Ray Diffraction was performed at the XPD-1 beamline at NSLS-II. The materials were tested using a wavelength of 0.2388 Angstroms and a 16-inch amorphous silicon flat panel with a CsI scintillator. An LaB6 standard was used to fit instrumental parameters and the wavelength. GSAS-II was used for image 26 integration and Rietveld Refinement. The background was fit with a 10 term Chebyshev polynomial, fit manually, and fixed throughout refinements in a method analogous to re27,28 cent reports. The occupancy of silver in the pristine material was fixed at the level measured by ICP-OES. By refinement the silver occupancy of the silver treated material (with Agtunnel) appeared to be higher. To better refine other values the silver occupancy was fixed at a silver occupancy we have previously observed and reported with consistent a/b parameters. The silver oxide contribution was fit with a fixed crystallite size of 2 nm, though the fraction was allowed to vary. These two assumptions match well with other data, as described in text. Electrode and cell assembly. Electrodes were prepared by casting slurries consisting of 85:10:5 (mass ratio) of active material: carbon: PVDF prepared using N-methyl pyrrolidinone onto aluminum foil. Either carbon black or a 1:1 (mass ratio) mixture of carbon black and graphite was used for the particular electrodes, as noted in the text. Coin type cells were assembled with 1 M LiPF6 in 3:7 (v:v) ethylene carbonate:dimethyl carbonate electrolyte, Li metal anodes and polypropylene separator membranes. Electrochemistry. Tests were performed on two electrode coin-type electrochemical cells using either a MACCOR Battery test system (cycling) or a Biologic (impedance) potentiostat. Rate capability tests discharged and charged the electrodes 5x each at 40, 100, 200, 400, 500 and 750 mA/g with 1 hr rest periods between each rate. Tests were terminated at 4 electrons or 1.8 V. Galvanostatic intermittent titration type (GITT) tests measured the voltage as a function of time for 10 minute pulses at 40 mA/g followed by 12 hr rest times. DLi 29 was calculated by the method of Weppner and Huggins:

Figure 1: Silver hollandite bulk structure. A: Synchrotron Xray powder diffraction of Ag1.2Mn8O16 with Rietveld fit. B: Ball and stick representation, ICSD- 201792. 30

Manganese oxides, including cryptomelane with α-MnO2 31 structure, are known to ion exchange the highest pKa H-OMn groups for Ag-O-Mn moieties in concentrated aqueous + Ag solution at pH 7. In this study, following reaction of Ag1.2Mn8O16 with excess AgNO3 in water, the solid product analyzed by inductively coupled plasma-optical emission spectroscopy (ICP-OES) showed a consistent increase of the relative Ag:Mn ratio to 2.1 ± 0.1 Ag:8Mn (ΔAg= 0.9±0.1). Sup+ plementing this dataset, the filtrate showed a decrease in Ag concentration (see Experimental), and SEM-EDS measurements (Figure S1) detected a similar range of (2.06 ≤ x ≤ 2.27) Ag:8Mn for the product material. a

Table 1. Rietveld refinement values for Ag1.2Mn8O16.


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ACS Applied Materials & Interfaces Variable

Value

Variable

Value

a=b c

9.784(4) 2.8616(4)

a=b

9.737(2)

c

2.8692(4)

Mn (x,y) O1 (x,y)

0.1504(5), 0.3301(6) 0.160(3), 0.196(1)

Mn (x,y)

0.1448(1), 0.3241(6)

O2 (x,y) Microstrain

0.172(3), 0.462(2) b 0.1%

O1 (x,y)

0.143(2), 0.204(1)

O2 (x,y)

0.171(3), 0.464(2)

Microstrain

2.3(3)%

Rwp

3.52%

Crystallite size

5.2(1)nm

Rwp 3.52% Crystallite size 5.23(6)nm (equatorial) a b Silver occupancy fixed at 0.60 from ICP-OES data; Parameter fixed at shown value. We performed Rietveld refinements of synchrotron based XPD diffraction data for the resulting Agadsorbed samples (Figure 2). Early iterations fixed all additional Ag content as 1) + discrete 2 nm Ag2O particles, and 2) surface exposed Ag modeled as additional Agtunnel, but the best fits found (Rwp=3.52%) incorporated a combination of both (Table 2). This suggests the added Ag distributes partially into the bulk as Agtunnel and partially as an Ag2O phase (confirmed by spec+ troscopy, vide infra). Thus, the amount of Ag in each phase can be quantified. The a=b lattice parameter is an indicator of the concentration of Agtunnel as the MnO2 octahedra contract slightly with increased silver ion content. For instance, prior literature has noted a=b values of 9.831 for 10 10 Ag1.15Mn8O16, 9.756 for Ag1.56Mn8O16, 9.738 for 23 20 Ag1.68Mn8O16, and 9.725 for Ag1.8Mn8O16. The contraction of the lattice parameter observed here (9.784 to 9.737) determined as a result of this refinement is consistent with the determined increase in Agtunnel content from Ag1.2Mn8O16 to Ag1.68Mn8O16. When allowed to vary, the optimized content for the remain+ ing Ag was established as 0.17Ag2O per Ag1.68Mn8O16. Therefore, the formula Ag1.68Mn8O16•0.17Ag2O is used through this manuscript to describe the silver surface treated (Agadsorbed) sample. The Ag:Mn ratio of this refined formula is precisely within the error of the ICP-OES (bulk) composition. All refinements indicated no significant change in crystallite size relative to the parent Ag1.2Mn8O16 material.

