Shizhong Cui

Double Metal Ions Synergistic Effect in Hierarchical Multiple Sulfide Microflowers for Enhanced Supercapacitor Performance

In this paper, the design, synthesis, and measurement of a new and hierarchically structured series of NixCo1-xS1.097 electroactive materials are reported. The materials were synthesized through an ion-exchange process using hierarchically structured CoS1.097 as precursors, and a strategy utilizing the synergistic effect of double metal ions was developed. Two complementary metal ions were used to enhance the performance of electrode materials. The specific capacitance of the electroactive materials was continuously improved by increasing the nickel ion content, and the electric conductivity was also enhanced when the cobalt ion was varied. Experimental results showed that the nickel ion content in NixCo1-xS1.097 could be adjusted from x = 0 to 0.48. Specifically, when x = 0.48, the composite exhibited a remarkable maximum specific capacitance approximately 5 times higher than that of the CoS1.097 precursors at a current density of 0.5 A g(-1). Furthermore, the specific capacitance of Ni0.48Co0.52S1.097 electrodes that were modified with reduced graphene oxide could reach to 1152 and 971 F g(-1) at current densities of 0.5 and 20 A g(-1) and showed remarkably higher electrochemical performance than the unmodified electrodes because of their enhanced electrical conductivity. Thus, the strategy utilizing the synergistic effect of double metal ions is an alternative technique to fabricate high-performance electrode materials for supercapacitors and lithium ion batteries.

A nest-like Ni@Ni1.4Co1.6S2 electrode for flexible high-performance rolling supercapacitor device design

Herein we fabricated a series of flexible electrode materials with nickel foam as a partly self-sacrificial template by an in situ growth solvent thermal method. We synthesized a nest-like Ni@Ni3S2 electrode material with building blocks of ∼80 nm diameter nanowires. The growth mechanism of nest-like Ni@Ni3S2 electrode materials was studied through time-dependent experiments, in which the control of material morphology was realized. Residual metal nickel in the framework bestows the as-obtained electrode materials with excellent flexibility. The nest-like Ni@Ni1.4Co1.6S2 electrode material with a similar morphology and structure to Ni@Ni3S2 was fabricated using the Ni@Ni3S2 material as the template by a Co-exchange method. Continuous transition from Ni3S2 to Co9S8 was achieved depending on different replacement times. The synergistic and complementary advantageous effects of Co and Ni ions enhanced the specific capacitances from 89 F g−1 (Ni@Ni3S2) to 122 F g−1 (Ni@Ni1.4Co1.6S2) at a current density of 1 A g−1 at a high loading level of ∼20 mg cm−2. Moreover, the cycle stability and coulombic efficiency of the Ni@Ni3S2 electrode material were also increased by the introduction of Co ions. All the as-assembled Ni@Ni3S2 and Ni@Ni1.4Co1.6S2//activated carbon supercapacitor devices possessed high energy and power density, suggesting their potential application in high-performance flexible asymmetric rolling supercapacitor devices.

Synergistic effect induced ultrafine SnO2/graphene nanocomposite as an advanced lithium/sodium-ion batteries anode

SnO2/graphene materials have received extensive attention in broad applications owning to their excellent performances. However, multi-step and harsh synthetic methods with high temperatures and high pressures are major obstacles that need to be overcome. Herein a simple, low-cost, and scalable approach is proposed to construct ultrafine SnO2/graphene nanomaterials effectively under constant pressure and at the low temperature of 80 °C for 4 h, in which ultrafine SnO2 nanoparticles grow on graphene sheets uniformly and firmly via Sn–O–C bonding. This result depends on the synergetic effect of two reactions, the reduction of graphene oxide and formation of SnO2 nanoparticles, which are achieved successfully. More importantly, the constructed SnO2/graphene material exhibits excellent electrochemical properties in both lithium-ion batteries and sodium-ion batteries. As an anode material for lithium-ion batteries, it displays a high reversible capacity (1420 mA h g−1 at 0.1 A g−1 after 90 cycles) and good cycling life (97% at 1 A g−1 after 230 cycles), whereas in sodium-ion batteries, it maintains a capacity of 1280 mA h g−1 at 0.05 A g−1 and 650 mA h g−1 at 0.2 A g−1 after 90 cycles. The proposed synthetic methodology paves the way for the effective and large scale preparation of graphene-based composites for broad applications such as energy storage, optoelectronic devices, and catalysis.

