Hybrid supercapacitors are considered the next-generation energy storage equipment due to their superior performance. In hybrid supercapacitors, battery electrodes need to have large absolute capacities while displaying high cycling stability. However, enhancing areal capacity via decreasing the size of electrode materials results in reductions in cycling stability. To balance the capacity–stability trade-off, rationally designed proper electrode structures are in urgent need and still of great challenge. Here we report a high-capacity and high cycling stability electrode material by developing a nickel phosphate lamination structure with ultrathin nanosheets as building blocks. The nickel phosphate lamination electrode material exhibits a large specific capacity of 473.9 C g–1 (131.6 mAh g–1, 1053 F g–1) at 2.0 A g–1 and only about 21% capacity loss at 15 A g–1 (375 C g–1, 104.2 mAh g–1, 833.3 F g–1) in 6.0 M KOH. Furthermore, hybrid supercapacitors are constructed with nickel phosphate lamination and activated carbon (AC), possessing high energy density (42.1 Wh kg–1 at 160 W kg–1) as well as long cycle life (almost 100% capacity retention after 1000 cycles and 94% retention after 8000 cycles). The electrochemical performance of the nickel phosphate lamination structure not only is commensurate with the nanostructure or ultrathin materials carefully designed in supercapacitors but also has a longer cycling lifespan than them. The encouraging results show the great potential of this material for energy storage device applications.

A series of promising cyan, green, and yellow emission (Ba, Sr) 3 (Si, Al) 6 (O, N) 15 :Eu 2+ phosphors were synthesized by a Pechini-type sol−gel ammonolysis method. Variations in luminescence properties and crystal structure caused by the modification of phosphor composition were studied in detail. The prefired temperatures of the precursors play a key role in the process of forming the final products. Under UV light excitation, the as-prepared Ba 3 Si 6 O 15 :Eu 2+ phosphor presents a strong cyan emission located at 498 nm. Moreover, the as-prepared oxynitride phosphors, Eu 2+activated (Ba 1−y Sr y ) 3 Si 6−x Al x O 15−μ N δ (x = 0−1.2, y = 0−0.6), display a broader excitation band covering the entire visible region. Under blue light excitation, Ba 3 Si 6−x Al x O 15−μ N δ :Eu 2+ phosphors show a intense and narrow green emission at 520 nm, and the luminescent intensity can be enhanced by increasing Al content within a certain range. However, (Ba 1−y Sr y ) 3 Si 6 O 15−μ N δ :Eu 2+ phosphors exhibit green (520 nm) to yellow (554 nm) emission with increasing Sr content. Unexpectedly, Eu 2+ doped Ba 3 Si 6 O 9 N 4 -type Ba 3 Si 6 O 15−μ N δ −1300 °C phosphor exhibits a bluish green emission and strong thermal quenching behavior. The (Ba 1−y Sr y ) 3 Si 6−x Al x O 15−μ N δ :Eu 2+ phosphors exhibit a small thermal quenching, and the quantum yields measured under 460 nm excitation could reach up to 89% for green Ba 3 Si 6−x Al x O 15−μ N δ :Eu 2+ phosphor and 71% for yellow (Ba 1−y Sr y ) 3 Si 6x O 15−μ N δ :Eu 2+ phosphor. White LEDs with tunable color temperature and higher color rendering index were fabricated by combining the prepared cyan Ba 3 Si 6 O 15 :Eu 2+ /green Ba 2.91 Eu 0.09 Si 6−x Al x O 15−μ N δ (x = 0.06)/yellow (Ba 0.97−y Sr y ) 3 Eu 0.09 Si 6 O 15−μ N δ (y = 0.4) phosphor and a red phosphor with a UV or blue LED chip, indicating that they are promising phosphors for white LEDs.

In this work, we comparatively explored the electronic structure and the low-dimensional magnetic interactions of double-perovskite compounds SrCuTeO and SrCuWO through first-principles calculations. The electronic structure calculations indicate that the Cu (3d ) site is the only magnetic active one, whereas Te and W remain in nonmagnetic states with d and d electronic configurations, respectively. The magnetic exchange interactions have been evaluated on the basis of the classical Heisenberg model. Both SrCuTeO and SrCuWO should be strong frustrated 2D magnetism, in excellent agreement with the experimental observations. Nevertheless, the nearest-neighbor antiferromagnetic interaction J plays a determined role in constructing the Néel antiferromagnetic ordering within the square Cu framework of SrCuTeO. While, the next-nearest-neighbor antiferromagnetic interaction J transcends the nearest-neighbor interaction J, establishes the collinear antiferromagnetic ordering in SrCuWO. The discrimination has been explored and analyzed in detail using density of states, charge density as well as spin density analysis.

No abstract

Manganese oxides composed of various valence states Mn x+ (x = 2, 3, and 4) have attracted wide attention as promising electrode materials for asymmetric supercapacitor. However, the poor electrical conductivity limited their performance and application. Appropriate regulation content of Mn x+ in mixed-valent manganese oxide can tune the electronic structure and further improve their conductivity and performance. Herein, we prepared manganese oxides with different Mn2+/Mn3+ ratios through an over-reduction (OR) strategy for tuning the internal electron structure of mixed-valent manganese, which could make these material oxides a good platform for researching the structure–property relationships. The Mn2+/Mn3+ ratio of manganese oxide could be precisely tuned from 0.6 to 1.7 by controlling the amount of reducing agent for manipulating the redox processes, where the manganese oxide electrode with the most appropriate Mn2+/Mn3+ ratio, as 1.65 (OR4) exhibits large capacitance (274 F g–1) and the assembling asymmetric supercapacitors by combining OR4 (positive) and the commercial activated carbon (as negative) achieved large 2.0 V voltage window and high energy density of 27.7 Wh kg–1 (power density of 500 W kg–1). The cycle lifespan of the OR4//AC could keep about 92.9% after 10 000-cycle tests owing to the Jahn–Teller distortion of the Mn­(III)­O6 octahedron, which is more competitive compared to other work. Moreover, a red-light-emitting diode (LED) can easily be lit for 15 min by two all-solid supercapacitor devices in a series.