(equatorial) Phase fraction AgxMn8O16/Ag2O (w/w)%

95.1(5)%/4.9(5)%

Ag2O lattice parameter

4.87(2)

Ag2O crystallite size

2 nm

a

b b

Silver occupancy optimized at 0.83 and was fixed; Parameter fixed at shown value. The existence of the Ag2O phase is detected using infrared spectroscopy (Figure 3). Several features are observed which distinguish the Ag1.68Mn8O16•0.17Ag2O sample from the -1 -1 Ag1.2Mn8O16 material: 1) new peaks at 956 cm and 1382 cm , and 2) considerable broadening and damping of the -1 + Ag1.20Mn8O16 peak at 1100 cm . The Ag -O bond (e.g., Ag2O) is 32 expected to have two bands which, in the present system, -1 are masked by MnO6 vibrations below 600 cm . However, a -1 32 multi-phonon process is known at 951 cm , and bands re+ sulting from interactions of Ag with atmospheric water, 33,34 -1 oxygen and CO2 are known as broad features at 1070 cm -1 and 1380 cm , respectively. We interpret the FTIR as indica+ tive of the presence of Ag distinguishable from Agtunnel.

Figure 3. FTIR spectra of Ag1.2Mn8O16 (green) and Ag1.68Mn8O16•0.17Ag2O (blue). Insets show regions where new peaks appear for the Ag1.68Mn8O16•0.17Ag2O sample; baselines were adjusted for clarity. Figure 2. Synchrotron X-ray powder diffraction of Ag1.68Mn8O16•0.17Ag2O with Rietveld fit. Table 2. Rietveld refinement values for a Ag1.68Mn8O16•0.17Ag2O

Analysis by transmission electron microscopy (TEM) (Figure 4A-C) revealed the Ag1.68Mn8O16•0.17Ag2O sample to exhibit surface 1-3 nm particles which are absent from the Ag1.2Mn8O16 precursor. For most particles, selected area electron diffraction (SAED) patterns (Figure 4C-E) could be


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+

clearly indexed to Ag . We note that surface Ag is highly reactive and autoreduction under normal TEM conditions 35-37 has been noted in other studies. Some particles contained a 2.76 Ǻ d-spacing (Figure 4F-G) which does not correlate 0 with Ag and has two possible interpretations: 1) the most intense reflection for Ag2O [111]; and 2) the silver rich [211] plane of AgXMn8O16, (Figure S2). Based on the FTIR results, we attribute the particles with 2.76 Ǻ d-spacing to Ag2O.

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The materials were further evaluated with the galvanostatic 29 intermittent titration test (GITT) method , which utilizes short pulses of small currents to measure effective Li cation diffusion coefficients. Between 2.2-3.2 V, we measured these -10 -12 2 coefficients to be on the order of 10 -10 cm /s (Figure 5C). These numbers are within the range normally reported for -10 -11 potassium cryptomelane K0.06-0.11MnO2 (e.g., 10 -10 2 38-40 cm /s). Throughout the entire potential regime there is a 0.25 0.75 uniform increase ranging from 10 -10 for DLi effective in the Ag1.68Mn8O16•0.17Ag2O sample, equivalent to a 1.7-6 fold improvement relative to the uncoated material. This result was verified using alternating current impedance spectroscopy, as shown by Nyquist plot (Figure 5D). Impedance plots were fit using the model in Figure 5E. The Li batteries containing Ag1.2Mn8O16 + Ag1.68Mn8O16•0.17Ag2O samples achieved, by ~ 3 fold, lower charge transfer resistance relative to those containing Ag1.2Mn8O16 (Rct= 21Ω vs. 60Ω for the data in Figure 5D). The improved rate performance observed in the presence of Agadsorbed (Figure 5B) can thus be rationalized by lower charge transfer resistance and faster effective + Li diffusion (higher observed DLi) enabled by improved electron access.

Figure 4. Silver hollandite local structure and morphology. A: Representative image for Ag1.2Mn8O16. B: Representative image for Ag1.68Mn8O16•0.17Ag2O. C: Zoomed view on a ~2nm particle from the Ag1.68Mn8O16•0.17Ag2O sample. D-E: Single area electron diffraction on the particle from C. F: Surface analysis of Ag1.68Mn8O16•0.17Ag2O showing particles. G: Zoomed view on the white box from image F, showing both a 0 Ag particle (red circle), its SAED pattern (H) and an Ag2O particle with 2.76 Å d-spacing. Electrochemistry of silver treated and untreated silver hollandite. Galvanostatic testing experiments (5 cycles each at 6 rates, specifically 40, 100, 200, 400, 500 and 750 mA/g) for lithium based electrochemical cells containing Ag1.2Mn8O16 or Ag1.68Mn8O16•0.17Ag2O based electrodes prepared with carbon black indicated that Agadsorbed is beneficial, Figure 5A-B. When discharge rates are low (40 mA/g), there is no apparent effect of Agadsorbed on the loaded voltages (Figure 5A), as they remain constant under discharge to 2 molar electron equivalents for Ag1.2Mn8O16 and Ag1.68Mn8O16•0.17Ag2O, respectively. As lithiation rates are increased, the Ag1.68Mn8O16•0.17Ag2O electrode provides up to 2-fold higher delivered energy density (Figure 5A-B) with corresponding discharge capacities of 33 and 50 mAh/g for Ag1.2Mn8O16 and Ag1.68Mn8O16•0.17Ag2O under 500 mA/g, respectively. Comparing the energy density delivered at the lowest rate to that delivered at the highest rate gives an estimate of rate capability and capacity retention. Under the highest discharge rate, the Ag1.68Mn8O16•0.17Ag2O delivered 32% of its initial low rate capacity, where the uncoated Ag1.2Mn8O16 delivered only 13% (Figure 5A-B).

