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Cornlike ordered N-doped carbon coated hollow Fe3O4 (OH-Fe3O4@NC) composites are prepared through a facile strategy. The unique structure is composed of hundreds of N-doped carbon coated hollow Fe3O4 nanospheres. Successive carbon shell and hollow structure address the irreversibility issue of Fe3O4-based electrodes. Owing to the unique cornlike ordered structure, the as-prepared OH-Fe3O4@NC composites exhibit appealing electrochemical performance as anode materials for lithium-ion batteries (LIBs). It delivers a high reversible capacity of 1316 mA h g−1 at 0.1 A g−1 after 50 cycles and a remarkable rate performance (725, 551 and 361 mA h g−1 at 1, 4, and 10 A g−1, respectively). Our results demonstrate that the OH-Fe3O4@NC composites are the promising anode materials with high capacity for next generation LIBs.

Structures or materials with both high reflectivity in ultraviolet-visible-near infrared region (UV–Vis–NIR) and high emissivity in middle infrared region (MIR) can achieve radiative cooling. In this paper, a new crystal Mg11(HPO3)8(OH)6 was synthesized by hydrothermal method. Measurement results show that this crystal presents a reflectivity of 88.04% in 0.2–2.5 µm region and an emissivity of 87.57% in 2.5–25 µm region, suggesting that this material could reflect most of the solar light radiation, and in addition dissipate heat to the surroundings and outer space. The cell parameters and structure simulation diagram were obtained from the result of the Rietveld refinement. The properties and mechanisms were discussed based on X-ray diffraction, FTIR spectroscopy and electron microscopy results. The cooling test under strong sunshine showed that the temperatures in space below Mg11(HPO3)8(OH)6 coating were 2–4 °C lower than those below the coatings based on commercial solar heat reflection materials as TiO2 and CaCO3, and 6–8 °C lower than that below Al-foil, suggesting the potential application of the new crystal in radiative cooling.

Na-containing bilayer vanadium oxides offer outstanding storage capabilities for lithium and sodium batteries, but a multistep process for chemical pre-intercalation of Na-ion exposes a limitation for the application. Herein, we propose a facile one-pot hydrothermal approach to synthesize well crystallized bilayer NaxV2O5·nH2O with ketjen black as conductive dense-network. As a cathode in sodium-ion batteries, the resultant NaxV2O5·nH2O/ketjen black nanocomposite exhibits a high specific capacity of 239 mA h g-1 at a current density of 20 mA g−1 as well as an enhanced rate performance at high current rates up to 640 mA g−1. Ex situ XRD and XPS analysis are conducted to demonstrate the high specific capacity and investigate the changes in structure. Moreover, it is noticeable that two pronounced voltage plateaus reflect the high electrochemical activity of V4+/V5+, contributing to a remarkable energy density of 597 Wh kg−1, which is one of the highest records for cathode of sodium-ion batteries ever reported.

A new sodium ferrous orthophosphate Na x Fe4(PO4)3 (1.1 ≤ x ≤ 1.2) with P21/n symmetry has been successfully synthesized via a solid-state reaction for the first time. The structure consists of FeO5 pyramids, FeO6 octahedron, and PO4 tetrahedra which form large six-sided tunnels along $$ \vec{b} $$ direction and three- or four-sided tunnels running along $$ \vec{a} $$ direction. When evaluated as the anode materials for sodium-ion batteries, the first discharge and charge capacities of 553 and 264 mAh g−1 for Na1.1Fe4(PO4)3/C and 583 and 315 mAh g−1 for Na1.2Fe4(PO4)3/C, respectively, can be obtained at 10 mA g−1 current density. Compared to the Na1.1Fe4(PO4)3/C, Na1.2Fe4(PO4)3/C exhibits a better cycling performance, where the charge capacity of about 100 mAh g−1 can still be maintained after 15 cycles. The electrode kinetics are investigated further by the electrochemical impedance spectroscopy.

High-quality single crystalline gadolinium hexaboride (GdB6) nanowires have been successfully prepared at very low temperatures of 200–240 °C by a high pressure solid state (HPSS) method in an autoclave with a new chemical reaction route, where Gd, H3BO3, Mg and I2 were used as raw materials. The crystal structure, morphology, valence, magnetic and optical absorption properties were investigated using XRD, FESEM, HRTEM, XPS, SQUID magnetometry and optical measurements. HRTEM images and SAED patterns reveal that the GdB6 nanowires are single crystalline with a preferred growth direction along [001]. The XPS spectrum suggests that the valence of Gd ion in GdB6 is trivalent. The effective magnetic momentum per Gd3+ in GdB6 is about 6.26 μB. The optical properties exhibit weak absorption in the visible light range, but relatively strong absorbance in the NIR and UV range. Low work function and high NIR absorption can make GdB6 nanowires a potential solar radiation shielding material for solar cells or other NIR blocking applications.

