Prussian blue and its analogues consisting of different transitionmetal ions (Fe, Mn, Ni, Cu, Co and Zn) have been synthesized at room temperature. Insertion of Na into KFe 2 (CN) 6 in a carbonate electrolyte exhibited a reversible capacity near 100 mA h g À1 with no capacity fade in 30 cycles. The data indicate that a Na-ion battery with a Prussian blue framework as a cathode will be feasible.

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...

The coexistence and competition between superconductivity and electronic orders, such as spin or charge density waves, have been a central issue in high transition-temperature (Tc) superconductors. Unlike other iron-based superconductors, FeSe exhibits nematic ordering without magnetism whose relationship with its superconductivity remains unclear. Moreover, a pressure-induced fourfold increase of Tc has been reported, which poses a profound mystery. Here we report high-pressure magnetotransport measurements in FeSe up to ∼15 GPa, which uncover the dome shape of magnetic phase superseding the nematic order. Above ∼6 GPa the sudden enhancement of superconductivity (Tc≤38.3 K) accompanies a suppression of magnetic order, demonstrating their competing nature with very similar energy scales. Above the magnetic dome, we find anomalous transport properties suggesting a possible pseudogap formation, whereas linear-in-temperature resistivity is observed in the normal states of the high-Tc phase above 6 GPa. The obtained phase diagram highlights unique features of FeSe among iron-based superconductors, but bears some resemblance to that of high-Tc cuprates.