Well-defined double hysteresis loop in NaNbO3 antiferroelectrics.

Antiferroelectrics (AFEs) are promising candidates in energy-storage capacitors, electrocaloric solid-cooling, and displacement transducers. As an actively studied lead-free antiferroelectric (AFE) material, NaNbO3 has long suffered from its ferroelectric (FE)-like polarization-electric field (P-E) hysteresis loops with high remnant polarization and large hysteresis. Guided by theoretical calculations, a new strategy of reducing the oxygen octahedral tilting angle is proposed to stabilize the AFE P phase (Space group Pbma) of NaNbO3. To validate this, we judiciously introduced CaHfO3 with a low Goldschmidt tolerance factor and AgNbO3 with a low electronegativity difference into NaNbO3, the decreased cation displacements and [BO6] octahedral tilting angles were confirmed by Synchrotron X-ray powder diffraction and aberration-corrected scanning transmission electron microscopy. Of particular importance is that the 0.75NaNbO3-0.20AgNbO3-0.05CaHfO3 ceramic exhibits highly reversible phase transition between the AFE and FE states, showing well-defined double P-E loops and sprout-shaped strain-electric field curves with reduced hysteresis, low remnant polarization, high AFE-FE phase transition field, and zero negative strain. Our work provides a new strategy for designing NaNbO3-based AFE material with well-defined double P-E loops, which can also be extended to discover a variety of new lead-free AFEs.

Edge-Rich Quasi-Mesoporous Nitrogen-Doped Carbon Framework Derived from Palm Tree Bark Hair for Electrochemical Applications.

Biomass with abundant resources and low price is regarded as potential sources of functionalized carbon-based energy storage and conversion electrode materials. Rational construction and development of biomass-derived carbon equipped with proper morphology, structure, and composition prove the key to highly efficient utilization of advanced energy storage systems. Herein, we use palm tree bark hair as a biomass source and prepare edge/defect-rich quasi-mesoporous carbon (QMC) by a direct pyrolysis followed by NaOH etching strategy. Then, the edge-rich quasi-mesoporous nitrogen-doped carbon (QMNC) is successfully fabricated through the hydrothermal method by making use of edge/defect-rich QMC and urea as carbon precursor and nitrogen source, respectively. The microstructure and composition of the resultant carbon materials are all detected by a series of techniques. In the meantime, the influence of the etching process on the preparation and electrochemical performance of edge-rich QMNC is systematically explored. The relevant results manifest that the as-prepared edge/defect-rich QMC not only possesses edge-rich plane, much increased specific surface area (SSA), and special quasi-mesopores but also reverses good conductivity and gains sufficient defects for subsequent N doping. After introducing N atoms, the obtained edge-rich QMNC exhibits outstanding capacitive property and oxygen reduction reaction performance, which are mainly attributed to the co-effect of edge-rich plane, large SSA, suitable pore structures, and effective N doping (including high doping amount and optimized N configurations). Clearly, our work not only offers an excellent biomass-derived carbon-based electrode material but also opens a fresh avenue for the development of advanced biomass-derived carbon-based electrode materials.

Facile Synthesis of ZnS/N,S Co-doped Carbon Composite from Zinc Metal Complex for High-Performance Sodium-Ion Batteries.

ZnS coated on N,S co-doped carbon (ZnS/NSC) composite has been prepared utilizing zinc pyrithione (C10H8N2O2S2Zn) as raw material via calcination. Through activation using Na2CO3 salt, ZnS nanoparticles encapsulated in NSC (denoted as A-ZnS/NSC) with mixed-crystal structure has also been obtained, which reveals much larger specific surface area and more bridges between ZnS and NSC. Based on the existence of bridges (C-S-Zn and S-O-Zn bonds) and the modification of carbon from N,S co-doping, the A-ZnS/NSC composite as an anode for sodium-ion batteries (SIBs) displays significantly enhanced electrochemical performances with a high reversible specific capacity of 516.6 mA h g-1 (at 100 mA g-1), outstanding cycling stability (96.9% capacity retention after 100 cycles at 100 mA g-1), and high rate behavior (364.9 mA h g-1 even at 800 mA g-1).

Graphene-Embedded Co3O4 Rose-Spheres for Enhanced Performance in Lithium Ion Batteries.

Co3O4 has been widely studied as a promising candidate as an anode material for lithium ion batteries. However, the huge volume change and structural strain associated with the Li+ insertion and extraction process leads to the pulverization and deterioration of the electrode, resulting in a poor performance in lithium ion batteries. In this paper, Co3O4 rose-spheres obtained via hydrothermal technique are successfully embedded in graphene through an electrostatic self-assembly process. Graphene-embedded Co3O4 rose-spheres (G-Co3O4) show a high reversible capacity, a good cyclic performance, and an excellent rate capability, e.g., a stable capacity of 1110.8 mAh g-1 at 90 mA g-1 (0.1 C), and a reversible capacity of 462.3 mAh g-1 at 1800 mA g-1 (2 C), benefitted from the novel architecture of graphene-embedded Co3O4 rose-spheres. This work has demonstrated a feasible strategy to improve the performance of Co3O4 for lithium-ion battery application.