Pyrite FeS2 microspheres anchoring on reduced graphene oxide aerogel as an enhanced electrode material for sodium-ion batteries

Pyrite, FeS2, is a promising sodium battery electrode candidate owing to its abundance in natural resources; however, it suffers from poor cyclic performance and poor rate performance, which hinders its large-scale commercial application. The semiconductor nature of pyrite as well as the dissolution of polysulfide and the destruction of the morphology of pyrite during the charge/discharge process are the main reasons for the abovementioned two drawbacks. In this study, a well-designed FeS2/rGO-A composite was constructed using an ambient temperature reaction. The introduction of rGO-A improved the conductivity of the entire material without hindering sodium ion diffusion; it also confined the pulverized active material to prevent its loss. Additionally, by controlling the cutoff voltage above 0.8 V, the formation of polysulfide was avoided. As a result, the FeS2/rGO-A electrode displays both excellent cyclic performance (low decay rate of 0.051% per cycle over 800 cycles at 1C) and rate performance (more than 70% discharge capacity is retained at 5C compared to 0.1C). The unique electrochemical mechanism was also investigated in detail. A new perspective of pyrite electrochemical behavior was obtained. This study provides not only a theoretical basis for further study, but may also enable the large-scale commercial application of sodium-ion batteries.

Controlled synthesis of 3D hierarchical NiSe microspheres for high-performance supercapacitor design

In this work, hierarchical nanosheet-based NiSe microspheres were successfully fabricated using a facile one-step solvothermal method, in which ethylenediamine and N,N-dimethylformamide were used as the mixed solvent. The evolution of this morphology and the effects of cetyltrimethylammonium bromide were also explored. The as-synthesized NiSe microspheres exhibited the ideal performance when employed as electrode materials of supercapacitors.

Hierarchical ternary Ni-Co-Se nanowires for high-performance supercapacitor device design.

Large-scale uniform Ni-Co-Se bimetallic ternary nanowires have been successfully synthesized through a successive cation exchange. First, NiSe nanowires in situ grown on nickel foam (NF) were prepared by a facile solvothermal route. Next, a series of ternary materials possessing different proportions of Ni and Co were fabricated by a Co-exchange method using the Ni@NiSe material as a template, which effectively achieved morphological inheritance from the parent material. To explore the electrochemical performance, all synthetic materials were assembled into asymmetric supercapacitor devices. Among asymmetric supercapacitor devices, the Ni@Ni0.8Co0.2Se//active carbon (AC) device exhibited a high specific capacitance of 86 F g-1 at a current density of 1 A g-1 and excellent cycling stability with virtually no decrease in capacitance after 2000 continuous charge-discharge cycles. This device still delivered an energy density of 17 Wh kg-1 even at a high power density of 1526.8 W kg-1. These superior electrochemical properties of Ni@Ni0.8Co0.2Se as an electrode material for supercapacitor devices confirmed the synergistic effect between Co and Ni ions, suggesting their potential application in the field of energy storage.

From α-NaMnO2 to crystal water containing Na-birnessite: enhanced cycling stability for sodium-ion batteries

In this work, α-NaMnO2 has been synthesized first. And then, after reacting with water, α-NaMnO2 translates into crystal water containing Na-birnessite with a large interlayer distance of 7.15 A. The synthesized α-NaMnO2 exhibits a discharge capacity (126.4 mA h g−1) higher than that of the crystal water containing Na-birnessite (100.9 mA h g−1). However, the crystal water containing Na-birnessite exhibits a cycling stability higher than α-NaMnO2 owing to the larger interlayer distance of Na-birnessite with the crystal water in the interlayer. Therefore, an effective way to improve the cycling stability of this kind of material is by changing the interlayer distance.

