Study On Synthesis And Modification Of Ti-based Anode Materials

Ti-based anode material(TiO2 and Na2Ti3O7) with its inherent chemical stability, minimal toxicity, low cost, and high safety has been considered as one of the most suitable candidates for lithium ion batteries(LIBs) and sodium ion batteries(NIBs) anode materials. Although anatase phase have many advantages, there are still problems, such as low lithium and sodium diffusivity and poor conductivity, which will affect the lithium and sodium insertion and extraction rates and restrict its widespread applications. As a newly used anode material, Na2Ti3O7 also suffers from structural distortion, low electronic conductivity and poor electrochemical stability upon sodium insertion/extraction. This thesis is focused on improving the electronic conductivity and electrochemical performance of TiO2 and Na2Ti3O7.Anatase TiO2 nanoparticles have been successfully synthesized via a facile hydrothermal method. The results showed that anatase Ti O2 with nanostructure had the best electrochemical performance in LIBs. In order to overcome their low electronic conductivity, a doping process with functionalized carbon nanotubes(FCNTs) has been used to form TiO2/FCNTs nanocomposites with different wt.% ratios. The results showed that FCNTs as functional component were interpenetrated into the TiO2 nanoparticles and provided a sufficient electronically conducting network, which is greatly improved the electronic conductivity of TiO2. Among these different wt.% ratios, 2 wt.% TiO2/FCNTs showed superior rate performance than other wt.% ratios. The initial discharge capacity of 2 wt.% TiO2/FCNTs is 109.2 mAh g-1, with almost no capacity loss after 100 cycles at a current density of 5040 mA g-1(30 C) in the voltage range of 1.0~3.0 V.Bicrystalline titanium dioxide spheres(anatase@TiO2(B) spheres) with enhanced electrochemical activity in lithium and sodium ion batteries have been successfully synthesized via a facile one-pot solvothermal method. The anatase@TiO2(B) spheres show excellent lithium storage performance, which have high initial discharge capacity(114.8 mAh g-1) with almost no capacity fading after 100 cycles and still maintain at 91.7 mAh g-1 after 375 cycles at a super-high current density of 5040 mA g-1(30 C). On the other hand, the excellent electrochemical sodium storage properties of anatase@TiO2(B) spheres have also been proved. After deep cycling at 850 mA g-1, a capacity of 168.6 mAh g-1 is fully restored upon reducing the rate to 85 mA g-1, and the discharge capacity remains at 131 mAh g-1 at the rate of 170 mA g-1 after 50 cycles between 0.01 V and 2.5 V in NIBs.A novel sodium titanate-carbon(Na2Ti3O7/C) composite has been successfully synthesized via a rheological phase method. The uniformly distributed carbon forms a good network of electrically conductive paths among the Na2Ti3O7 particles, which is closely interlinked with each other. The Na2Ti3O7/C composite exhibits much better electrochemical performance than bare Na2Ti3O7, which displays a stable discharge capacity of 111.8 mAh g-1 at 1 C(178 mA g-1 was assumed to be 1 C rate) after 100 cycles, while only 48.6 mAh·g-1 for bare Na2Ti3O7 at the same conditions.