Sodium is globally available, which makes a sodium-ion rechargeable battery preferable to a lithium-ion battery for large-scale storage of electrical energy, provided a host cathode for Na can be found that provides the necessary capacity, voltage, and cycle life at the prescribed charge/discharge rate. Low-cost hexacyanometallates are promising cathodes because of their ease of synthesis and rigid open framework that enables fast Na(+) insertion and extraction. Here we report an intriguing effect of interstitial H2O on the structure and electrochemical properties of sodium manganese(II) hexacyanoferrates(II) with the nominal composition Na2MnFe(CN)6·zH2O (Na2-δMnHFC). The newly discovered dehydrated Na2-δMnHFC phase exhibits superior electrochemical performance compared to other reported Na-ion cathode materials; it delivers at 3.5 V a reversible capacity of 150 mAh g(-1) in a sodium half cell and 140 mAh g(-1) in a full cell with a hard-carbon anode. At a charge/discharge rate of 20 C, the half-cell capacity is 120 mAh g(-1), and at 0.7 C, the cell exhibits 75% capacity retention after 500 cycles.

The new Coronavirus SARS-CoV-2 has infected more than three million people worldwide so far. Brazil is currently the second leading country in number of critical cases and the third in number of new deaths caused by COVID-19, while São Paulo State accounts for more than 33% of total con rmed cases in Brazil. Therefore, understanding the mechanisms of SARS-CoV-2 spread in São Paulo State is an important task. The aim of this study was to assess environmental and social factors in uencing the spread of SARS-CoV-2 in the expanded metropolitan area of São Paulo, Brazil. Firstly, a spatial analysis was conducted to provide insights into the spread of COVID-19 within the expanded metropolitan area. Moreover, statistical analyses were performed to assess social indicators and environmental conditions which possibly in uence the incidence of COVID-19. Our results reveal that the spread of COVID-19 from the capital city São Paulo-its epicenter in Brazil-is directly associated with the availability of highways within the expanded metropolitan area of São Paulo. As for social aspects, cumulative COVID-19 con rmed cases were found to be both positively correlated with population density, and negatively correlated with social isolation rate, hence, indicating that social distancing has been effective in reducing the COVID-19 transmission. Finally, cumulative COVID-19 con rmed cases were found to be inversely correlated with both temperature and UV radiation. Together with recent literature our study suggests that the UV radiation provided by sunlight might reduce the infectivity of SARS-CoV-2.

A global priority is the development of low-cost, efficient storage of off-peak electric power and of electrical energy generated by energy sources other than fossil fuels (e.g. wind, solar, nuclear).[1] The rechargeable battery offers efficient electrical energy storage (EES), but the Li-ion battery used in hand-held devices is too expensive for large-scale EES. Unlike Li, Na is readily available worldwide and therefore much less costly than Li. However, the existing Na/S [2] and Zebra (Na/NiCl 2 ) [3] batteries are operating on molten electrodes at 250 to 350 8C. Therefore, there is a huge incentive to develop a room-temperature rechargeable, low-cost Na-ion battery (SIB) of high energy density capable of discharge/ charge at a high rate.To date, room-temperature rechargeable batteries have used as cathode oxide hosts into/from which the working ion, H + or Li + , can be inserted/extracted reversibly over a limited solid-solution range. These two working ions are able to be mobile guests in a host having a close-packed oxide-ion array. However, Na + is too large to be sufficiently mobile in a host with close-packed oxide ions; it needs a host framework with a larger interstitial space. Although Na + is stable coordinated by 12 oxide ions in an oxoperovskite, for example, the Na x WO 3 bronze, too high an activation energy is required for Na + transfer between these sites across a shared face coordinated by four oxide ions. The O-2p orbitals that s bond to the Na impede its motion. Replacement of the O 2À ions by (C N) À ions weakens bonding to the Na; the activation energy for Na + transfer is, therefore, strongly reduced, which makes attractive exploration of hexacyanoperovskites as cathode hosts for a rechargeable SIB. We report a synthesis route for a sodium manganese hexacyanoferrate (NMHFC) containing low-cost cations, and we demonstrate that the NMHFC provides a promising highrate performance as the cathode of a SIB of high specific energy density and efficient EES.Prussian blue and its analogues were investigated as hosts for alkali ions several years ago, [4] but that work received little attention. Cui and co-workers have recently reported stable Na + cyclability into potassium copper hexacyanoferrate in an aqueous electrolyte, [5] but an aqueous electrolyte limits the stable voltage of a rechargeable battery to 1.5 V. Therefore, we have chosen to investigate the hexacyano-perovskites in a non-aqueous electrolyte. We have reported the activities versus Na + /Na 0 of KMFe(CN) 6 with M = Fe, Co, Ni, Mn, Zn; high-spin M = Mn II showed a reversible plateau at 3.82 and 3.56 V, [6] respectively, on charge and discharge. We report herein removal of the Na + ion for a SIB to obtain a 3.4 V cathode in a Na half-cell with rhombohedral Na 1.72 MnFe(CN) 6 (NMHFC-1) and compare the performance with that of a cubic Na 1.40 MnFe(CN) 6 (NMHFC-2).The molar Na:Fe:Mn ratios of the sodium manganese hexacyanoferrates were obtained by inductively coupled plasma (ICP) analysis. All the metal atoms were normalized to the Mn c...