We report the discovery of a new superprotonic compound, Cs 7 (H 4 PO 4 )(H 2 PO 4 ) 8 , or CPP, which forms at elevated temperatures from the reaction of CsH 2 PO 4 and CsH 5 (PO 4 ) 2 . The structure, solved using high-temperature single-crystal X-ray diffraction and confirmed by high-temperature 31 P NMR spectroscopy, crystallizes in space group Pm3̅ n and has a lattice constant of 20.1994(9) Å at 130 °C. The unit cell resembles a 4 × 4 × 4 superstructure of superprotonic CsH 2 PO 4 , but features an extraordinary chemical moiety, rotationally disordered H 4 PO 4 + cations, which periodically occupy one of every eight cation sites. The influence of this remarkable cation on the structure, thermodynamics, and proton transport properties of the CPP phase is discussed. Notably, CPP forms at a temperature of 90 °C, much lower than the superprotonic transition temperature of 228 °C of CsH 2 PO 4 , and the compound does not appear to have an ordered, low-temperature form. Under nominally dry conditions, the material is stable against dehydration to ∼151 °C, and this results in a particularly wide region of stability of a superprotonic material in the absence of active humidification. The conductivity of Cs 7 (H 4 PO 4 )(H 2 PO 4 ) 8 is moderate, 5.8 × 10 −4 S cm −1 at 140 °C, but appears nevertheless facilitated by polyanion (H 2 PO 4 − ) group reorientation.

CsH 2 PO 4 has garnered interest as a protonconducting electrolyte due to its exceptional conductivity at intermediate temperatures (228−300 °C) at which it adopts a cubic structure with a high degree of disorder. Here, through a study of mixtures of CsH 2 PO 4 (CDP) and CsH 5 (PO 4 ) 2 , the cubic phase was discovered to form solid solutions of composition [Cs 1−x H x ]H 2 PO 4 , with x extending to at least 2/9. A phase diagram of the composition space (1−x)CsH 2 PO 4 − xH 3 PO 4 , 0 ≤ x ≤ 2/9 was developed through thermal analysis, high-temperature in situ X-ray diffraction experiments, and variable-temperature NMR spectroscopy. At temperatures above about 90 °C, monoclinic, stoichiometric CDP exists in equilibrium with Cs 7 (H 4 PO 4 )-(H 2 PO 4 ) 8 . These two phases displayed eutectoid behavior, with a eutectoid reaction temperature and composition of 155 °C and x = 0.18, respectively, to form cubic [Cs 1−x H x ]H 2 PO 4 . The structural studies revealed, rather remarkably, that the cubic phase accommodates vacancies on the cation site that are charge-balanced by excess protons, where the latter are chemically associated with phosphate groups. The conductivities of cubic phases of various compositions, measured by impedance spectroscopy, are comparable to that of CDP. The excellent proton conductivities of off-stoichiometric, cubic [Cs 1−x H x ]H 2 PO 4 at temperatures well below the superprotonic transition of stoichiometric CDP present the opportunity to extend the low-temperature operating limit of CDP-based devices. More generally, the off-stoichiometric phase behavior demonstrated here introduces a new approach for the modification of superprotonic solid acid compounds.

Highly oriented columnar nanostructures of tin dioxide (SnO2) and a composite tin dioxide material with a thin titanium dioxide coating (SnO2–TiO2) are fabricated using aerosol chemical vapor deposition (ACVD) and are utilized as high‐capacity anode materials in lithium‐ion batteries. The SnO2 nanostructures exhibit a specific capacity of 445 mAh g−1 after 100 cycles at a rate of 1 C, but experience substantial capacity fade at a charge rate of 2 C, and a capacity of 251 mAh g−1 after 100 cycles. To enhance the capacity retention a coating of TiO2 is applied to the electrodes. Comparatively, the SnO2–TiO2 electrode exhibits a capacity of 497 mAh g−1 after 100 cycles at a charge rate of 2 C. Diffusion measurements indicate that no inhibition of lithium diffusion occurs due to a thin TiO2 coating. The superior capacity retention of the composite electrode may be attributed to the protection of SnO2 from irreversible reactions using a TiO2 coating.

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Ever increasing demand for efficient portable energy storage systems has directed researchers towards finding alternatives for the conventional insertion – based lithium-ion battery cathodes. Sulfur, with a theoretical specific capacity of 1672 mAh/g is a promising candidate for high energy density lithium battery cathodes1, 2. Low cost and ease of availability further adds to the advantages of sulfur over hitherto transition metal – based cathodes. However, elemental sulfur has very low electronic conductivity (~10-15 S/cm)3 at room temperature which restricts the active material utilization in Li – S battery. The formation of soluble non – intercalation based polysulfide intermediates (Li2Sn; n = 2 – 8)4 during electrochemical cycling further results in active material loss by coating onto the anode leading to eventual battery failure. Embedding sulfur into porous materials have shown considerable reduction in polysulfide dissolution by preventing direct contact with the liquid electrolyte5-7. However, inability to precisely control porosity and lack of chemical interaction between these porous structures and the entrapped sulfur greatly limits the efficiency of this approach. To completely prevent polysulfide dissolution, sulfur hosts with tunable, engineered porosity and increased affinity for polysulfide needs to be engineered. In this work, chemically coupled conductive complex framework materials (C4FMs) with nanoporous structure were used as hosts for sulfur in Li – S battery. Introduction of special functional groups improves the affinity of these structures towards polysulfide. The frameworks were synthesized using microwave assisted hydrothermal synthesis and then infiltrated with sulfur using vapor infiltration techniques. These sulfur – hosted cathodes showed a stable electrochemical performance with an initial discharge capacity of ~1620 mAh/g which stabilized at 1100 mAh/g to100 cycles (Figure 1). Acknowledgements: The authors acknowledge the financial support of DOE grant DE-EE 0006825, Edward R. Weidlein Chair Professorship funds and the Center for Complex Engineered Multifunctional Materials (CCEMM). References 1. J. R. Akridge, Y. V. Mikhaylik and N. White, Solid State Ionics, 2004, 175, 243-245. 2. M. M. Thackeray, C. Wolverton and E. D. Isaacs, Energy & Environmental Science, 2012, 5, 7854-7863. 3. M. Edeling, R. W. Schmutzler and F. Hensel, Philosophical Magazine Part B, 1979, 39, 547-550. 4. S. S. Zhang, Journal of Power Sources, 2013, 231, 153-162. 5. S.-R. Chen, Y.-P. Zhai, G.-L. Xu, Y.-X. Jiang, D.-Y. Zhao, J.-T. Li, L. Huang and S.-G. Sun, Electrochimica Acta, 2011, 56, 9549-9555. 6. Z. Gong, Q. Wu, F. Wang, X. Li, X. Fan, H. Yang and Z. Luo, RSC Advances, 2016, 6, 37443-37451. 7. J. Jin, Z. Wen, G. Ma, Y. Lu and K. Rui, Solid State Ionics, 2014, 262, 170-173. Figure 1

