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10 results on '"Weng, Z. X."'

4. Preformed Boehmite Nanoparticles As Coating Materials for Long-Cycling LiCoO2.

Author

Fey, G. T. K., Weng, Z. X., Chen, J. G., Lu, C. Z., Kumar, T. P., Naik, S. P., Chiang, A.S.T., Lee, D.C., and Lin, J. R.

Subjects
*HYDROXIDE minerals, *BOEHMITE, *CATHODES, *NANOPARTICLES, *BAUXITE, *VOLTAMMETRY
Abstract

A simple mechano-thermal coating procedure for the production of long-cycling LiCoO2 is described. Preformed nanoparticulate boehmite was used as the coating material. The coating procedure resulted in the cathode particles covered in a 20-30 nm thick kernel of boehmite, as revealed by TEM examination. XRD studies showed that the lattice parameter c diminished upon coating, indicating that a substitutional compound of the composition LixAlyCo1-yO2 may have formed upon calcination. SEM images, R-factor values from XRD studies and galvanostatic charge-discharge studies showed that a coating level of 1.0 wt % gave an optimal performance in capacity and cyclability. SEM images showed that above the 1.0 wt % coating level, the excess boehmite adhered to the coated cathode particles as sperules. ESCA depth profile analysis showed partial diffusion of aluminum from the surface to the interior. Galvanostatic cycling studies showed that at a coating level of 1.0 wt %, cyclability improved three- and twelve-fold for the two commercial LiCoO2 samples tested. Cyclic voltammetry revealed that the hexagonal-monoclinic-hexagonal phase transformations during cycling were suppressed in the coated cathode materials. [ABSTRACT FROM AUTHOR]

Published
2004
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5. Preformed Boehmite Nanoparticles As Coating Materials for Long-Cycling LiCoO2.

Author

Fey, G. T. K., Weng, Z. X., Chen, J. G., Lu, C. Z., Kumar, T. P., Naik, S. P., Chiang, A.S.T., Lee, D.C., and Lin, J. R.

Subjects
HYDROXIDE minerals, BOEHMITE, CATHODES, NANOPARTICLES, BAUXITE, VOLTAMMETRY
Abstract

A simple mechano-thermal coating procedure for the production of long-cycling LiCoO2 is described. Preformed nanoparticulate boehmite was used as the coating material. The coating procedure resulted in the cathode particles covered in a 20-30 nm thick kernel of boehmite, as revealed by TEM examination. XRD studies showed that the lattice parameter c diminished upon coating, indicating that a substitutional compound of the composition LixAlyCo1-yO2 may have formed upon calcination. SEM images, R-factor values from XRD studies and galvanostatic charge-discharge studies showed that a coating level of 1.0 wt % gave an optimal performance in capacity and cyclability. SEM images showed that above the 1.0 wt % coating level, the excess boehmite adhered to the coated cathode particles as sperules. ESCA depth profile analysis showed partial diffusion of aluminum from the surface to the interior. Galvanostatic cycling studies showed that at a coating level of 1.0 wt %, cyclability improved three- and twelve-fold for the two commercial LiCoO2 samples tested. Cyclic voltammetry revealed that the hexagonal-monoclinic-hexagonal phase transformations during cycling were suppressed in the coated cathode materials. [ABSTRACT FROM AUTHOR]

Published
2004
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9. A New Model of Mechanism and Treatment of Kinetics for Styrene/N-Phenylmaleimide Copolymerization

Author

Shan, G.-R., Weng, Z.-X., Huang, Z.-M., and Pan, Z.-R.

Abstract

The copolymerization of styrene (St, M1) and N-phenylmaleimide (PMI, M2) in chloroform using 2,2‘-azobis(isobutyronitrile) as an initiator was investigated. A new kinetic model with assumption of homopolymerization and cross-propagation and diffusion-controlled termination was proposed. The reactivity ratios of free monomers and the charge-transfer complex (CTC) in the copolymerization were determined by a new method, and the values were obtained to be r12 = 0.03370, r21 = 0.01157, r1C = 0.002972, and r2C = 0.003379, respectively. A kinetic treatment based on the model of mechanism was used to quantitatively estimate the ratio of the CTC rate to the total copolymerization rate in the St/PMI copolymerization. It was about 33.0−55.0% in a wide range of monomer feed.

Published
1997

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