Figure 5. Electrochemistry of lithium based electrochemical cells containing Ag1.2Mn8O16 (green) or Ag1.68Mn8O16•0.17Ag2O (blue) based electrodes prepared with carbon black. (a) Five cycle voltage-capacity limited to 2 molar electron equivalents between 3.8-1.8V at 40 mA/g (dotted) and 500 mA/g (solid) rates. (b) The % of energy density difference (5 cycle average) as a function of rate. (c) Li diffusion constants obtained from GITT plots. (d) Nyquist plots taken at open circuit voltage (3.33 ± 0.13 V for Ag1.2Mn8O16, 3.22 ± 0.07 V for Ag1.68Mn8O16•0.17Ag2O). (e) Model used to fit impedance data. Characterization and electrochemistry of silver hollandite with varying Agtunnel content. To date, it has been a challenge to isolate solely the effect of Agtunnel on Li storage capability because efforts to vary Agtunnel often cause other modifications to the MnO2 parent material. The Ag content


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is most commonly tailored in synthesis by the AgMnO4:MnSO4 ratio, but this considerably also affects the 2 10 crystal size in approximately a linear relationship (R =0.75). Hence, while prior work demonstrates that superior Li storage results from materials with low Agtunnel content (e.g., 6fold improved capacity at 40 mA/g rates from Ag1.22Mn8O16 23 vs. Ag1.68Mn8O16) , the magnitude of this difference cannot be ascribed to the variable Agtunnel content alone, as crystallite size is also changing (5-8 vs. 10-20 nm crystallite sizes, for Ag1.22Mn8O16 vs. Ag1.68Mn8O16, respectively). In this manuscript Ag content was increased yet the crystallite size was unaffected. The powder x-ray diffraction data is provided in Figure S3. Galvanostatic testing of the lithium based electrochemical cells with Ag1.04Mn8O16 and Ag1.36Mn8O16 in carbon black containing electrodes showed similar capacities under discharge at 40 mA/g (Figure 6A). Following first discharge, these materials each cycled 4 electron equivalents with similar delivered energy densities for the two samples. However, under a higher current (100 mA/g), the impact of increased Agtunnel was apparent. While the Ag1.04Mn8O16 cell still cycled 4 Li above 1.8 V, the Ag1.36Mn8O16 cell delivered 17% less capacity (Figure 6B), illustrating that Agtunnel exhibits an overall negative impact on lithium ion storage under high rate conditions.

This observation further supports the notion that the bulk (Agtunnel) is filled preferentially to the surface (Agadsorbed) sites. On the basis of comparing Ag1.04Mn8O16 and Ag1.36Mn8O16, the presence of additional Agtunnel in α-MnO2 is expected to be overall detrimental to Li storage capacity. However, the results presented here demonstrate reduced cell-level impedance for the silver treated samples in spite of higher Agtunnel content. We note here an additional advantage of utilizing an active material which mediates its own inter-particle electrical contact. As-prepared silver hollandite which lacks surface conductive sites is dependent on additives, such as carbon, for electrical connectivity. As a consequence, the electrochemistry of silver hollandite is dependent on the formulation of the composite electrode, specifically, nature of the carbon additive. This is apparent in Figure 7C, which demonstrates that + silver hollandite/carbon black composites store more Li than silver hollandite/graphite composites. As suggested by TEM images (Figure 7A-B), this can be rationalized where smaller carbon black particles which enable greater electrical contact to the hollandite particles.

Figure 6. Representative or averaged electrochemistry for Ag1.04Mn8O16 (black) and Ag1.36Mn8O16 (red) with the same crystal size at 40mA/g (A) and 100 mA/g (B). Four cycles are depicted in each frame.

DISCUSSION The evidence for a smaller bulk a=b lattice parameter, com+ bined with evidence of Ag distinguishable from Agtunnel by TEM, ICP and FTIR, collectively suggest that with a second+ ary silver treatment, Ag distributes both into available bulk tunnel sites (~60% Agtunnel) and surface sites (~40% Agadsorbed) of Ag1.2Mn8O16, resulting in generation of Ag1.68Mn8O16•0.17Ag2O. On the basis of prior studies regard31,41 ing sorption of cations by MnO2 polymorphs we propose the following exchange reaction occurs both with surface terminated hydroxyls and hydronium ions trapped in bulk tunnel sites: +

+

Mn-OH + Ag → Mn-OAg + H

Prior literature has noted that empty tunnel sites are lowest + 19 in energy for binding Ag , likely because these sites match + 42 the 4-coordinate sphere of aqueous Ag . Consistent with this description, we were able to isolate Ag1.65Mn8O16 with very low amounts of surface coating by lowering the ratio of AgNO3:AgxMn8O16 in the ion exchange reaction (Figure S4).

Figure 7. (A-B) TEM images of uncoated Ag1.2Mn8O16 silver hollandite with graphite (A) and carbon black (B) additives. (C-D) Representative cycle 2-5 voltage-capacity traces between 3.8-1.8V at 40 mA/g rates for lithium based electrochemical cells containing uncoated (green) Ag1.2Mn8O16 (C) or silver treated (blue) Ag1.68Mn8O16•0.17Ag2O (D) based electrodes prepared with 1:1 graphite:carbon black mixtures (dotted line) or carbon black (solid line). (E) Nyquist plots over frequency range 100 kHz- 1mHz for coated (blue) and uncoated (green) silver hollandite electrodes constructed with carbon black (solid) and 1:1 graphite:carbon black mixtures (dotted).



