Zuolong Yu

Effects of functional groups of graphene oxide on the electrochemical performance of lithium-ion batteries

Graphene oxide (GO) with different ratios of functional groups are prepared via low temperature direct thermal reduction technology and re-oxidization by nitric acid, respectively. The structural, elemental, and oxygen-containing functional group compositions and electrochemical behaviors of the prepared GO are characterized using Fourier infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy, as well as charge/discharge curves and electrochemical impedance spectra measurements. Compared with graphite and graphene, the enhanced reversible capacity of GO is attributed to the oxygen-containing functional groups and the improved capacities are attributed predominantly to carbonyl and carboxyl groups. Besides, labile oxygen functionalities, such as epoxy groups, have a negative effect on the electrochemical properties, which lower the initial coulomb efficiency of graphene oxide anode materials. These findings may be beneficial to the material design of graphene-based anode materials with a high energy density.

Electrochemical Performance of Si/Graphite/Carbon Composite Electrode in Mixed Electrolytes Containing LiBOB and LiPF6

The influences of lithium bis(oxalato) borate (LiBOB), vinylene carbonate (VC)-containing LiPF 6 , and the mixed electrolytes with their different ratios on the electrochemical properties of Si/graphite/disordered carbon (Si/G/DC) composite electrode were investigated. Si/G/DC in mixed electrolytes presented better cyclability than in LiPF 6 with VC and a higher specific capacity than in LiBOB. Si/G/DC in 0.5 M LiBOB + 0.38 M LiPF 6 electrolytes exhibited a high reversible capacity of 512 mAh g -1 and a high and stable coulombic efficiency after the first cycle when cycled at a rate of 168 mA g -1 . Even after 220 cycles, the reversible capacity was still as high as 432 mAh g -1 , with a capacity fading of less than 0.08% per cycle. The analysis of scanning electron microscopy, electrochemical impedance spectra, and X-ray photoelectron spectroscopy indicated that the improvement of Si/G/DC composite electrode in cyclability resulted from the formation of impact and stable solid electrolyte interphase layers.

Improved rate capability of a LiNi1/3Co1/3Mn1/3O2/CNT/graphene hybrid material for Li-ion batteries

In this work, a LiNi1/3Co1/3Mn1/3O2/CNT/Graphene nanosheet (NCM/CNT/GN) hybrid material has been successfully prepared by a facile wet chemical method. The hierarchical structures of the CNT and GN are well maintained in the NCM/CNT/GN hybrid material, and their addition does not affect the layered crystal structure of the NCM. It is found that the NCM/CNT/GN hybrid material forms a three-dimensional (3D) spider-web like network structure via the interconnection of one-dimensional CNT and two-dimensional GN. As a result, the NCM/CNT/GN hybrid material exhibits the least electrode polarization, significantly enhanced rate capability with a high discharge capacity of 134 mA h g−1 at 3.0C, as well as excellent cycling performance. The improved electrochemical performances of NCM/CNT/GN hybrid material could be well correlated with the synergistic effects of CNT and GN, efficiently building the 3D conductive network, which largely enhances the electronic conductivity and the lithium ion diffusion in the NCM electrode.

Beam-size effect in time-delayed laser-induced double gratings

We have studied theoretically the effect of the probe-beam size on time-delayed laser-induced double gratings by assuming that the probe beam is described as a Gaussian beam. LettingEs1 andEs2 be the Four-Wave Mixing (FWM) signals originating from the diffraction of the probe beam by the gratings, the condition for the occurrence of the FWM signal modulation is that the divergence angle ofEs1 andEs2 is larger than half of the intersection angle between the propagation directions ofEs1 andEs2. We have also proposed methods to increase the modulation contrast.