Design And Preparation Of Titanium Dioxide Anode Materials For Lithium-Ion Batteries And Electrochemical Performance

Rechargeable Li-ion batteries（LIBs） are now widely considered the most important power sources for various portable electronic devices, electric vehicles（EVs） and hybrid electronic vehicles（HEVs）. But commercial lithium-ion batteries still cannot meet the needs of high power equipment. However,commercial Li-ion batteries still cannot satisfy the requirements of those large-scale power sources. They encounter the necessity of breakthroughs in terms of power/energy densities, safety, and long-term stability.Although graphite electrode has been widely used in commercial lithium ion battery cathode, but it has serious safety problems including dendritic growth of Li due to the low operating voltage（⁰.2 V vs.Li/Li+）. As a result, numerous efforts have been devoted to developing safe, high-performance transition-metal oxide anode materials.In this respect, TiO₂ has attracted significant attention because of its relatively high lithium insertion/extraction voltage（ 1.6 V vs. Li/Li+）. In addition, its low volume variation（<4%） during the lithiation/delithiation process favors large-scale energy storage. Unfortunately,TiO₂ has poor electronic and ionic conductivity that limits its application as a high power anode material.So we design and prepare three different composites to solve these problems in this thesis.（1） A facile and green strategy for the synthesis of a few-layer reduced graphene oxide（FL-RGO）-wrapped mesoporous anatase TiO₂（m-TiO₂） submicrosphere（denoted as m-TiO₂@FL-RGO）composite was developed via glucose-assisted hydrothermal GO reduction and TiO₂ crystallization. In this approach, glucose is important for tightly immobilizing FL-RGO on the surface of the m-TiO₂ submicrospheres. The wrapping of FL-RGO improves the electrochemical kinetics of the m-TiO₂ submicrospheres, which results in superior electrochemical performance in terms of specific capacity, rate capability and cycle stability. The material shows a discharge capacity of 202.5 m A h g-1 at 0.6 C after 100 cycles. Even at a current rate of 30 C, a high discharge capacity of 113.5 m A h g-1 is still obtained, which is two-fold higher than that of pristine m-TiO₂ submicrospheres.（2） Then, we prepared graphene oxide supported TiO₂-B（TiO₂-B-GO） composites by one-step hydrothermal method. N-doped TiO₂-B/N-doped Graphene composites（N-TiO₂-B/NG） were prepared by a facile hydrothermal combined with hydrazine monohydrate vapor reduction method. From the CV and EIS test, we found that N-TiO₂-B/NG composites has more excellent dynamics compared with the pristine TiO₂-B,which makes the composite material has high cycle and rate capacity, outstanding performance.The TiO₂-B/NG composites have reversible specific capacity of 333.1 m Ah g-1 at 0.6C after 100 cycles.In addition, it can deliver a discharge capacity of 153.3 m Ah g-1 at an ultra high rate of 50 C, indicating its great potential in high power lithium ion batteries.（3） Finally,unique mesoporous TiO₂-C hollow nanospheres grafted with MnO2nanoparticles（donated as TiO₂-C@Mn O2） is synthesized for the first time as an anode for Lithium-ion batteries. The character of the special structure is Mn O2 nanoparticless grown on the outer and inner surface of the hollow TiO₂-C. The composite combines the advantages both from Mn O2 with high capacity（1230 m Ah g-1） and TiO₂-C with excellent cycle stability and superior electrical conductivity. Besides, the Mn O2 with different account on the surface of hollow TiO₂-C is fabricated through controlling concentration of reactants and it is found that the account of Mn O2 nanoparticles has a significant impact on capacity, cycle performance and conductivity. The TiO₂-C@Mn O2 samples possesses excellent electrochemical properties with good cycle stability and a high specific capacity of 127.9 m Ah g-1 at 12 A g-1.