Yingchang Yang

Porous NiCo2O4 spheres tuned through carbon quantum dots utilised as advanced materials for an asymmetric supercapacitor

Carbon quantum dots (CQDs) tuned porous NiCo2O4 sphere composites are prepared for the first time via a reflux synthesis route followed by a post annealing treatment. Benefiting from the advantages of the unique porous structure with a large specific surface area, high mesoporosity and superior electronic conductivity, the as-obtained CQDs/NiCo2O4 composite electrode exhibits high specific capacitance (856 F g−1 at 1 A g−1), excellent rate capability (83.9%, 72.5% and 60.8% capacity retention rate at 20, 50 and 100 A g−1, respectively) and exceptional cycling stability (98.75% of the initial capacity retention over 10000 cycles at 5 A g−1). Furthermore, the assembled AC//CQDs/NiCo2O4 asymmetric supercapacitor manifests a high energy density (27.8 W h kg−1) at a power density of 128 W kg−1 or a high power density (10.24 kW kg−1) at the reasonable energy density of 13.1 W h kg−1 and remarkable cycling stability (101.9% of the initial capacity retention over 5000 cycles at 3 A g−1). The results above suggest a great potential of the porous CQDs/NiCo2O4 composites in the development of high-performance electrochemical energy storage devices for practical applications.

Carbon dots supported upon N-doped TiO2 nanorods applied into sodium and lithium ion batteries

N-doped TiO2 nanorods decorated with carbon dots with enhanced electrical-conductivity and faster charge-transfer have been fabricated utilizing a simple hydrothermal reaction process involving TiO2 powders (P25) and NaOH in the presence of carbon dots followed by ion exchange and calcination treatments. Due to the merits of the carbon dots, doping and nanostructures, the as-designed N–TiO2/C-dots composite utilized as anode materials for lithium-ion batteries can sustain a capacity of 185 mA h g−1 with 91.6% retention even at a high rate of 10 C over 1000 cycles. It is interesting to note that the ratios of capacitive charge capacity during such high rates for the N–TiO2/C-dots composite electrodes are higher than those at low rates, which likely explains the observed excellent rate capabilities. In contrast to lithium-ion batteries, sodium-ion batteries have gained more interest in energy storage grids because of the greater abundance and lower cost of sodium-containing precursors. The as-obtained N–TiO2/C-dots composites reported here and utilized as anode materials for sodium-ion batteries exhibit excellent electrochemical performances, including substantial cycling stabilities (the capacity retention ratios after 300 cycles at 5 C is 93.6%) and remarkable rate capabilities (176 mA h g−1 at 5 C, 131 mA h g−1 at 20 C); such performances are the greatest ever reported to date over other structured TiO2 or TiO2 composite materials.

Sodium/Lithium storage behavior of antimony hollow nanospheres for rechargeable batteries.

Sodium-ion batteries (SIBs) have come up as an alternative to lithium-ion batteries (LIBs) for large-scale applications because of abundant Na storage in the earths crust. Antimony (Sb) hollow nanospheres (HNSs) obtained by galvanic replacement were first applied as anode materials for sodium-ion batteries and exhibited superior electrochemical performances with high reversible capacity of 622.2 mAh g(-1) at a current density of 50 mA g(-1) after 50 cycles, close to the theoretical capacity (660 mAh g(-1)); even at high current density of 1600 mA g(-1), the reversible capacities can also reach 315 mAh g(-1). The benefits of this unique structure can also be extended to LIBs, resulting in reversible capacity of 627.3 mAh g(-1) at a current density of 100 mAh g(-1) after 50 cycles, and at high current density of 1600 mA g(-1), the reversible capacity is 435.6 mAhg(-1). Thus, these benefits from the Sb HNSs are able to provide a robust architecture for SIBs and LIBs anodes.

One-Dimensional Rod-Like Sb2S3-Based Anode for High-Performance Sodium-Ion Batteries

Due to the high theoretical capacity of 946 mAh g(-1), Sb2S3 can be employed as promising electrode material for sodium-ion batteries (SIBs). Herein, the sodium storage behaviors of one-dimensional (1D) Sb2S3-based materials (Sb2S3 and Sb2S3@C rods) are successfully studied for the first time, displaying good cyclability and rate capability owing to their unique morphology and structure. Specifically, the Sb2S3@C rods electrode presents greatly enhanced electrochemical properties, resulting from the introduction of thin carbon layers which can effectively alleviate the strain caused by the large volume change and simultaneously improve the conductivity of electrode during cycling. At a current density of 100 mA g(-1), it delivers a high capacity of 699.1 mAh g(-1) after 100 cycles, which corresponds to 95.7% of the initial reversible capacity. Even at a high current density of 3200 mA g(-1), the capacity can still reach 429 mAh g(-1). This achievement may be a significant exploration for develpoing novel 1D Sb-based materials or metal sulfide SIBs anodes.

