Synthesis And Properties Of Lithium Titanate Used As Power Battery Anode Material

Lithium-ion batteries are widely used in portable electronic products owning to their advantages of high energy density,no memory effect and dependable safety,and now are gradually moved toward to the fields of hybrid electric vehicles and large-scale energy storage.Lithium titanate with good cycling performance and structural stability is regarded as a promising candidate anode material for lithium-ion batteries.In this thesis,lithium titanate was successfully prepared via a liquid-phase method.Meanwhile,the inherent defects of Li4Ti5O12 has been overcome by ion doping(Na+?Zr4+)and coating with conductive materials(Ag?graphene).The main results are as follows:1.The lithium titanate was successfully synthesized through adopting hydrothermal method.Li4Ti5O12 calcinated at 700 ? for 8 h possessed pure phase and high degree of crystallinity,and delived an initial specific discharge capacity of 167.4 mAh/g at 0.2 C rate.In addition,the Li4-xNaxTi5O12 samples were obtained via Na doping.The XRD results indicated that all samples present spinel structure.The Li3.9Na0.1Ti5O12 exhibited high specific capacity of 153.4 mAh/g at 1 C rate,and maintained 136.8 mAh/g even after 40 cycles with reversible retention was 89.17 %.2.The Li3.9Na0.1Ti5O12/graphene composites were fabricated via a solvothermal method.Graphene sheets were uniformly distributed among the Li3.9Na0.1Ti5O12 particles to make the composites have higher electron mobility.Electrochemical tests revealed that the electrode(3 wt% GO)had good cycle stability and high specific capacity of 158.8 mAh/g at 1 C,and still retained at 146.3 mAh/g after 40 cycles.In addition,Ag fine particle was introduced to lithium titanate through electroless deposition process,highly improved its conductivity.The result demonstrated that Li4Ti5O12/Ag electrode had outstanding electrochemical performance.3.Nanoscale particles of Li4Ti5-xZrxO12 samples were successfully prepared via a solvothermal method,which avoided rapidly hydrolyzing between tetrabutyl titanate and water.The XRD result indicated that some of the dopant Zr atoms entered the lattice of Li4Ti5O12,but did not change the spinel structure.The Li4Ti4.9Zr0.1O12 sample had prominent lithium storage capacity and long-term cycling stability than pristine Li4Ti5O12,delivering an discharge specific capacity of 171.1 mAh/g at 0.5 C,close to the theoretical specific capacity of 175 mAh/g and the reversible retention was still 92.11 % after 40 cycles.4.“Co-hydrolysis” method was adopted to synthesis the two-dimensional sheets of C-Li4Ti5O12 composite with calcining at 600 ? for 3 h in argon filled atmosphere.The C-Li4Ti5O12 composite exhibited large surface area and superior electronic conductivity.As a result,this electrode not only exhibited prominent discharge specific capacity of 186.6 mAh/g at 0.5 C,but also showed impressive high-rate performance.In addition,the extraordinary conductive graphene was introduced to C-Li4Ti5O12 composite,and effectively improved the electrochemical performance of materials.