In contrast, the use of Agadsorbed reduces the impact of the carbon additive and provides the material with a surfacemounted, small sized conductive additive which can more effectively electrically connect each particle within the electrode. While the type of carbon used has a profound effect on the functional capacity for the unmodified Ag1.2Mn8O16 material, the silver surface treated (Agadsorbed) Ag1.68Mn8O16•0.17Ag2O sample delivers an energy density independent of carbon type (Figure 7D). Impedance plots (Figure 7E) indicate that Agadsorbed becomes even more beneficial at decreasing charge transfer resistance when carbon connectivity is poorer (Rct=55 vs. 204 Ω). The effect of Agadsorbed is therefore shown to approach the objective of 43 wiring every particle within a mesoscale electrode.

CONCLUSION We have shown here that the nature and location of conductive additive show significant effect on battery relevant electrochemistry. This is demonstrated on the atomic level using + Ag as the additive and α-MnO2 structured Ag1.2Mn8O16 as + the active material. Specifically, Ag distributed on the material surface (Agadsorbed) results in improvement in rate capability by up to a factor of 2. Conductive additives are necessary for full utilization of insulating or semiconducting active materials for energy storage. This work indicates that atomic scale distribution of conductive additives through deliberate design of composite materials can be an effective method to move toward full utilization of active materials.

ASSOCIATED CONTENT Supporting Information: Figures showing laboratory diffraction data, SEM-EDS, the silver-rich lattice plane of silver hollandite, and TEM images indicating bulk sites fill preferentially. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION *Corresponding Authors: (KJT) [email protected]; (EST) [email protected]; (ACM) [email protected].

ACKNOWLEDGMENT This work was supported as part of the Center for Mesoscale Transport Properties, an Energy Frontier Research Center supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences via grant #DE-SC0012673. This research used beamline 28-ID-2 X-ray Powder Diffraction(XPD) of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. The authors thank Chung ChuehCheng for assistance with TEM measurements and Jianping Huang for discussions. The authors declare no competing financial interests.

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REFERENCES (1) Suib, S. L. Porous Manganese Oxide Octahedral Molecular Sieves and Octahedral Layered Materials. Acc. Chem. Res. 2008, 41, 479-487. (2) Thackeray, M. M. Manganese Oxides for Lithium Batteries. Prog. Solid State Chem. 1997, 25, 1-71. (3) Johnson, C. S.; Dees, D. W.; Mansuetto, M. F.; Thackeray, M. M.; Vissers, D. R.; Argyriou, D.; Loong, C. K.; Christensen, L. Structural and Electrochemical Studies of α-Manganese Dioxide (α-MnO2). J. Power Sources 1997, 68, 570-577. (4) Yang, Z.; Trahey, L.; Ren, Y.; Chan, M. K. Y.; Lin, C.; Okasinski, J.; Thackeray, M. M. In Situ High-Energy Synchrotron X-ray Diffraction Studies and First Principles Modeling of αMnO2 Electrodes in Li-O2 and Li-ion Coin Cells. J. Mater. Chem. A 2015, 3, 7389-7398. (5) Yuan, Y.; Nie, A.; Odegard, G. M.; Xu, R.; Zhou, D.; Santhanagopalan, S.; He, K.; Asayesh-Ardakani, H.; Meng, D. D.; Klie, R. F.; Johnson, C.; Lu, J.; Shahbazian-Yassar, R. Asynchronous Crystal Cell Expansion During Lithiation of K+Stabilized α-MnO2. Nano Lett. 2015, 15, 2998-3007. (6) Poyraz, A. S.; Huang, J.; Cheng, S.; Wu, L.; Tong, X.; Zhu, Y.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Tunnel Structured α-MnO2 with Different Tunnel Cations (H+, K+, Ag+) as Cathode Materials in Rechargeable Lithium Batteries: The Role of Tunnel Cation on Electrochemistry. J. Electrochem. Soc. 2017, 164, A1983-A1990. (7) Yuan, Y.; Zhan, C.; He, K.; Chen, H.; Yao, W.; Sharifi-Asl, S.; Song, B.; Yang, Z.; Nie, A.; Luo, X.; Wang, H.; Wood, S. M.; Amine, K.; Islam, M. S.; Lu, J.; Shahbazian-Yassar, R. The Influence of Large Cations on the Electrochemical Properties of Tunnel-Structured Metal Oxides. Nat. Commun. 2016, 7, 13374. (8) Poyraz, A. S.; Huang, J.; Zhang, B.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Synthesis of Cation and Water Free Cryptomelane Type OMS-2 Cathode Materials: The Impact of Tunnel Water on Electrochemistry. MRS Adv. 2017, 2, 407412. (9) Yang, Z.; Ford, D. C.; Park, J. S.; Ren, Y.; Kim, S.; Kim, H.; Fister, T. T.; Chan, M. K. Y.; Thackeray, M. M. Probing the Release and Uptake of Water in α-MnO2·xH2O. Chem. Mater. 2017, 29, 1507-1517. (10) Takeuchi, K. J.; Yau, S. Z.; Menard, M. C.; Marschilok, A. C.; Takeuchi, E. S. Synthetic Control of Composition and Crystallite Size of Silver Hollandite, AgxMn8O16: Impact on Electrochemistry. ACS Appl. Mater. Interfaces 2012, 4, 55475554. (11) De Guzman, R. N.; Awaluddin, A.; Shen, Y.-F.; Tian, Z. R.; Suib, S. L.; Ching, S.; O'Young, C.-L. Electrical Resistivity Measurements on Manganese Oxides with Layer and Tunnel Structures: Birnessites, Todorokites, and Cryptomelanes. Chem. Mater. 1995, 7, 1286-1292. (12) Talaie, E.; Bonnick, P.; Sun, X.; Pang, Q.; Liang, X.; Nazar, L. F. Methods and Protocols for Electrochemical Energy Storage Materials Research. Chem. Mater. 2017, 29, 90-105. (13) Durham, J. L.; Poyraz, A. S.; Takeuchi, E. S.; Marschilok, A. C.; Takeuchi, K. J. Impact of Multifunctional Bimetallic Materials on Lithium Battery Electrochemistry. Acc. Chem. Res. 2016, 49, 1864-1872. (14) Kirshenbaum, K. C.; Bock, D. C.; Zhong, Z.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. In situ Profiling of Lithium/Ag2VP2O8 Primary Batteries Using Energy Dispersive Xray Diffraction. Phys. Chem. Chem. Phys. 2014, 16, 9138-9147. (15) Kirshenbaum, K.; Bock, D. C.; Lee, C.-Y.; Zhong, Z.; Takeuchi, K. J.; Marschilok, A. C.; Takeuchi, E. S. In Situ Visualization of Li/Ag2VP2O8 Batteries Revealing RateDependent Discharge Mechanism. Science 2015, 347, 149-154.