Lithium-ion batteries have been the dominant choice for batteries for decades, however there are concerns related to the limited availability of lithium, which could potentially increase the cost and affect further implementation. As a promising alternative, sodium-ion batteries have attracted significant attention in recent years [1, 2]. The potential markets for sodium-ion batteries could range from devices where cycle life and cost are more prevailing factors than energy density, such as grid-scale energy storage for smart grid applications. A single-step, facile spray pyrolysis is being evaluated in this group for the synthesis of sodium-ion battery cathode materials. In the current study, Na0.44MnO2 was selected due to its promising electrochemical performance, unique structure, and its similarity to transition metal oxides [3, 4]. Figure 1 shows the SEM image of Na0.44MnO2 annealed at 800 ºC. The material demonstrates a uniform, rod-like morphology. Figure 2 displays the XRD data of samples annealed at different temperatures for two hours. Na0.44MnO2 has an orthorhombic lattice cell (pbam space group) and is isostructural with Na4Mn4Ti5O18. The sample annealed at 700 ºC displays impurity peaks around the 30º 2θ. These impure phases may be related to the incomplete decomposition at this temperature. There are no additional phases observed in the 800 ºC and 900 ºC annealed samples. Figure 3 shows the first cycle voltage profile of the Na0.44MnO2 (annealed at 800 ºC) cell at C/10, where 1C equals to 120 mAg-1. The material demonstrates a discharge capacity of 100 mAhg-1, which is comparable to materials reported from other synthesis methods. References: 1.      M.D. Slater, D. Kim, E. Lee, C.S. Johnson, Advanced Functional Materials, Sodium-Ion Batteries, 23(8), 2013, 947-958. 2.     V. Palomares, P. Serras, I. Villaluenga, K.B. Hueso, J. Carretero-Gonzalez, T. Rojo, Energy and Environmental Science, Na-ion batteries, recent advances and present challenges to become low cost energy storage systems, 5(3), 2012, 5884-5901. 3.      F. Sauvage, L. Laffont, J.M. Tarascon, E. Baudrin, Inorganic Chemistry, Study of the insertion/deinsertion mechanism of sodium into Na0.44MnO2, 46(8), 2007, 3289-3294. 4.      L.W. Zhao, J.F. Ni, H.B. Wang, L.J. Gao, RSC Advances, Na0.44MnO2-CNT electrodes for non-aqueous sodium batteries, 3(18), 2013, 6650-6655 Figure 1

An aerosol-chemical vapor deposition technique (ACVD) was utilized in order to deposit highly oriented, one-dimensional nanostructured metal-oxide thin films. Film morphology was controlled using various system parameters in order to obtained the desired columnar morphology. Tin dioxide (SnO2) was chosen as an electrode material due to its high theoretical charge capacity (790 mA-h-g-1), and titanium dioxide (TiO2) was chosen for its remarkable stability and low volume change during charging. The columnar morphology is particularly well suited to SnO2 as the space between the columns allows for accommodation of the large volume expansion the material experiences during charging. Electrodes of SnO2 columnar nanostructures were first synthesized using ACVD by depositing the structures directly on to the current collector. Depositing directly onto the current collector eliminates the need for binding agents and conductive additives during battery fabrication. Then a layer of TiO2 was deposited on the surface of the SnO2 columns using atomic layer deposition. A variety of column heights, ranging from 500 nm to 2 um, and TiO2 layer thickness, ranging from no TiO2 to a 100 nm layer, were synthesized and their electrochemical properties investigated. For all electrochemical characterization experiments, Swagelok-type coin cells were fabricated using lithium foil as a counter electrode and 1M LiPF6 in 50/50 (v/v) EC/DEC as an electrolyte. Optimal electrochemical performance was observed in electrodes with a height of 800 nm and a 15 nm layer of TiO2. A rate capability test was performed to determine how the capacity of the electrodes changed at charging rates ranging from 100-2000 mA-g-1. A stable capacity of 410 mA-h-g-1 was obtained at a charge rate 1000 mA-g-1; rapid capacity fade was observed at higher rates. Galvanostatic charge-discharge was performed for each cell for 100 cycles or until failure at a charge rate of 400 mA-g-1, corresponding approximately to a charge rate of C/2. For the optimal electrode an initial irreversible capacity of 1164 mA-h-g-1 was observed as well as a stable capacity of 530 mA-h-g-1 after 100 cycles. This demonstrates a low cost synthesis of high performance anodes which provides an alternative to conventional electrode synthesis.