Search

Herein, a salt-assisted hydrothermal carbonization (HTC) strategy is applied to fabricate low-surface-area carbon microspheres (as low as 5.5 m2 g−1) for sodium ion batteries (SIBs) by using water containing eutectic salt melt (e.g. NaCl) and sugar (e.g. glucose) as reaction media. The small amount of salt increases the carbon conversion efficiency from 15.0 to 58.3%, and microsphere size from the nanoscale to the microscale. Meanwhile, the specific surface area of carbon microsphere is minimized and the microstructure is optimized. Ex-situ X-ray diffraction (XRD) and kinetic analysis revealed that the narrower lateral width of pseudographitic domains and lower micropore volume are the key factors to promote sodium storage ability and Na ion diffusion. The carbon microsphere anode delivers a capacity of 350 mAh g−1 with 73.0% from the low potential (0–0.2 V) at 100 mA g−1, a high initial Coulombic efficiency (ICE) of 86.1% (excluding conductive carbon black), and an excellent rate capability with capacity of 261 mAh g−1 even at 500 mA g−1. This research highlights a salt-assisted HTC method to synthesize low-surface-area carbon microspheres with superior ICE and energy/power density. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Developing high-performance anode materials is very crucial for room-temperature sodium-ion batteries (SIBs). Sn-based compounds are promising SIB anode materials for their high theoretical capacities and low costs. However, the intrinsic low conductivity, poor infiltration and irreversible reactions of Sn-based compounds lead to poor rate and cycling performance. In order to address above issues, SnS/SnS 2 heterostructures on sulfur-doped reduced graphene oxide (SG) are assembled via a facile alkali ion-assisted growth. As-synthesized SnS/SnS 2 heterostructures on SG with assistance of K+, denoted as SnS/SnS 2 @SG-K, exhibits typical layer-stacked structure and high reversible capacities over 800 mAh g−1 at 50 mA g−1 and 241 mAh g−1 even at a record high current density of 48 A g−1, which are superior to most of the Sn-based SIB anode materials. The excellent rate and cycling performance of SnS/SnS 2 @SG-K could be ascribed to the layer-stacked structures of SG and heterojunctions between SnS and SnS 2 which can accelerate semi-infinite diffusions of Na+ ions and electrons, alleviate polysulfide shuttling problems and reduce volume fluctuation effect. Meanwhile, the pseudocapacitance of oxygen and sulfur-containing groups in SG also contribute to the unprecedented sodium storage performance of as-synthesized SnS/SnS 2 @SG-K. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Carbon spheres (CS) with submicron size have demonstrated great potential in both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), in virtue of their tunable microstructure, facile dispersion in slurry, enabling densely packing along with enough interspace for effective electrolyte transportation. However, the synthesis of monodisperse CS with both uniform size and excellent energy storage performance at high charge/discharge rates is still very challenging. Herein, a surfactant-assisted hydrothermal growth strategy is proposed to produce monodisperse CS. Moreover, an ammonia treatment is adopted to boost up its capacity especially at high current densities. As-synthesized N-doped carbon spheres (NCS) exhibit excellent lithium/sodium ions storage ability which delivers reversible capacities of 580 mAh g−1 and 270 mAh g−1 for LIBs and SIBs respectively at a current density of 20 mA g−1. Moreover, NCS can retain 194 mAh g−1 at 4 A g−1 for LIBs and 90 mAh g−1 at 5 A g−1 for SIBs. The improving rate capacities of NCS can be attributed to the short diffusion lengths of Li+ and Na+ ions of uniform submicron structure, as well as large specific surface area (SSA), additional active sites and good conductivity provided by ammonia treatment. [ABSTRACT FROM AUTHOR]

Template method has been used as an important method to prepare porous materials. However, there are few reports about template method employing potassium chloride as template. Here, potassium chloride is employed as a template to prepare the porous carbon, and transition metal nitrates (Fe(NO 3 ) 2 ,d Co(NO 3 ) 2 , Ni(NO 3 ) 2 ) are introduced to catalyze graphitization and to result different carbon structure during carbonization (denoted as Fe@C, Co@C and Ni@C). The Fe@C shows a formicary-like structure with an about 20 nm pore diameter and the Co@C displays a completely compact structure. Whereas, the Ni@C exhibits a foam-like structure with hierarchical porous structure consisting of macroporous frameworks, mesopores and ultrathin porous walls (∼5 nm). Its macropore and mesopore diameter is around 100 nm and 4 nm, respectively, its specific surface area is 464.5 m 2  g −1 . When adopted as anode material, the Ni@C presents much outstanding rate and cycling capability for lithium and sodium storage than Fe@C and Co@C, the capacity for sodium storage is 260 mAh g −1 after 100 cycles at 100 mA g −1 and 92 mAh g −1 after 1000 cycles at 1A g −1 , and the capacity for lithium storage is 683 mAh g −1 after 1000 cycles at a current density of 1 A g −1 . [ABSTRACT FROM AUTHOR]

Sodium-ion capacitors (NICs) are considered an important candidate for large-scale energy storage in virtue of their superior energy–power properties, as well as availability of rich Na+ reserves. To fabricate high-performance NIC electrode material, a hydrothermal method was proposed to synthesize sulfur-doped reduced graphene oxide (SG), which exhibited unique layered structures and showed excellent electrochemical properties with 116 F/g capacitance at 1 A/g as the cathode of NICs from 1.6 V to 4.2 V. At the power–energy density over 5000 W/kg, the SG demonstrated over 100 Wh/kg energy density after 3500 cycles, which indicated its efficient durability and superior power–energy properties. The addition of a sulfur source in the hydrothermal process led to the higher specific surface area and more abundant micropores of SG when compared with those of reduced graphene oxide (rGO), thus SG exhibited much better electrochemical properties than those shown by rGO. Partially substituting surface oxygen-containing groups of rGO with sulfur-containing groups also facilitated the enhanced sodium-ion storage ability of SG by introducing sufficient pseudocapacitance. [ABSTRACT FROM AUTHOR]