Preparation Of Pyrophosphate And Nasicon-Type Phosphate Electrode Materials And Their Electrochemical Performance For Ion Batteries

Ti-based pyrophosphate and Nasicon-type phosphate ion electrode materials have been subjected to extensive research due to their superior characteristics, such as excellent thermal stability and stable three-dimensional framework which are beneficial for ion transport.In this thesis, polyhierarchically structured TiP2O7/C microparticles constructed by carbon-coated nanoflakes encasing crystalline nanoparticles have been prepared by directly annealing flower-like titanium hydrogen phosphate hydrate (Ti(HPO4)2·xHO, THPH) microparticles, which are produced with tetrabutyl titanate and phytic acid in an ethanol-thermal medium. Typical cubic TiP2O7/C microparticles were characterized with XRD, FT-IR, RAMAN, SEM, TEM, TG/DSC and BET techniques. A reasonable formation mechanism of the flowerlike THPH microparticles is proposed on the basis of time-dependent experimental results and theoretical calculations. It is found that carbon layer plays a crucial role in the formation of TiP2O7/C polyhierarchical architecture. When cycled at 1C for 100 cycles,2C for 200 cycles, and 5C for 400 cycles, the TiP2O7/C microparticles exhibit exceptional reversible specific capacities of 128,123, and 90 mA h g-1 with capacity retention of 95.1%,93.2%, and 94.4%, respectively. These results show that the as-prepared TiP2O7/C microparticles has superior electrochemical performance for Li-ion batteries.Carbon coated LiTi2(PO4)3 nanoparticles were synthesized by a coprecipitation method followed by anneal treatment. In the coprecipitation procedure, tetrabutyl titanate, lithium hydroxide, and phytic acid were mixed in ethanol aqueous solution (ethanol/water=1:1, v/v) to produce the precursor. The precursor was collected by filtration and dried, and then subjected to anneal treatment at 750℃ for 4 h. The as-obtained LiT12(PO4)3/C nanoparticles were characterized with XRD, Raman, FT-IR, SEM, TEM, TG/DSC and BET techniques, and tested in the role of electrochemical performance for Li-ion batteries. It is found that when cycled at 5 C for 1000 cycles, 10 C for 1000 cycles, and 30 C for 1700 cycles, the LiTi2(PO4)3/C nanoparticles exhibit exceptional reversible specific capacities of 119,80 and 60 mA h g-1 with capacity retention close to 100%, respectively. The excellent electrochemical of the sample ensures a promising candidate for application in Li-ion batteries.