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(16) Kirshenbaum, K. C.; Bock, D. C.; Brady, A. B.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Electrochemical Reduction of an Ag2VO2PO4 Particle: Dramatic Increase of Local Electronic Conductivity. Phys. Chem. Chem. Phys. 2015, 17, 11204-11210. (17) Bock, D. C.; Bruck, A. M.; Pelliccione, C. J.; Zhang, Y.; Takeuchi, K. J.; Marschilok, A. C.; Takeuchi, E. S. Li/Ag2VO2PO4 Batteries: the Roles of Composite Electrode Constituents on Electrochemistry. RSC Adv. 2016, 6, 106887106898. (18) Knehr, K. W.; West, A. C. Theoretical Considerations for Improving the Pulse Power of a Battery through the Addition of a Second Electrochemically Active Material. J. Electrochem. Soc. 2016, 163, A1576-A1583. (19) Huang, Z.; Gu, X.; Cao, Q.; Hu, P.; Hao, J.; Li, J.; Tang, X. Catalytically Active Single-Atom Sites Fabricated from Silver Particles. Angew. Chem. Int. Ed. 2012, 51, 4198-4203. (20) Chang, F. M.; Jansen, M. Ag1.8Mn8O16: Square Planar Coordinated Ag+ Ions in the Channels of a Novel Hollandite Variant. Angew. Chem. Int. Ed. 1984, 23, 906-907. (21) Zhu, S.; Marschilok, A. C.; Lee, C.-Y.; Takeuchi, E. S.; Takeuchi, K. J. Synthesis and Electrochemistry of Silver Hollandite. Electrochem. Solid-State Lett. 2010, 13, A98. (22) Takeuchi, K. J.; Yau, S. Z.; Subramanian, A.; Marschilok, A. C.; Takeuchi, E. S. The Electrochemistry of Silver Hollandite Nanorods, AgxMn8O16: Enhancement of Electrochemical Battery Performance via Dimensional and Compositional Control. J. Electrochem. Soc. 2013, 160, A3090-A3094. (23) Wu, L.; Xu, F.; Zhu, Y.; Brady, A. B.; Huang, J.; Durham, J. L.; Dooryhee, E.; Marschilok, A. C.; Takeuchi, E. S.; Takeuchi, K. J. Structural Defects of Silver Hollandite, AgxMn8Oy, Nanorods: Dramatic Impact on Electrochemistry. ACS Nano 2015, 9, 8430-8439. (24) Zhang, B.; Smith, P. F.; Lee, S.-Y.; Wu, L.; Zhu, Y.; Takeuchi, E. S.; Marschilok, A. C.; Takeuchi, K. J. Tailoring the Ag+ Content within the Tunnels and on the Exposed Surfaces of α-MnO2 Nanowires: Impact on Impedance and Electrochemistry. J. Electrochem. Soc. 2017, 164, A6163-A6170. (25) Huang, J.; Poyraz, A. S.; Lee, S.-Y.; Wu, L.; Zhu, Y.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. SilverContaining α-MnO2 Nanorods: Electrochemistry in Na-Based Battery Systems. ACS Appl. Mater. Interfaces 2017, 9, 43334342. (26) Toby, B. H.; Von Dreele, R. B. GSAS-II: the Genesis of a Modern Open-Source All Purpose Crystallography Software Package. J. Appl. Crystallogr. 2013, 46, 544-549. (27) Perera, S. S.; Amarasinghe, D. K.; Dissanayake, K. T.; Rabuffetti, F. A. Average and Local Crystal Structure of βEr:Yb:NaYF4 Upconverting Nanocrystals Probed by X-ray Total Scattering. Chem. Mater. 2017, 29, 6289-6297. (28) Karmaoui, M.; Ramana, E. V.; Tobaldi, D. M.; Lajaunie, L.; Graca, M. P.; Arenal, R.; Seabra, M. P.; Labrincha, J. A.; Pullar, R. C. High Dielectric Constant and Capacitance in Ultrasmall (2.5 nm) SrHfO3 Perovskite Nanoparticles Produced in a Low Temperature Non-Aqueous Sol-gel Route. RSC Adv. 2016, 6, 51493-51502. (29) Weppner, W.; Huggins, R. A. Determination of the Kinetic Parameters of Mixed‐Conducting Electrodes and Application to the System Li3Sb. J. Electrochem. Soc. 1977, 124, 1569-1578.

