Studies On Electrochemical Lithiation And Delithiation Behaviour Of Titanium Dioxide

Titanium dioxide (TiO2) is one of ideal anode materials for Li-ion batteries, demonstrating a theoretical lithiation capacity of335mAh g-1, with higher Li+intercalation potential, good stability, low price and environmentally friendly. The small volume change of TiO2(<4%) after lithiation, affords TiO2outstanding structure stability during lithiation and delithiation cycling. However, the intrinsically poor electronic and ionic conductivities of TiO2greatly decrease its electrochemical performance. Based on review of the recent progress, we developed a new method to synthesize micron secondary nano primary TiO2(MSNP-TiO2), and discussed different carbon sources on the electrochemical performance of TiO2/C, including graphite oxide(GO), polyethylene glycol(PEG) and macroporous carbon (MPC).Spray drying technology was used for preparation of micro-sized TiO2bowls (secondary particle) composed of nano-TiO2particles (primary particle) through tetrabutyl titanate (TBT) hydrolysis. The effects of pH value and TBT concentration in the precursor sols on the morphology and lithiation-delithiation capacity of synthesized TiO2materials are investigated. The formation mechanism of synthesized TiO2materials with special morphologies such as TiO2bowls is discussed. With increasing of TBT concentration in the sol from12to20mL of TBT, the formed TiO2profile changes from the curled shape to bowl. Further increase in TBT content of the sol (up to44mL of TBT) has little influence on the TiO2profile. These samples are named as TBT12, TBT20and TBT44for convenience, respectively. The cross-section view indicates that TBT44has thicker wall than TBT20. The reversible Li+capacity of the TiO2prepared by pyrolysis of spray-dried materials from precursor sols with different TBT contents. The reversible Li capacity of synthesized anatase TiO2(175～185mAh g-1) has affected slightly by the TBT content in sols.For improving the lithiation-delithiation capacity of synthesized micro-sized TiO2materials, carbon is coated to the surfaces of TiO2bowls to improve their electric conductivity. When TiO2bowls were coated with carbon using graphite oxide and PEG as the carbon source, the obtained TiO2/C (carbon content:5wt.%) displays good rate performance. Compared with bare TiCte, the rate capacity (at2C) increases from20to90mAh g-1.It is found that the carbon coating effect on the electrochemical performance improvement depends on the morphology of TiO2particles. Carbon-coating layer shows Li+insertion blockage to TiO2bowls with thin wall, but improves electrochemical performances of bowls with thick wall. The thickness of the TiO2bowls plays an important role in creation Li+pathway in the carbon layer. The discharge capacity of CPEG-TBT44at the rate of0.1C shows a capacity of310mAh g-1, but CPEG-TBT20shows the poor eletrochemical performance (20mAh g-1). Lithiation and delithiation cycling between3.0and0.0V can activate carbon layer on carbon-coated TiO2.Embodying nano-TiO2/C to macroporous carbon (MPC) to form a new type of TiO2-C composite (TiO2/CMPC). The MPC decreases the TiO2grain size and shortens the lithium ion transmission distance, resulting in a better lithium ion conduction. The porous structure of MPC also improves the contact of active material with electrolyte, resulting in the enhanced electrochemical performance. The TiO2/CMPC shows excellent rate capacities and performance stability.