Synthesis and Mechanism of Tetracalcium Phosphate from Nanocrystalline Precursor

Tetracalcium phosphate (TTCP, Ca4(PO4)2O) was prepared by the calcination of coprecipitated mixture of nanoscale hydroxyapatite (HA, Ca10(PO4)6(OH)2) and calcium carbonate crystal (CaCO3), followed by cooling in the air or furnace. The effect of calcination temperature on crystal structure and phase composition of the coprecipitation mixture was characterized by transmission electron microscope (TEM), thermal analysis-thermogravimetry (DTA-TG), X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), and Raman spectroscopy (RS). The obtained results indicated that the synthesized mixture consisted of nanoscale HA and CaCO3 with uniform distribution throughout the composite. TTCP was observed in the air quenching samples when the calcination temperature was above 1185°C. With the increase of the calcination temperature, the amount of the intermediate products in the air quenching samples decreased and cannot be detected when calcination temperature reached 1450°C. Unexpectedly, the mixture of HA and calcium oxide was observed in the furnace cooling samples. Clearly, the calcination temperature and cooling methods are critical for the synthesis of high-purity TTCP. The results indicate that the nanosize of precursors can decrease the calcination temperature, and TTCP can be calcinated by low temperature

Carbon-Coated Li3V2(Po4)3 Derived From Metal-Organic Framework As Cathode For Lithium-Ion Batteries With High Stability

Recently, Metal-Organic Frameworks (MOFs) derived carbon-based materials have attract wide interest in electrochemical devices due to their large surface area and favorable conductivity. In this work, instead of using MOFs for direct carbon sources, we employed vanadium metal-organic framework (MIL-101(V)) precursor as both carbon sources and vanadium sources for synthesizing carbon-coated Li3V2(PO4)3 nanocomposites (LVP@M-101). The electrochemical property of LVP@M-101 has been investigated as cathode electrode at a voltage of 3.0–4.8 vs Li+/Li, to compare with Li3V2(PO4)3 prepared using V2O5. It is shown that the composite material displays a remarkably improved electrochemical stability with a high reversible capacity of 113.1 and 105.8 mA h g−1 at the rate of 0.5C and 1C after 1000 cycles, together with a superior rate performance at various current densities from 0.1C to 10C. Moreover, we have applied ex-situ PXRD and EPR spectroscopy to investigate the lithiation/delithiation process of LVP@M-101 electrode. Through detailed characterizations and electrochemical tests, we believe that the novel nanocomposites LVP@M-101 retain the two-phase transition nature of Li3V2(PO4)3 and the enhanced cathodic performance in lithium-ion battery is largely due to its unique structural stability