(30) Sarı, A.; Tüzen, M. Adsorption of Silver from Aqueous Solution onto Raw Vermiculite and Manganese Oxide-Modified Vermiculite. Microporous Mesoporous Mater. 2013, 170, 155163. (31) Ravikumar, R.; Fuerstenau, D. W. Silver Sorption by Manganese Oxide. Mater. Res. Soc. Symp. Proc. 1996, 432. (32) Waterhouse, G. I. N.; Bowmaker, G. A.; Metson, J. B. The Thermal Decomposition of Silver (I, III) Oxide: A Combined XRD, FT-IR and Raman Spectroscopic Study. Phys. Chem. Chem. Phys. 2001, 3, 3838-3845. (33) Slager, T. L.; Lindgren, B. J.; Mallmann, A. J.; Greenler, R. G. Infrared Spectra of the Oxides and Carbonates of Silver. J. Phys. Chem. 1972, 76, 940-943. (34) McIntosh, D.; Ozin, G. A. Metal Atom Chemistry and Surface Chemistry. Dioxygensilver Ag+,O2-, and Tetraoxygensilver, Ag+,O4-, Reactive Intermediates in the Silver Atom-Dioxygen System. Relevance to Surface Chemistry. Inorg. Chem. 1977, 16, 59-63. (35) Woehl, T. J.; Evans, J. E.; Arslan, I.; Ristenpart, W. D.; Browning, N. D. Direct in Situ Determination of the Mechanisms Controlling Nanoparticle Nucleation and Growth. ACS Nano 2012, 6, 8599-8610. (36) Longo, E.; Cavalcante, L. S.; Volanti, D. P.; Gouveia, A. F.; Longo, V. M.; Varela, J. A.; Orlandi, M. O.; Andrés, J. Direct in Situ Observation of the Electron-Driven Synthesis of Ag Filaments on α-Ag2WO4 Crystals. Sci. Rep. 2013, 3, 1676. (37) Zhang, H.; Wang, G.; Chen, D.; Lv, X.; Li, J. Tuning Photoelectrochemical Performances of Ag−TiO2 Nanocomposites via Reduction/Oxidation of Ag. Chem. Mater. 2008, 20, 65436549. (38) Byles, B. W.; Palapati, N. K. R.; Subramanian, A.; Pomerantseva, E. The Role of Electronic and Ionic Conductivities in the Rate Performance of Tunnel Structured Manganese Oxides in Li-ion batteries. APL Mater. 2016, 4, 46108-46108. (39) Bach, S.; Pereira-Ramos, J. P.; Baffier, N. A New MnO2 Tunnel Related Phase as Host Lattice for Li Intercalation. Solid State Ionics 1995, 80, 151-158. (40) Poyraz, A. S.; Huang, J.; Pelliccione, C. J.; Tong, X.; Cheng, S.; Wu, L.; Zhu, Y.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Synthesis of Cryptomelane Type α-MnO2 (KxMn8O16) Cathode Materials with Tunable K+ Content: the Role of Tunnel Cation Concentration on Electrochemistry. J. Mater. Chem.A 2017, 5, 16914-16928 (41) Pretorius, P. J.; Linder, P. W. The Adsorption Characteristics of δ-Manganese Dioxide: a Collection of Diffuse Double Layer Constants for the Adsorption of H+, Cu2+, Ni2+, Zn2+, Cd2+ and Pb2+. Appl. Geochem. 2001, 16, 1067-1082. (42) Texter, J.; Hastreiter, J. J.; Hall, J. L. Spectroscopic Confirmation of the Tetrahedral Geometry of Tetraaquasilver(+) Ion (Ag(H2O)4+). J. Phys. Chem. 1983, 87, 4690-4693. (43) Dudney, N. J.; Li, J. Using All Energy in a Battery. Science 2015, 347, 131-132.



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References (1)

