Study On The Electrode Synthesis Of Titanium - Containing Lithium - Ion Batteries By Hydrothermal Method And Their Electrochemical Properties

More and more people are concerned with the increasing energy consumption and the environmental problems caused by the combustion of fossil fuels. Human being’s demand for green energy is becoming more and more urgent. In the past ten years, lithium ion battery technology is growing rapidly, which has become one of the main energy storage and conversion technology in today’s society.As a very important part of the lithium ion battery, the performance of the anode material directly determines the performance of the lithium-ion battery. TiO₂ is a kind of titanium containing lithium ion anode material, which has the advantages of high capacity, rich resources, environmental friendliness, good structural stability and high safety performance. It’s a new generation of anode materials for lithium ion batteries.However, the electronic conductivity of TiO₂ quite is low （10-12～10-7 s·cm-1）, and once Li+ embedded in the lattice of TiO₂, it would be difficult to form effective ele-ctric field in the surface of lattice. Consequently, Li+ can not be successfully prolapse and lithium ion diffusion rate decreases （10-15～10-9 cm2·s-1） the actual capacity is not high under the high rate charging and discharging. Another Ti containing lithium ion battery anode material is spinel Li₄Ti₅O₁₂. Spinel Li₄Ti₅O₁₂ belongs to an insulation materials, which has a rather low electronic conductivity and ionic diffusion rate.When used as electrode material, there is often a large polarization, and the rate performance is poor. To solve the above problems existed in TiO₂, Li₄Ti₅O₁₂, we use the hydrothermal synthesis method, micro emulsion assisted hydrothermal method, ion doping, etc. to prepare and modify TiO₂ nano structure. The specific research results are as follows:（1） TiO₂ nano particles was prepared by hydrothermal method. The as-prepared TiO₂ nano particals reacted with different concentrations of NaOH/KOH（aq） under a variational temperature and reaction time to get the different morphologies of TiO₂.Electrochemical tests showed that compared with the other four TiO₂ nano struc-tures （nanotubes, nanowires, nanosheets, nanorods）, anatase-TiO₂ nanoparticles have higher first discharge capacity（up to 260.5 mAh·g-1）; a longer voltage platform; the capacity retention rate is high, in 20 mA·g-1 current density discharge, after 50 cycles capacity is up to 200.9 mAh·g-1. The AC impedance of TiO₂ nanoparticles is also the smallest of the five TiO₂ nanostructures, only 40.5 Ω.（2） Due to the TiO₂ nanoparticles has the optimal electrochemical performance among the five kinds of TiO₂ nanostructured, we choose the TiO₂ nanoparticles as we next step materials. We adding seven water ferrous sulfate as the iron source to prepare the Fe doped TiO₂ nanoparticles （Fe/Ti molar ratio of 0.001,0.005,0.01,0.02）. Electrochemical performance test showed that the Fe doped TiO₂ nanoparticles were superior to those of pure TiO₂ nanoparticles in reversible capacity, rate capability and cycle stability. Among the four different Fe doped TiO₂ nanoparticles, Fe/Ti molar ratio of 0.01 of the samples with the best comprehensive electrochemical performance.（3） TiO₂ and Li₄Ti₅O₁₂ are Ti containing lithium ion battery anode material. In this study, Li₄Ti₅O₁₂ nanorods materials coated with anatase TiO₂ were synthesized by microemulsion-aided hydro- thermal method,and the growth mechanism of the composite material was also analyz ed. Electrochemical tests show that when the current density is 0.0175 A·g-1, TiO₂/Li4 Ti5O12 composite reversible capacity up to 209.1 mAh·g-1, even at the current density of 7 A·g-1 and capacity also can reach 102.9 mAh·g-1, which is much higher than pure Li₄Ti₅O₁₂ （52 mAh·g-1）. When the current density 1.75 A·g-1, after 50 cycles, it can keep initial capacity of 96%. These results are showed on the Li4TisO12 coated a layer of anatase type TiO₂ greatly enhance the reversible capacity, rate performance and electrochemical reversible of Li₄Ti₅O₁₂.