Xiayin Yao

Thin MoS2 Nanoflakes Encapsulated in Carbon Nanofibers as High-Performance Anodes for Lithium-Ion Batteries

In this work, highly flexible MoS2-based lithium-ion battery anodes composed of disordered thin MoS2 nanoflakes encapsulated in amorphous carbon nanofibrous mats were fabricated for the first time through hydrothermal synthesis of graphene-like MoS2, followed by electrospinning and carbonization. X-ray diffraction as well as scanning and transmission electron microscopic studies show that the as-synthesized MoS2 nanoflakes have a thickness of about 5 nm with an expanded interlayer spacing, and their structure and morphology are well-retained after the electrospinning and carbonization. At relatively low MoS2 contents, the nanoflakes are dispersed and well-embedded in the carbon nanofibers. Consequently, excellent electrochemical performance, including good cyclability and high rate capacity, was achieved with the hybrid nanofibrous mat at the MoS2 content of 47%, which may be attributed to the fine thickness and multilayered structure of the MoS2 sheets with an expanded interlayer spacing, the good charge conduction provided by the high-aspect-ratio carbon nanofibers, and the robustness of the nanofibrous mat.

Polydopamine-assisted synthesis of hollow NiCo2O4 nanospheres as high-performance lithium ion battery anodes

Hollow NiCo2O4 nanospheres with the outer diameter of about 60 nm and inner diameter of around 40 nm are prepared using monodisperse polydopamine spheres as the templates followed by a calcination process. The shell of the obtained NiCo2O4 is composed of nanoparticles with inter-particle spaces of below 10 nm. When they are employed as an anode in lithium-ion batteries, the hollow NiCo2O4 nanospheres with mesoporous shells exhibit superior electrochemical performances in terms of high reversible capacity, excellent rate capability and cycling stability. When galvanostatic discharging/charging at 0.2, 0.6, 1.0 and 2.0 A g−1, the anode can deliver discharge capacities as high as 1210, 1053, 923 and 659 mA h g−1, respectively. Moreover, the reversible capacity could be maintained at 695 mA h g−1 under the current density of 2.0 A g−1 for 200 cycles. These make the hollow NiCo2O4 nanospheres promising candidates for anode materials in high-energy and high-power lithium ion batteries.

Facile synthesis of porous CoFe2O4 nanosheets for lithium-ion battery anodes with enhanced rate capability and cycling stability

Porous CoFe2O4 nanosheets, having the thickness of 30–60 nm and lateral size of several microns with numerous penetrating pores, are synthesized via thermal decomposition of (CoFe2)1/3C2O4·2H2O nanosheets, which are facilely prepared through a poly(vinyl alcohol)-assisted precipitation-cum-self-assembly process in an aqueous medium. The obtained porous CoFe2O4 nanosheets are employed as anodes in lithium-ion batteries (LIBs). The anode exhibits excellent rate capability and cycling stability. When discharging–charging at 1 A g−1 and 2 A g−1, it can deliver discharge capacities as high as 806 mA h g−1 and 648 mA h g−1, respectively, each for 200 cycles. This makes the porous CoFe2O4 nanosheets promising candidates for anode materials in high-energy and high-power LIBs.

Polydopamine-derived porous nanofibers as host of ZnFe2O4 nanoneedles: towards high-performance anodes for lithium-ion batteries

In this work, highly mesoporous carbon nanofibers in free-standing mat form are successfully fabricated by single-spinneret electrospinning of polystyrene (PS) followed by coating the porous PS nanofibers via in situ polymerization of dopamine and subsequent annealing. The pores inside the nanofibers are mainly in the range of 10–50 nm and interconnected to each other, forming nanochannels. ZnFe2O4 crystals can then be grown from the nanofibers via a solution route. Strikingly, ZnFe2O4 nanoneedles are formed, which have diameter and length of about 8 nm and 70 nm, respectively, and are located evenly not only on the surface of the nanofibers but also inside the nanochannels. The ZnFe2O4/carbon composite nanofibers exhibit excellent cyclability and rate performance as anodes of lithium ion batteries (LIBs), in which the ZnFe2O4 nanoneedles are the major active component with normalized capacity of 1000–1700 mA h g−1 at 0.1 A g−1 and 560 mA h g−1 at 5 A g−1, respectively. The excellent properties can be ascribed to the very small diameter of the nanoneedles that ensures complete conversion reactions and alloying/de-alloying between Zn and lithium, the good contact of the nanoneedles with polydopamine-derived N-doped graphitic carbon that offer efficient electrical conduction, and the nanochannels that allow facile transport of the electrolyte and lithium ions.

Poly(vinylidene fluoride) nanofibrous mats with covalently attached SiO2 nanoparticles as an ionic liquid host: enhanced ion transport for electrochromic devices and lithium-ion batteries

In this article, it is demonstrated that the electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF–HFP)) nanofibrous mat functionalized with (3-aminopropyl)triethoxysilane is a versatile platform for the fabrication of hybrid nanofibrous mats by covalently attaching various types of inorganic oxide nanoparticles on the nanofiber surface via a sol–gel process. In particular, SiO2-on-P(VDF–HFP) nanofibrous mats synthesized using this method is an excellent ionic liquid (IL) host for electrolyte applications. The IL-based electrolytes in the form of free-standing mats are obtained by immersing SiO2-on-P(VDF–HFP) mats in two types of liquid electrolytes, namely LiClO4/1-butyl-3-methylimidazolium tetrafluoroborate and bis(trifluoromethane)sulfonimide lithium salt/1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide. It is found that the surface attached SiO2 nanoparticles can effectively serve as salt dissociation promoters by interacting with the anions of both ILs and lithium salts through Lewis acid–base interactions. They dramatically enhance the ionic conductivity and lithium transference number of the electrolytes. In addition, better compatibility of the electrolytes with lithium electrodes is also observed in the presence of surface-attached SiO2. Using IL-loaded SiO2-on-P(VDF–HFP) nanofibrous mats as the electrolytes, electrochromic devices display higher transmittance contrast, while Li/LiCoO2 batteries show significantly improved C-rate performance and cycling stability. This class of novel non-volatile electrolytes with high ionic conductivity also has the potential to be used in other electrochemical devices.