Construction of hierarchical three-dimensional interspersed flower-like nickel hydroxide for asymmetric supercapacitors

Low-cost and easily obtainable electrode materials are crucial for the application of supercapacitors. Nickel hydroxides have recently attracted intensive attention owning to their high theoretical specific capacitance, high redox activity, low cost, and eco-friendliness. In this study, novel three-dimensional (3D) interspersed flower-like nickel hydroxide was assembled under mild conditions. When ammonia was used as the precipitant and inhibitor and CTAB was used as an exfoliation agent, the obtained exfoliated ultrathin Ni(OH)2 nanosheets were assembled into 3D interspersed flower-like nickel hydroxide. In this novel 3D structure, the ultrathin Ni(OH)2 nanosheets not only provided a large contact area with the electrolyte, reducing the polarization of the electrochemical reaction and providing more active sites, but also reduced the concentration polarization in the electrode solution interface. Consequently, the utilization efficiency of the active material was improved, yielding a high capacitance. The electrochemical performance was improved via promoting the electrical conductivity by mixing the as-synthesized Ni(OH)2 with carbon tubes (N-4-CNT electrode), yielding excellent specific capacitances of 2,225.1 F·g–1 at 0.5 A·g–1 in a three-electrode system and 722.0 F·g–1 at 0.2 A·g–1 in a two-electrode system. The N-4-CNT//active carbon (AC) device exhibited long-term cycling performance (capacitance-retention ratio of 111.4% after 10,000 cycles at 5 A·g–1) and a high specific capacitance of 180.5 F·g–1 with a high energy density of 33.5 W·h·kg–1 and a power density of 2,251.6 W·kg–1.

A Highly Stretchable Nanofiber-Based Electronic Skin with Pressure-, Strain-, and Flexion-Sensitive Properties for Health and Motion Monitoring

The development of flexible and stretchable electronic skins that can mimic the complex characteristics of natural skin is of great value for applications in human motion detection, healthcare, speech recognition, and robotics. In this work, we propose an efficient and low-cost fabrication strategy to construct a highly sensitive and stretchable electronic skin that enables the detection of dynamic and static pressure, strain, and flexion based on an elastic graphene oxide (GO)-doped polyurethane (PU) nanofiber membrane with an ultrathin conductive poly(3,4-ethylenedioxythiophene) (PEDOT) coating layer. The three-dimensional porous elastic GO-doped PU@PEDOT composite nanofibrous substrate and the continuous self-assembled conductive pathway in the nanofiber-based electronic skin offer more contact sites, a larger deformation space, and a reversible capacity for pressure and strain sensing, which provide multimodal mechanical sensing capabilities with high sensitivity and a wide sensing range. The nanofiber-based electronic skin sensor demonstrates a high pressure sensitivity (up to 20.6 kPa-1), a broad sensing range (1 Pa to 20 kPa), excellent cycling stability and repeatability (over 10,000 cycles), and a high strain sensitivity over a wide range (up to approximately 550%). We confirmed the applicability of the nanofiber-based electronic skin to pulse monitoring, expression, voice recognition, and the full range of human motion, demonstrating its potential use in wearable human-health monitoring systems.

Hetero-nuclear coordinated compounds for use in high-performance supercapacitor electrode material design

Single crystals of cobalt coordination compounds were obtained by one-pot hydrothermal reaction. Nickel ion exchange was used to produce the Ni–Co hetero-metal compound with tunable chemical composition. Using a nickel-exchanged compound as the precursor, we developed a simple chemical reaction to synthesize large-scale 3D hierarchical NixCo3−xS4 (x = 0.15–0.42) microflowers under ambient conditions. As an electrode material for supercapacitors, the discharge capacitance of Ni0.42Co2.58S4 microflowers is approximately one and a half times higher than the discharge capacitance value of Ni0.15Co2.75S4 at a current density of 0.5 A g−1.