Yijing Wang

Update on anode materials for Na-ion batteries

Na-ion batteries have emerged in recent years, due to their advantages of natural abundance, low cost and environmental friendliness. In this article, we review the up-to-date research progress on anode materials for Na-ion batteries from five respects: carbon-based materials, alloy-based materials, metal oxides and sulfides based on conversion reaction, titanium-based compounds with insertion mechanism, and organic composites. In particular, we not only summarize the Na-storage mechanism of these anodes, but also discuss the failure mechanism. The problems and challenges associated with these anodes are pointed out. Furthermore, on the basis of extensive reports and our experimental studies, feasible strategies are suggested for designing high performance anode materials. After further in-depth exploration and investigation, we believe that Na-ion batteries are promising alternative to lithium-ion batteries for low cost and large-scale energy storage systems in the near future.

Co3S4 hollow nanospheres grown on graphene as advanced electrode materials for supercapacitors

A novel nanocomposite of Co3S4 hollow nanospheres grown on reduced graphene oxide (rGO) has been synthesized by a facile two-step method and used as an advanced electrode material for supercapacitors. The intriguing formation and attachment mechanism of these Co3S4 hollow nanospheres on graphene are investigated. More importantly, it is found that the electrochemical performance of the as-prepared nanocomposite could be effectively improved by the chemical interaction between rGO and Co3S4. Specifically, it exhibits a high specific discharge capacitance of 675.9 F g−1 at 0.5 A g−1 and 521.7 F g−1 at 5 A g−1. These results suggest the great promise of fabricating graphene-supported hybrid materials for high-performance energy applications.

Facile synthesis route of porous MnCo2O4 and CoMn2O4 nanowires and their excellent electrochemical properties in supercapacitors

Two types of porous cobalt manganese oxide nanowires (MnCo2O4 and CoMn2O4) with different structures have been successfully synthesized by thermal decomposition of organometallic compounds for the first time. Nitrilotriacetic acid (NA) was used as a chelating agent to coordinate Co(II) and Mn(II) ions in various molar ratios, in a hydrothermal condition. The microstructure of as-synthesized cobalt manganese oxides, composed of numerous nanoparticles, completely retains the 1D network structure of the Co–Mn–NA coordination precursors without structure collapse. Electrochemical properties of the cobalt manganese oxide materials have been tested for supercapacitors at room temperature. Both the MnCo2O4 and CoMn2O4 electrodes display the outstanding capacitive behaviors and superior electrochemical properties. The CoMn2O4 nanowire shows excellent capacitance and desirable rate performance (2108 F g−1 at 1 A g−1 and 1191 F g−1 at 20 A g−1) compared to that of the MnCo2O4 nanowire (1342 F g−1 at 1 A g−1 and 988 F g−1 at 20 A g−1). Electrochemical impedance spectra (EIS) results also reconfirm that the CoMn2O4 nanowires display more facile electrolyte diffusion and higher capacitor response frequency than MnCo2O4 nanowires. This can be ascribed to the facile electrolyte/OH− ion penetration and better Faradaic utilization of the electroactive surface sites that generated by the smaller particle size and higher surface area.

Novel flower-like CoS hierarchitectures: one-pot synthesis and electrochemical properties

Novel 3D flower-like CoS hierarchitectures and CoS microspheres have been synthesized by a facile solvothermal method. A growth mechanism has been proposed for the nanostructures. Temperature and precursor concentration are the key factors influencing the nanostructures. Electrochemical measurements display high discharge capacity and excellent cycle stability.

Facile synthesis and superior supercapacitor performances of three-dimensional cobalt sulfide hierarchitectures

Formation of three-dimensional cobalt sulfide hierarchitectures through a mechanism similar to Ostwald ripening has been investigated. Electrochemical measurements reveal that the CoS1.097nanostructure exhibits superior supercapacitor performances with high specific capacitances (555 F g−1 at 5 mA cm−2 and 464 F g−1 at 100 mA cm−2) and excellent cycle life in 2 M KOH solution.

