The Preparation Of Electrode Materials For High Electrochemical Performance Lithium-ion Batteries

One dimensional nanofibers among various morphologies of titanium dioxide (TiO2) have attracted particular interest for LIBs owing to their large specific surface area, fast ion and electron transport pathways, and good accommodation of the volume change during the charging/discharging processes. Herein, novel nanocomposites consisting of two-dimensional graphene nanosheets and ultralong TiO2 nanofibers are synthesized via a simple one-pot hydrothermal reaction using commercial TiO2 particles as inorganic precursors. Complex chemical synthesis processes and high cost precursors can be avoided. We have investigated the influences of annealing temperature and atmosphere on the electrochemical performances of the nanocomposites. The results indicate that the atmosphere has little effect on the electrochemical performance of the nanocomposites. Meanwhile, the nanocomposite obtained at 500 ℃ for 4 h in a N2-fowing tube furnace exhibits superior electrochemical performance. When used as anode of lithium ion batteries, the obtained nanocomposite exhibits an excellent rate capability and a superior long-term cycling stability. The nanocomposite maintains a charge capacity of 128 mAhg-1 at 5 C,104 mAh g-1 at 10 C, and 85 mA h g-1 at 20 C, while the pure TiO2 nanofibers fail when cycle at 5 C. The nanocomposite also demonstrate an excellent cycling stability with a charge capacity of 92 mA h g-1 after 1000 cycles at 10 C, approximately three times the capacity of the pure TiO2 nanofibers. The superior electrochemical performance can be attributed to the hybrid structure of the graphene nanosheets and the ultralong TiO2 nanofibers. The graphene nanosheets provide highly electronically conductive pathways and work as protected layers to keep the active material integrating during the charging/discharging processes. The ultralong TiO2 nanofibers with high specific surface area have a short ion diffusion distance and provide more accessible sites. By combining the advantages of the graphene nanosheets and ultralong TiO2 nanofibers, the nanocomposite exhibits obviously improved electrochemical performances.Li9V3(P2O7)3(PO4)2 has recently been reported as a novel cathode material for lithium-ion batteries. Its advantages include high theoretical specific capacity (173.5mA h g-1), low cost, environmental compatibility, and safety. However, the rate capability of unmodified Li9V3(P2O7)3(PO4)2 is significantly restricted by sluggish electron and lithium-ion transport kinetics. To solve this problem, coating with conducting layers, doping with isovalent ions, or reducing the particle size of the electrode material are known to be effective strategies. Recently, microspheres with micro/nanostructure have become highly desired in designing high performance cathode materials for lithium-ion batteries with high volumetric energy density and good rate capability. In this work, we have employed four complexants to synthesize the special microspheres with micro/nanostructure. The SEM results indicated that the monodisperse Li9V3(P2O7)3(PO4)2 microspheres can be successfully obtained by using triethanolamine as complexants through an one-pot hydrothermal approach, each microsphere was formed with nanoplates arranged in an open three-dimensional (3D) mesoporous structure. Conductive polyaniline (PANI) was deposited onto the Li9V3(P2O7)3(PO4)2 microspheres to further increase their rate capability. The PANI layer was found to have a thickness of 2～3 nm through the HR-TEM image. As expected, the Li9V3(P2O7)3(PO4)2/PANI microspheres exhibit a superior rate capability compared to the Li9V3(P2O7)3(PO4)2 at the same testing condition, with the capacity of 110 mA h g-1 at 5 C,95 mA h g-1 at 10 C, and 75 mA h g-1 at 20 C. More importantly, a stable capacity of 137 mA h g-1 can be delivered when the rate is reduced back to 0.1 C, suggesting a good structural stability and high reversibility of the microspheres. Furthermore, the monodisperse Li9V3(P2O7)3(PO4)2/PANI microspheres can remain approximately 110 mA h g-1 at 5 C and 94 mA h g-1 at 10 C for a total of 500 cycles, showing an excellent long-term cycling stability. The Li9V3(P2O7)3(PO4)2/PANI has become a promising cathode material for LIBs due to its superior electrochemical performances, which were generated from the synergistic effect of monodisperse 3D mesoporous microspheres and the high electronically conductive polymer.