Gao Mingxia

Synergetic effect of the crystallinity, particle size of LiFePO 4 and the in-situ introduced Fe 2 P on its high-rate capability

LiFePO 4 /C composite with high crystallinity, sub-micron particle size and suitable content of in-situ introduced Fe 2 P was synthesized by a sol-gel method, in which LiOH, Fe 2 C 2 O 4 and NH 4 H 2 PO 4 were used as starting materials, and ethylene glycol was used as complexing agent and carbon source. The precursor of LiFePO 4 was calcined at a comparatively low temperature for relatively long time combined a following calcination at a comparatively high temperature for relatively short time. The composite shows high-rate capability as cathode material for lithium-ion batteries. The structure and the electrochemical properties of the LiFePO 4 /C composites synthesized by different calcination parameters were analyzed by X-ray diffraction, scanning electron microscopy, element analysis and electrochemical testing of galvanostatic charge-discharge, etc. The results show that the step-wise calcination at different temperatures for different times is an effective approach to obtain suitable amount of in-situ Fe 2 P, control the particle size and enhance the crystallinity of LiFePO 4 , which results in a significant improvement in the high-rate capability of LiFePO 4 . The LiFePO 4 /C composite synthesized at a calination temperature of 600℃ for 20 h followed by a further calcination at 700℃ for 4 h has 4wt% Fe 2 P and 3wt% C. The composite possesses discharge capacities of 140, 110 and 100 mAh/g at discharge rates of 1, 10 and 20 C, respectively.

Diffusion, Intrusion and Reaction between Al-Containing Intermetallics and TiC Sintered Body during Thermal Pressure Holding

Intermetallics of Fe40Al, Ni3Al and TiAl(NbCr) were used as matrix to effectively bond a layer of TiC sintered body with low porosity. The coupled intermetallic and the TiC sintered body were held at high temperatures and a given pressure. The microstructure of the interface was observed and analyzed by scanning electron microscopy (SEM) and energy dispersive spectra (EDS). The results show that the bond between the intermetallics and the TiC sintered body is a metallurgical bond. TiC slightly decomposes and diffuses into the surface layers of Fe40Al and Ni3Al during the holding time, resulting in decrease of their melting points, and hence the intermetallic is in a flowing state and intruded into the pores of the TiC sintered body at the interface. However, the TiAl(NbCr) alloy can not be intruded into the pores of TiC sintered body; instead, a distinct reaction layer with more than 10 at% Ti (higher compared with the matrix) is formed at the interface of the TiAl(NbCr) alloy and the TiC sintered body.