Novel three-dimensional NiCo2O4 hierarchitectures: solvothermal synthesis and electrochemical properties

Three-dimensional flower-like NiCo2O4 hierarchitectures have been successfully prepared on a large scale via a facile solvothermal method followed by an annealing process. The as-synthesized NiCo2O4 flower-like architectures have uniform diameters of about 500 nm assembled by numerous nanosheets radially grown from the center. The possible growth mechanism of the unique structures has been investigated. Both the poly(vinylpyrrolidone) (PVP) surfactant and the formation of metal glycolate play important roles in the formation of these novel three-dimensional flower-like hierarchitectures. With a large surface specific area of 212.6 m2 g−1, this novel NiCo2O4 material exhibited a superior specific capacitance of 1191.2 F g−1 and 755.2 F g−1 at current densities of 1 and 10 A g−1, respectively, which suggests that 63.4% of the capacitance is still retained when the charge–discharge rate is increased from 1 A g−1 to 10 A g−1. This superior electrochemical performance of NiCo2O4 as an electrode material for supercapacitors can be ascribed to the synergetic effect of the porous structure and the small diffusion lengths in the nanosheet building blocks. The simple, versatile and cost-effective route reported here may provide a general methodology for the high-yield synthesis of metal cobaltite nanostructures featuring improved properties and structures.

Polyol-mediated synthesis of mesoporous α-Ni(OH)2 with enhanced supercapacitance.

Flower-like α-Ni(OH)2 microspheres composed of nanowires are prepared by a solvothermal method using triethylene glycol and water as the mixed solvent. The formation of this unique structure is attributed to the synergetic effect of dissolution-recrystallization procedure, Ostwald ripening, and aggregative lateral attachment. Experimental results indicate that the dielectric constant, viscosity, and the chain lengths of the alcohols in the solvent may greatly affect the morphology and size of the as-obtained α-Ni(OH)2 samples. Because of the high Brunauer, Emmett, and Teller (BET) nitrogen sorption surface area of 318 m(2) g(-1) and large pore volume, this sample displays a maximum discharge specific capacity of 1788.9 F g(-1) at a discharge current density of 0.5 A g(-1). Besides, rate performance of this sample is also excellent, indicating that this sample is promising in electrochemical supercapacitors.

Ultrasmall TiO2 Nanoparticles in Situ Growth on Graphene Hybrid as Superior Anode Material for Sodium/Lithium Ion Batteries.

To inhibit the aggregation of TiO2 nanoparticles and to improve the electrochemical kinetics of TiO2 electrode, a hybrid material of ultrasmall TiO2 nanoparticles in situ grown on rGO nanosheets was obtained by ultraphonic and reflux methods. The size of the TiO2 particles was controlled about 10 nm, and these particles were evenly distributed across the rGO nanosheets. When used for the anode of a sodium ion battery, the electrochemical performance of this hybrid TiO2@rGO was much improved. A capacity of 186.6 mAh g(-1) was obtained after 100 cycles at 0.1 A g(-1), and 112.2 mAh g(-1) could be maintained at 1.0 A g(-1), showing a high capacity and good rate capability. On the basis of the analysis of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), the achieved excellent electrochemical performance was mainly attributed to the synergetic effect of well-dispersed ultrasmall TiO2 nanoparticles and conductive graphene network and the improved electrochemical kinetics. The superior electrochemical performance of this hybrid material on lithium storage further confirmed the positive effect of rGO.

Facile synthesis and superior supercapacitor performances of Ni2P/rGO nanoparticles

Ni2P nanoparticles grown on reduced graphene oxide (rGO) were successfully synthesized via the low-temperature solid state reaction method and investigated as electrochemical pseudocapacitor materials for potential energy storage applications. The specific capacitance of the as-prepared Ni2P/rGO is 2266 F g−1 and the Ni2P/rGO composite also exhibits superior cycling performance when they are used as the capacitor materials. The as-prepared Ni2P/rGO sample demonstrates interesting supercapacitive properties with high capacitance and good cycling performance.

Facile carbonaceous microsphere templated synthesis of Co3O4 hollow spheres and their electrochemical performance in supercapacitors

Co3O4 hollow spheres assembled from nanoparticles have been successfully synthesized by a one-pot hydrothermal carbonization and calcination method. In this method, carbon spheres obtained through hydrothermal carbonization at a low temperature of 140 °C are used as sacrificial templates. The carbonization process was monitored by Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. Both the carbon sphere soft templates and the NH3 released from hexamethylenetetramine play key roles in the formation of these novel hollow structures. The formation of the Co3O4 hollow spheres using hydrothermal carbon spheres as templates can be attributed to the synergetic effect of metal ion adsorption and heterogeneous nucleation of Co(OH)2, which is different from the traditional adsorption theory. The as-obtained Co3O4 hollow microspheres exhibit excellent cycling performance and good rate capacity when used as electrode materials in supercapacitors, which can be attributed to the small particle size of Co3O4 and the sufficient space available to interact with the electrolytes. This facile strategy may be extended to synthesize other metal oxide hollow spheres, which may find application in sensors and catalysts due to their unique structural features.Graphical abstract