[en] Highlights: → Carbon gel has an important influence on the electrochemical properties of the LiFePO₄ materials. → By using the carbon gel, the lithium ion diffusion was enhanced due to the increase of the Li-O interatomic distance and the cross section area of the lithium ion one-dimension tunnel. → In addition, the electric conductivity was obviously increased due to the small grains and good grain contact. - Abstract: Lithium iron phosphate (LiFePO₄) cathode material has been synthesized by a solid-state reaction. The XRD patterns and SEM images of the samples show that the LiFePO₄ compounds prepared at 650 deg. C by using carbon gel in reaction have a single-phase, small grain-size and regular shapes. By using Rietveld refinement method, we calculated the Li-O interatomic distance in LiO₆ octahedra and the cross section area of the lithium ion one-dimension tunnel, and analyze the reason of the improvement of the Lithium ion diffusion. The electrochemical test results of the sample show the LiFePO₄ prepared by using carbon gel exhibits excellent electrochemical properties. Such a significant improvement in electrochemical performance should be partly related to the enhanced Lithium ion diffusion and electric conductivity due to the use of carbon gel.

[en] Phase equilibria in the ternary Li₂O-FeO-B₂O₃ system were studied by means of X-ray powder diffraction. The Li₂O-FeO-B₂O₃ system can be characterized by the existence of 17 three-phase regions. For the two ternary compounds found in this system, the compound A with molar ratio of Li₂O, FeO and B₂O₃ in 2:1:1 had not been reported previously. The nearly unchanged d values for the X-ray diffraction peaks of the samples around the new compounds A indicate the existence of the new compound A in the ternary Li₂O-FeO-B₂O₃ system. Other new information includes the electrochemical properties of LiFeBO₃ compound, where the electrochemical test indicated that the discharge plateau potential of LiFeBO₃ compound is around 2.3 V and initial discharge-specific capacities can reach to 91.8 mA h g^-1. Our results show that LiFeBO₃ samples have better capacity retention except for the first two cycles

[en] Lithium iron phosphate (LiFePO₄) cathode material has been synthesized by a solid-state reaction. The XRD patterns of the samples show that the single-phase LiFePO₄ compounds can be obtained in our experimental conditions. According to Popa theory, using the result from Rietveld refinement, the shape and the size of crystallite can be obtained. The result shows that the use of carbon gel in precursors do not change the structure of the crystal, but it can inhibit the particle growth and restrain the anisotropy growth of the grain at a lower temperature. At a higher temperature, carbon-coated LiFePO₄ shows an anisotropy growth, i.e. growth rate along (1 0 0) crystal plane is more rapid than that of (1 1 1) crystal plane. In our experimental conditions, a spherical carbon-coated LiFePO₄ can be synthesized successfully at 650 deg. C. The electrochemical testing indicated that the spherical carbon-coated LiFePO₄ had the excellent performance. Its initial specific capacities were 156.7 mAh g^-1 under the rate of C/10. At the 50th cycle, the reversible specific capacities were found to approach 151.2 mAh g^-1 (the ratio of 96.5% of initial capacity)

[en] LiFeBO₃ cathode material has been synthesized successfully by solid-state reaction using Li₂CO₃, H₃BO₃ and FeC₂O₄.2H₂O as starting materials. The crystal structure has been determined by the X-ray diffraction. Electrochemical tests show that an initial discharge capacity of about 125.8 mAh/g can be obtained at the discharge current density of 5 mA/g. When the discharge current density is increased to 50 mA/g, the specific capacity of 88.6 mAh/g can still be held. In order to further improve the electrochemical properties, the carbon-coated LiFeBO₃, C-LiFeBO₃, are also prepared. The amount of carbon coated on LiFeBO₃ particles was determined to be around 5% by TG analysis. In comparison with the pure LiFeBO₃, a higher discharge capacity, 158.3 mAh/g at 5 mA/g and 122.9 mAh/g at 50 mA/g, was obtained for C-LiFeBO₃. Based on its low cost and reasonable electrochemical properties obtained in this work, LiFeBO₃ may be an attractive cathode for lithium-ion batteries

[en] Using first-principles method we studied the compensation mechanism of As donor in Hg_1-xCd_x Te based on the model Berding et al. (1998, 1999) of As_Hg-V_Hg pair. We show that the binding of As_Hg and V_Hg results from donor-acceptor coupling, and the compensation of As donor can be clearly explained in terms of electronic deactivation by V_Hg. The pairing physics derived from this study confirm the available theoretical and experimental results.