Lifang Jiao

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.

Tin Nanodots Encapsulated in Porous Nitrogen-Doped Carbon Nanofibers as a Free-Standing Anode for Advanced Sodium-Ion Batteries.

Ultrasmall Sn nanodots (1-2 nm) are homogeneously encapsulated in porous N-doped carbon nanofibers using a simple and scalable electrospinning method. The composite nanofibers weave into flexible free-standing membrane and can be directly used as binder- and current collector-free anode for Na-ion batteries, exhibiting excellent electrochemical performance with high reversible capacity, exceptional rate capability, and ultralong cycle life.

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.

A graphene-like MoS2/graphene nanocomposite as a highperformance anode for lithium ion batteries

In this article, we report on the preparation of a graphene-like MoS2/graphene nanocomposite by hydrolysis of lithiated MoS2 (LiMoS2) and its application as the anode material for lithium ion batteries. When the mass ratio of graphene/LiMoS2 is 15/100, the obtained composite (MoS2/GNS-15) displays a flower-like architecture composed of exfoliated nanosheets. The structure analyses further demonstrate that graphene-like MoS2 is supported on the surface of graphene nanosheets (GNS) and some of the interlayer spacings of MoS2 are enlarged with the intercalation of graphene. The reversible capacity of the MoS2/GNS-15 nanocomposite is ∼1400 mA h g−1 in the initial cycle and remains 1351 mA h g−1 after 200 cycles at 100 mA g−1. Furthermore, the capacity can reach 591 mA h g−1 even at a high current density of 1000 mA g−1. The excellent electrochemical performance of MoS2/GNS-15 is due to the synergetic effect between highly conductive GNS and graphene-like MoS2. On one hand, the GNS matrix can offer two-dimensional conductive networks and effectively suppress the aggregation of layered MoS2 during the lithiation/delithiation process. On the other hand, graphene-like MoS2 with an enlarged gallery can ensure the flooding of the electrolyte, provide more active sites and lower the diffusion energy barrier of Li+ ions.

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.

MnFe2O4@C Nanofibers as High-Performance Anode for Sodium-Ion Batteries

MnFe2O4 nanodots (∼3.3 nm) homogeneously dispersed in porous nitrogen-doped carbon nanofibers (denoted as MFO@C) were prepared by a feasible electrospinning technique. Meanwhile, MFO@C with the character of flexible free-standing membrane was directly used as binder- and current collector-free anode for sodium-ion batteries, exhibiting high electrochemical performance with high-rate capability (305 mA h g(-1) at 10000 mA g(-1) in comparison of 504 mA h g(-1) at 100 mA g(-1)) and ultralong cycling life (ca. 90% capacity retention after 4200 cycles). The Na-storage mechanism was systematically studied, revealing that MnFe2O4 is converted into metallic Mn and Fe after the first discharge (MnFe2O4 + 8Na(+) + 8e(-) → Mn + 2Fe + 4Na2O) and then to MnO and Fe2O3 during the following charge (Mn + 2Fe + 4Na2O → MnO + Fe2O3 + 8Na(+) + 8e(-)). The subsequent cycles occur through reversible redox reactions of MnO + Fe2O3 + 8Na(+) + 8e(-) ↔ Mn + 2Fe + 4Na2O, of which the reduction/oxidation of MnO/Mn takes place at a lower potential than that of Fe2O3/Fe. Furthermore, a soft package sodium-ion full battery with MFO@C anode and Na3V2(PO4)2F3/C cathode was assembled, delivering a stable capacity of ∼400 mA h g(-1) for MFO@C (with 100 cycles at 500 mA g(-1)) and a promising energy density of 77.8 Wh kg(-1) for the whole battery. This is owing to the distinctive structure of very-fine MnFe2O4 nanodots embedded in porous N-doped carbon nanofibers, which effectively improves the utilization rate of active materials, facilitates the transportation of electrons and Na(+) ions, and prevents the particle pulverization/agglomeration upon prolonged cycling.

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.