experimental
commercial Li with a 1.5% carbon content and about 2-4 m average particle diameter were purchased from alees company (Taiwan. China) and used as the raw meterial. For the fabrication of the nano-Li/c particles, 85% (weight percent) of the commercial Li powder and 15% glucose were ultrafinely milled using 0.5 mm zirconia balls and ethanol as a dispersant. After the ball milling for 1.5 h, the resultant slurry was sprayed and dried to get the nano-li/c precursor. Then the precursor was annealed at 600 C under Ar/H2 (5% vol. H) gas flow for 6 h to obtain the spherical materials. Under these conditions, 1 g of glucose yield about 0.24 g carbon, and the content of carbon in the material was about 5.0%-6.0%.
For the nano-Li hybrid preparation, the raw Li and 3% glucose were firstly untrafine ball milled for 1.5 h, and then 3% graphitized CNTs (Chengdu Organic Chemicals Co. Lid., Chinese Academy of Sciences) were added into the slurry. Then the mixed slurry was milled for another 2 h at 300 r/min to uniformly disperse the CNTs. Finally, the slurry was spray dried and sintered at 600 C in Ar/H for 6 h to yield the resultant nano-Li/c/cnt hybrid, the overall carbon content of this hybrid materialis also about 5.0%-6.0%
the morphology and struture of the samples were characterized by scanning electron microscopy (SEM.) transmission electron microscopy and XRD. The residual carbon content of the resultant Li Hybrid materails was determined by carbon sulfur analyzer
electrchemical experiments were performed using CR2032-type coin cell. For preparing working electrodes, a dispersant of the as-synthesized hybrid materials, carbon black, and poly(vinyl difluoride) (PVDF) at a weight ratio of pure AL foil. Typical loadings for the 50 m-thick coatings were 5 mg*cm-2 of cathode powder. Microporous polypropylene separator (Celegard 2400) was used as a separator. The electrolyte consisted of a solution of 1 mol/L LiPF6 in ethylene carbonate (eC)/dimethyl carbonate(DMC)(1:1. In volume) obtained from Vovolyte Chemical Co. Ltd. Pure lithium foil was used as a counter electrode. The cells were assembled in an argon-filled glove-box. Galvanostatic charge-discharge cycles were tested by LAND CT2001A multi channel battery testers at various current densities from 1 to 50 C (1 C= 165 mAh/g) between 4.2 and 2.5 V vs Li*/Li at room temperature. Note that under the test-voltage-range conditions, CNTs or pyrolysis carbon is table and does not react with lithium, nonetheless we include the mass of residual carbon when calculating the specific capacity of CNTs hybrid LiFePO4 material samples by a four-point d.c. method. Four-point conductivity measurements were made on discs of 8 mm diameter and 0.6 mm thickness, and a SZT-2 instrument (Suzhou, China) was used. AC impedance spectrum was measured by a Solatron 1260/1287 Impedance Analyzer in the frequency range from 10 mHz to 100 KHz with a potential perturbation at 10mV