Suib, S. L. Porous Manganese Oxide Octahedral Molecular Sieves and Octahedral Layered Materials. Accounts of Chemical Research 2008, 41, 479-487. (2) Thackeray, M. M. Manganese oxides for lithium batteries. Progress in Solid State Chemistry 1997, 25, 1-71. (3) Johnson, C. S.; Dees, D. W.; Mansuetto, M. F.; Thackeray, M. M.; Vissers, D. R.; Argyriou, D.; Loong, C. K.; Christensen, L. Structural and electrochemical studies of α-manganese dioxide (α-MnO2). Journal of Power Sources 1997, 68, 570-577. (4) Yang, Z.; Trahey, L.; Ren, Y.; Chan, M. K. Y.; Lin, C.; Okasinski, J.; Thackeray, M. M. In situ high-energy synchrotron X-ray diffraction studies and first principles modeling of [small alpha]MnO2 electrodes in Li-O2 and Li-ion coin cells. Journal of Materials Chemistry A 2015, 3, 7389-7398. (5) Yuan, Y.; Nie, A.; Odegard, G. M.; Xu, R.; Zhou, D.; Santhanagopalan, S.; He, K.; Asayesh-Ardakani, H.; Meng, D. D.; Klie, R. F.; Johnson, C.; Lu, J.; Shahbazian-Yassar, R. Asynchronous Crystal Cell Expansion during Lithiation of K+-Stabilized α-MnO2. Nano Letters 2015, 15, 2998-3007. (6) Poyraz, A. S.; Huang, J.; Cheng, S.; Wu, L.; Tong, X.; Zhu, Y.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Tunnel Structured α-MnO2 with Different Tunnel Cations (H+, K+, Ag+) as Cathode Materials in Rechargeable Lithium Batteries: The Role of Tunnel Cation on Electrochemistry. Journal of The Electrochemical Society 2017, 164, A1983-A1990. (7) Yuan, Y.; Zhan, C.; He, K.; Chen, H.; Yao, W.; Sharifi-Asl, S.; Song, B.; Yang, Z.; Nie, A.; Luo, X.; Wang, H.; Wood, S. M.; Amine, K.; Islam, M. S.; Lu, J.; Shahbazian-Yassar, R. The influence of large cations on the electrochemical properties of tunnel-structured metal oxides. Nature Communications 2016, 7, 13374. (8) Poyraz, A. S.; Huang, J.; Zhang, B.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Synthesis of Cation and Water Free Cryptomelane Type OMS-2 Cathode Materials: The Impact of Tunnel Water on Electrochemistry. MRS Advances 2017, 2, 407-412. (9) Yang, Z.; Ford, D. C.; Park, J. S.; Ren, Y.; Kim, S.; Kim, H.; Fister, T. T.; Chan, M. K. Y.; Thackeray, M. M. Probing the Release and Uptake of Water in α-MnO2·xH2O. Chemistry of Materials 2017, 29, 1507-1517. (10) Takeuchi, K. J.; Yau, S. Z.; Menard, M. C.; Marschilok, A. C.; Takeuchi, E. S. Synthetic control of composition and crystallite size of silver hollandite, Ag xMn 8O 16: Impact on electrochemistry. ACS Applied Materials and Interfaces 2012, 4, 5547-5554. (11) De Guzman, R. N.; Awaluddin, A.; Shen, Y.-F.; Tian, Z. R.; Suib, S. L.; Ching, S.; O'Young, C.-L. Electrical Resistivity Measurements on Manganese Oxides with Layer and Tunnel Structures: Birnessites, Todorokites, and Cryptomelanes. Chemistry of Materials 1995, 7, 1286-1292. (12) Talaie, E.; Bonnick, P.; Sun, X.; Pang, Q.; Liang, X.; Nazar, L. F. Methods and Protocols for Electrochemical Energy Storage Materials Research. Chemistry of Materials 2017, 29, 90-105. (13) Durham, J. L.; Poyraz, A. S.; Takeuchi, E. S.; Marschilok, A. C.; Takeuchi, K. J. Impact of Multifunctional Bimetallic Materials on Lithium Battery Electrochemistry. Accounts of Chemical Research 2016, 49, 1864-1872. (14) Kirshenbaum, K. C.; Bock, D. C.; Zhong, Z.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. In situ profiling of lithium/Ag2VP2O8 primary batteries using energy dispersive X-ray diffraction. Physical Chemistry Chemical Physics 2014, 16, 9138-9147. (15) Kirshenbaum, K.; Bock, D. C.; Lee, C.-Y.; Zhong, Z.; Takeuchi, K. J.; Marschilok, A. C.; Takeuchi, E. S. In situ visualization of Li/Ag2VP2O8 batteries revealing rate-dependent discharge mechanism. Science 2015, 347, 149-154. (16) Kirshenbaum, K. C.; Bock, D. C.; Brady, A. B.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Electrochemical reduction of an Ag2VO2PO4 particle: dramatic increase of local electronic conductivity. Physical Chemistry Chemical Physics 2015, 17, 11204-11210. ACS Paragon Plus Environment