A series of Fe-doped Na2Mn3-xFex(P2O7)2 (x = 0.0, 0.5, 1.0, 1.5 and 2.0) compounds have been successfully prepared by using sol-gel method. Rietveld refinement results indicate that single phase Na2Mn3-xFex(P2O7)2 with triclinic structure can be obtained within 0 ≤ x ≤ 2 although no Na2Fe3(P2O7)2 existing under our experimental conditions, and the cell parameters (including a, b, c and V) are decreasing with the increasing of x. Our results reveal that Na2Mn3(P2O7)2 exhibits an electrochemical activity in the voltage range of 1.5 V–4.5 V vs. Na+/Na when using as the cathode material for SIBs although it gives a limited rate capability and poor capacity retention. However, the electrochemical performance of Fe-doped Na2Mn3-xFex(P2O7)2 (0 ≤ x ≤ 2) can be improved significantly where cycle performance and rate capability can be improved significantly than that of the pristine one. Sodium ion diffusion coefficient can be increased by about two orders of magnitude with the Fe-doping content higher than x = 0.5.

A new alluaudite-type Na2VFe2(PO4)3 with carbon composite has been prepared for the first time via a simple sol-gel method using citric acid as an assistant agent and carbon source. The crystal structure and morphology of Na2VFe2(PO4)3/C composite are well characterized by X-ray diffraction, scan electron microscope, and energy-dispersive X-ray analysis. The experimental results show that a three-dimensional [VFe2(PO3)3]2− framework in this alluaudite structure provides two types of tunnels to enable the sodium-ion transporting which contributes to the electrochemical performance. When evaluated as a cathode for sodium-ion batteries, Na2VFe2(PO4)3/C composite delivers the first specific charge capacity of 66.7 mAh g−1 and discharge capacity of 65.8 mAh g−1 at 5 mA g−1 current density. After 100 cycles, the charge capacity (~52.2 mAh g−1at 5 mA g−1) shows a good capacity retention (~78%) compared to the first cycle. Cyclic voltammetric profiles confirm the activated multi-electron reactions including the Fe2+/Fe3+, V2+/V3+, and V3+/V4+ redox couples. Furthermore, the diffusion coefficient of sodium-ion (D Na +) in this structure is also calculated based on the result of electrochemical impedance spectroscopy.

A Co9S8/C nanocomposite is prepared using a solid-state reaction followed by a facile mechanical ball-milling treatment, with sucrose as the carbon source. The phases, morphologies, and detailed structures of the Co9S8/C nanocomposite are well-characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. When evaluated as an anode material for sodium-ion batteries, the Co9S8/C nanocomposite electrode displays a reversible capacity of ∼567 mA h g–1 in the initial cycle and maintains a reversible capacity of ∼320 mA h g–1 after 30 cycles, indicating a larger capacity and a stable cycling performance. For comparison, the electrochemical performances of Co9S8 and Co9S8/C samples synthesized using the solid-state reaction are also displayed. The ex situ XRD and transmission electron microscopy tests demonstrate that Co9S8 undergoes a conversion-type sodium storage mechanism.

Due to the limited resources of lithium source and their high price, lithium-ion batteries (LIBs) cannot meet the demands of future large-scale energy storage. Sodium-ion batteries (SIBs) with advantages of the abundant sodium resources and low cost, are one of the most promising alternatives to LIBs. Here, we firstly synthesize a new manganese-based polyanionic compound (Na3Mn2P3O11) through a simple sol-gel method. The resolved crystal structure indicates that single-phase Na3Mn2P3O11 compound belongs to the orthorhombic structure. When tested as for cathodes, it displays a poor electrochemical performance with a potential window of 1.8–4.3 V (versus Na/Na+), caused by the Jahn-Teller effect of Mn3+ generated during charging process. In this context, a series of Fe-doped Na3Mn2-xFexP3O11 (0.1 ≤ x ≤ 0.5) are prepared to improve the electrochemical performance. Results indicate that Fe substitution of Mn in Na2Mn2-xFexP3O11 structure can not only enhance the electrochemical performance, but also increase conductivity and achieve fast reaction kinetics. Noticeably, when iron-doped amount is 0.4, Na3Mn1.6Fe0.4P3O11 exhibits the best cycling (62.7 mA h g−1 at 0.1 C over 100 cycles) and rate performance (19.7 mA h g−1 at 5 C).