Anatase TiO2 nanocubes for fast and durable sodium ion battery anodes

With the aim of advancing anatase TiO2 anodes for sodium ion batteries, crystalline titania nanocubes were employed and they delivered a gradually increasing capacity during the initial cycles, termed as an activation process. The number of necessary discharge–charge loops for total activation is dependent on the galvanostatic current density (about 20 cycles at 0.2 C, or 90 cycles at 1 C). A percentage of Ti3+ was detected after the activation, indicating an amount of irreversibly trapped sodium ions in the lattice. After the activation process, an excellent rate capability and outstanding cycling stability were presented. The reversible capacity reached 174, 132, and 108 mA h g−1 at rates of 1 C, 5 C, and 10 C, respectively. The capacity was sustained with a loss of less than 10% after 1000 discharge–charge cycles at a rate of 2 C or 10 C. The superior battery performance achieved by the nanocubes is related to the encircled {100} facets that are more favorable for sodium ion attachment compared to the {001} and {101} facets, as supported by first-principles calculations. From this work we can see the feasibility of optimizing electrode materials via rational surface structure construction based on theoretical calculations.

First exploration of Na-ion migration pathways in the NASICON structure Na3V2(PO4)3

Ion occupation and migration pathways are investigated to explore the ion-migration mechanism of Na3V2(PO4)3 with the help of first principles calculations. Na3V2(PO4)3 with a NASICON framework generates high performances as a cathode material in sodium-ion batteries.

Sb porous hollow microspheres as advanced anode materials for sodium-ion batteries

Sb porous hollow microspheres (PHMSs) were prepared by a replacement reaction employing Zn microspheres (MSs) as templates. The obtained Sb PHMSs were first applied as anode materials for sodium-ion batteries (SIBs) and showed a high reversible capacity of 617 mA h g−1 at a current density of 100 mA g−1 after 100 cycles, exhibiting a high capacity retention of 97.2%. Even at a high current density of 3200 mA g−1, the reversible capacity can also reach 312.9 mA h g−1. The superior electrochemical performance of Sb PHMSs can be attributed to the unique structural characteristic of Sb with porous and hollow structure, which can accommodate the volume change and facilitate the Na+ diffusion during the sodiation and desodiation process.

Enhanced sodium storage behavior of carbon coated anatase TiO2 hollow spheres

Carbon coated anatase TiO2 hollow spheres (CCAnTHSs) are prepared through the carbon wrapping of etched amorphous TiO2 solid spheres (AmTSSs). The as-obtained CCAnTHS composite is applied as an anode material for sodium-ion batteries (SIBs) for the first time, delivering excellent cycle stability. At a high current density of 5C, a reversible capacity of 140.4 mA h g−1 remained after 500 cycles. Especially, at a 25C rate it could still reach 84.9 mA h g−1 after 80 cycles. Briefly, the sodium storage performance of CCAnTHSs are superior to these of the amorphous TiO2 solid spheres and bare anatase TiO2 hollow spheres, mainly benefitting from the advantages of a unique hollow structure with a large specific surface area and a carbon coating with high electronic conductivity.

Alternating Voltage Introduced NiCo Double Hydroxide Layered Nanoflakes for an Asymmetric Supercapacitor

An electrochemical alternating voltage approach of producing NiCo double hydroxide (NiCoDH) layered ultrathin nanoflakes with large specific surface area (355.8 m(2) g(-1)), remarkable specific capacitance and rate capability is presented. The obtained NiCoDH as anode for asymmetric supercapacitors shows excellent energy density of 17.5 Wh kg(-1) at high power density of 10.5 kW kg(-1) and cycling stability (91.2% after 10,000 cycles).

Carbon quantum dot coated Mn3O4 with enhanced performances for lithium-ion batteries

A C quantum dot coated Mn3O4 composite (Mn3O4/Cdots) has been obtained for the first time by a green alternating voltage electrochemical approach. It is interesting to note that the morphology of Mn3O4 particles in the composite can be induced to form an octahedral structure through the introduction of C quantum dots. In particular, the as-produced Mn3O4/Cdots composite utilized as an anode material for lithium ion batteries demonstrates excellent electrochemical performances, showing an enhanced reversible discharge capacity of 934 mA h g−1 after 50 cycles at a current density of 100 mA g−1 which is almost five times as much as that of pure Mn3O4.