Recent advances of metal telluride anodes for high-performance lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs), which is important electrochemical energy storage technologies with high energy density and environmental benignity.

Two-dimensional (2D) transition-metal dichalcogenide materials show potential for use in alkali metal ion batteries owing to their remarkable physical and chemical properties. Nevertheless, the electrochemical energy storage performance is still impaired by the tendency of aggregation, volume, and morphological change during the conversion reaction and poor intrinsic conductivity. Until now, ultrathin molybdenum disulfide nanosheets with a metallic-phase structure on the inner surface of mesoporous hollow carbon spheres (M-MoS2@HCS) have rarely been investigated as an anode for sodium-ion batteries. In this work, a novel M-MoS2@HCS anode was designed and synthesized by employing a template-assisted solvothermal reaction. Structural and chemical analyses indicate that the M-MoS2 nanosheets with a larger interlayer spacing compared to their semiconductor counterpart grow on the inner surface of HCS via covalent interactions. When used as the anode materials for Na+ storage, the M-MoS2@HCS anode presents durable and rapid sodium storage properties. The developed electrode shows a reversible capacity of 291.2 mAh g–1 at a high current density of 5 A g–1. After 100 cycles at 0.1 A g–1, the reversible capacity is 401.3 mAh g–1 with a capacity retention rate of 79%. After 2500 cycles at 1.0 A g–1, the electrode still delivers a reversible capacity of 320.1 mAh g–1 with a capacity retention rate of 75%. The excellent sodium storage capability of the MoS2@HCS electrode is explained by the special structural design, which reveals great potential to accelerate the practical applications of transition-metal dichalcogenide electrodes for sodium storage.

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Superfluorescence appears as an intense background in femtosecond time-resolved fluorescence noncollinear optical parametric amplification spectroscopy, which severely interferes the reliable acquisition of the time-resolved fluorescence spectra especially for an optically dilute sample. Superfluorescence originates from the optical amplification of the vacuum quantum noise, which would be inevitably concomitant with the amplified fluorescence photons during the optical parametric amplification process. Here, we report the development of a femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectrometer assisted with a 32-channel lock-in amplifier for efficient rejection of the superfluorescence background. With this spectrometer, the superfluorescence background signal can be significantly reduced to 1/300-1/100 when the seeding fluorescence is modulated. An integrated 32-bundle optical fiber is used as a linear array light receiver connected to 32 photodiodes in one-to-one mode, and the photodiodes are further coupled to a home-built 32-channel synchronous digital lock-in amplifier. As an implementation, time-resolved fluorescence spectra for rhodamine 6G dye in ethanol solution at an optically dilute concentration of 10(-5)M excited at 510 nm with an excitation intensity of 70 nJ/pulse have been successfully recorded, and the detection limit at a pump intensity of 60 μJ/pulse was determined as about 13 photons/pulse. Concentration dependent redshift starting at 30 ps after the excitation in time-resolved fluorescence spectra of this dye has also been observed, which can be attributed to the formation of the excimer at a higher concentration, while the blueshift in the earlier time within 10 ps is attributed to the solvation process.

Thanks to the low cost and earth's abundant potassium resources, potassium ion batteries (PIBs) have attracted much interest as alternative energy storage devices. However, there is still a great challenge...

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We report an improved setup of femtosecond time-resolved fluorescence non-collinear optical parametric amplification spectroscopy (FNOPAS) with a 210 fs temporal response. The system employs a Cassegrain objective to collect and focus fluorescence photons, which eliminates the interference from the coherent photons in the fluorescence amplification by temporal separation of the coherent photons and the fluorescence photons. The gain factor of the Cassegrain objective-assisted FNOPAS is characterized as 1.24 × 10(5) for Rhodamine 6G. Spectral corrections have been performed on the transient fluorescence spectra of Rhodamine 6G and Rhodamine 640 in ethanol by using an intrinsic calibration curve derived from the spectrum of superfluorescence, which is generated from the amplification of the vacuum quantum noise. The validity of spectral correction is illustrated by comparisons of spectral shape and peak wavelength between the corrected transient fluorescence spectra of these two dyes acquired by FNOPAS and their corresponding standard reference spectra collected by the commercial streak camera. The transient fluorescence spectra of the Rhodamine 6G were acquired in an optimized phase match condition, which gives a deviation in the peak wavelength between the retrieved spectrum and the reference spectrum of 1.0 nm, while those of Rhodamine 640 were collected in a non-optimized phase match condition, leading to a deviation in a range of 1.0-3.0 nm. Our results indicate that the improved FNOPAS can be a reliable tool in the measurement of transient fluorescence spectrum for its high temporal resolution and faithfully corrected spectrum.