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(17) Bock, D. C.; Bruck, A. M.; Pelliccione, C. J.; Zhang, Y.; Takeuchi, K. J.; Marschilok, A. C.; Takeuchi, E. S. Li/Ag2VO2PO4 batteries: the roles of composite electrode constituents on electrochemistry. RSC Advances 2016, 6, 106887-106898. (18) Knehr, K. W.; West, A. C. Theoretical Considerations for Improving the Pulse Power of a Battery through the Addition of a Second Electrochemically Active Material. Journal of The Electrochemical Society 2016, 163, A1576-A1583. (19) Huang, Z.; Gu, X.; Cao, Q.; Hu, P.; Hao, J.; Li, J.; Tang, X. Catalytically active singleatom sites fabricated from silver particles. Angewandte Chemie - International Edition 2012, 51, 41984203. (20) Chang, F. M.; Jansen, M. Ag1.8Mn8O16: Square Planar Coordinated Ag⊕ Ions in the Channels of a Novel Hollandite Variant. Angewandte Chemie International Edition in English 1984, 23, 906-907. (21) Zhu, S.; Marschilok, A. C.; Lee, C.-Y.; Takeuchi, E. S.; Takeuchi, K. J. Synthesis and Electrochemistry of Silver Hollandite. Electrochemical and Solid-State Letters 2010, 13, A98. (22) Takeuchi, K. J.; Yau, S. Z.; Subramanian, a.; Marschilok, a. C.; Takeuchi, E. S. The Electrochemistry of Silver Hollandite Nanorods, AgxMn8O16: Enhancement of Electrochemical Battery Performance via Dimensional and Compositional Control. Journal of The Electrochemical Society 2013, 160, A3090-A3094. (23) Wu, L.; Xu, F.; Zhu, Y.; Brady, A. B.; Huang, J.; Durham, J. L.; Dooryhee, E.; Marschilok, A. C.; Takeuchi, E. S.; Takeuchi, K. J. Structural Defects of Silver Hollandite, AgxMn8Oy, Nanorods: Dramatic Impact on Electrochemistry. ACS Nano 2015, 9, 8430-8439. (24) Zhang, B.; Smith, P. F.; Lee, S.-Y.; Wu, L.; Zhu, Y.; Takeuchi, E. S.; Marschilok, A. C.; Takeuchi, K. J. Tailoring the Ag+ Content within the Tunnels and on the Exposed Surfaces of α-MnO2 Nanowires: Impact on Impedance and Electrochemistry. Journal of The Electrochemical Society 2017, 164, A6163-A6170. (25) Huang, J.; Poyraz, A. S.; Lee, S.-Y.; Wu, L.; Zhu, Y.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Silver-Containing α-MnO2 Nanorods: Electrochemistry in Na-Based Battery Systems. ACS Applied Materials & Interfaces 2017, 9, 4333-4342. (26) Toby, B. H.; Von Dreele, R. B. GSAS-II: the genesis of a modern open-source all purpose crystallography software package. Journal of Applied Crystallography 2013, 46, 544-549. (27) Perera, S. S.; Amarasinghe, D. K.; Dissanayake, K. T.; Rabuffetti, F. A. Average and Local Crystal Structure of β-Er:Yb:NaYF4 Upconverting Nanocrystals Probed by X-ray Total Scattering. Chemistry of Materials 2017, 29, 6289-6297. (28) Karmaoui, M.; Ramana, E. V.; Tobaldi, D. M.; Lajaunie, L.; Graca, M. P.; Arenal, R.; Seabra, M. P.; Labrincha, J. A.; Pullar, R. C. High dielectric constant and capacitance in ultrasmall (2.5 nm) SrHfO3 perovskite nanoparticles produced in a low temperature non-aqueous sol-gel route. RSC Advances 2016, 6, 51493-51502. (29) Weppner, W.; Huggins, R. A. Determination of the Kinetic Parameters of Mixed‐ Conducting Electrodes and Application to the System Li3Sb. Journal of The Electrochemical Society 1977, 124, 1569-1578. (30) Sarı, A.; Tüzen, M. Adsorption of silver from aqueous solution onto raw vermiculite and manganese oxide-modified vermiculite. Microporous and Mesoporous Materials 2013, 170, 155-163. (31) Ravikumar, R.; Fuerstenau, D. W. Silver Sorption by Manganese Oxide. MRS Proceedings 1996, 432. (32) Waterhouse, G. I. N.; Bowmaker, G. A.; Metson, J. B. The thermal decomposition of silver (I, III) oxide: A combined XRD, FT-IR and Raman spectroscopic study. Physical Chemistry Chemical Physics 2001, 3, 3838-3845. (33) Slager, T. L.; Lindgren, B. J.; Mallmann, A. J.; Greenler, R. G. Infrared spectra of the oxides and carbonates of silver. The Journal of Physical Chemistry 1972, 76, 940-943.


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(34) McIntosh, D.; Ozin, G. A. Metal atom chemistry and surface chemistry. 1. Dioxygensilver Ag+,O2-, and tetraoxygensilver, Ag+,O4-, reactive intermediates in the silver atomdioxygen system. Relevance to surface chemistry. Inorganic Chemistry 1977, 16, 59-63. (35) Woehl, T. J.; Evans, J. E.; Arslan, I.; Ristenpart, W. D.; Browning, N. D. Direct in Situ Determination of the Mechanisms Controlling Nanoparticle Nucleation and Growth. ACS Nano 2012, 6, 8599-8610. (36) Longo, E.; Cavalcante, L. S.; Volanti, D. P.; Gouveia, A. F.; Longo, V. M.; Varela, J. A.; Orlandi, M. O.; Andrés, J. Direct in situ observation of the electron-driven synthesis of Ag filaments on α-Ag2WO4 crystals. Scientific Reports 2013, 3, 1676-1676. (37) Zhang, H.; Wang, G.; Chen, D.; Lv, X.; Li, J. Tuning Photoelectrochemical Performances of Ag−TiO2 Nanocomposites via Reduction/Oxidation of Ag. Chemistry of Materials 2008, 20, 6543-6549. (38) Byles, B. W.; Palapati, N. K. R.; Subramanian, A.; Pomerantseva, E. The role of electronic and ionic conductivities in the rate performance of tunnel structured manganese oxides in Liion batteries. APL Materials 2016, 4, 46108-46108. (39) Bach, S.; Pereira-Ramos, J. P.; Baffier, N. A new MnO2 tunnel related phase as host lattice for Li intercalation. Solid State Ionics 1995, 80, 151-158. (40) Poyraz, A. S.; Huang, J.; Pelliccione, C. J.; Tong, X.; Cheng, S.; Wu, L.; Zhu, Y.; Marschilok, A. C.; Takeuchi, K. J.; Takeuchi, E. S. Synthesis of cryptomelane type [small alpha]-MnO2 (KxMn8O16) cathode materials with tunable K+ content: the role of tunnel cation concentration on electrochemistry. Journal of Materials Chemistry A 2017, 5, 16914-16928. (41) Pretorius, P. J.; Linder, P. W. The adsorption characteristics of δ-manganese dioxide: a collection of diffuse double layer constants for the adsorption of H+, Cu2+, Ni2+, Zn2+, Cd2+ and Pb2+. Applied Geochemistry 2001, 16, 1067-1082. (42) Texter, J.; Hastreiter, J. J.; Hall, J. L. Spectroscopic confirmation of the tetrahedral geometry of tetraaquasilver(+) ion (Ag(H2O)4+). The Journal of Physical Chemistry 1983, 87, 46904693. (43) Dudney, N. J.; Li, J. Using all energy in a battery. Science 2015, 347, 131 LP-132.


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