Studies On The Preparation Of Titanium Based Materials And The Electrochemical Performance

Because of the small size,long cycle life,high energy density and nontoxicity,lithium ion batteries have been widely applied in the electric devices such as mobile phones,digital cameras,laptops and electric vehicles.Generally,Carbon materials were utilized as the anode materials for the Commercialized lithium ion batteries.However,the low voltage window(-0.1 V vs Li+/Li)of the carbon anode easily leads to the growth of lithium dendrites,which probably causes the safety issues.So it is urgent to search the candidates for the commonly used carbon anode.Spinel Li4TisO12,can effectively avoid the generation of lithium dendrites as a result of the higher voltage window(-1.5 V Li+/Li),with the advanteges of zero-strain characteristics and stable electrochemical properties,is the ideal candidate for the carbon anode.Nevertheless,the low theoretical capacity combined with sluggish electric conductivity(<10-13 S cm-1)and lithium ion diffusion coefficient(10-14-10-17 cm2 s-1)for the Li4Ti5O12 severely impedes the further applications.We have successfully prepared the porous Li4Ti5O12-TiO2 nanosheet arrays by virtue of the hydrothermal method.The electrochemical performance of the Li4Ti5O12-TiO2 electrode have been significanlty improved with the introduction of TiO2.At a current density of 200 mA g-1,the Li4Ti5O12-TiO2 electrode showed a initial capacity of 184.6 mAh g-1.After 1000 cycles at a current density of 1 A g-1 only the capacity loss of 8.3%is derived for the Li4Ti5O12-TiO2 electrode.Simutaneously,we fabricated the sandwitch like TiO2@ZnO arrays with the porous interconnected nanostructure.The TiO2@ZnO electrode delivered more excellent electrochemical performance than that of the individual TiO2 and ZnO electrodes,whose capacity reach up to 340.2 mAh g-1 at the current density of 200 mA g-1 after 100 cycles.Even at a high current density of 1600 mA g-1,The TiO2@ZnO electrode have the capacity of 205.2 mAh g-1.Lithium ion batteries can not fullfil the requirement of rapid charge-discharge process because of the poor power density.Lithium ion supercapacitors can combine the advantages of lithium ion batteries(high energy density)and supercapacitors(high power density).N-CNTs and hierarchical RLTO nanosheet arrays with a 3D interconnected architecture have been successfully fabricated.From the aspect of morphology,the hierarchical 3D open interconnected structure of RLTO nanosheet arrays provides open channels for lithium ions and electrons as well as effectively mitigates the aggregation because of the stable interconnected construction.From the aspect of the crystal structure,the exposed(011)facets of LTO and(001)facets of rutile TiO2 in the RLTO composite provide efficient lithium diffusion channels.The above mentioned advantages guarantee the excellent electrochemical performance of the RLTO electrode with a reversible specic capacity of 142.9 mA h g-1 and 92.3%retention of its initial capacity at a rate of 30 C over 3000 cycles.The RLTO anode with competitive rate capability matches well with the high surface-area N-CNT cathode even at a high current density for LIC,and an ideal electrochemical performance is realized with a superb energy density of 74.85 W h kg-1 at a power density of 300 W kg-1.The relatively low energy density(-150 Wh kg-1)of lithium ion batteries can not meet the ever-increasing requirement for the high energy density especially in the field of electric vechicles.Lithium-sulfur(Li-S)battery is of great interest as a next-generation energy storage solution due to the ultra-high theoretical energy density(2600 Wh kg-1)and specific capacity(1675 mA h g-1),particularly for electric vehicles.Graphene-assisted TiO2-S interconnected frameworks were successfully designed,fabricated and used as the cathode materials for Li-S batteries.The hierarchical architectures of TiO2 sphere with overlapped subunits of nano(?)akes can effectively accommodate sulfur nanoparticles.Therefore,the volume expansion and nanoparticle aggregation can be effectively mitigated,thereby facilitating the sulfur utilization rate.Further modication of graphene for the TS composite can not only improve the electronic conductivity,but also signicantly provide the effective pathways for the Li+ ions and electrons and suppress the diffusion of polysuldes to electrolytes,thus providing excellent cycling stability and high coulombic efficiency.In addition,the chemical bond detected in the GTS products between graphene and sulfur can efficiently stabilize polysulfides on the cathode.The graphene-assisted TiO2-S composite electrodes exhibit high specific capacity of 660 mAh g-1 at 5 C with a capacity loss of only 0.04%per cycle in the prolonged charge-discharge processes at 1 C.The rarity of lithium sources severely impedes the further application of LIBs.Sodium-ion batteries(NIBs)as the competitive alternatives to LIBs,have aroused intensive interest particularly for large-scale stationary energy storage applications,on account of the infinite sodium resources and low cost.Nanoparticle-stacked SLTO nanowire arrays have been successfully designed for NIBs.A competitive rate performance(92.4 mAh g-1 at 15 C)is also obtained for the SLTO electrode when applied in NIBs.Most importantly,the sodium ion full battery exhibited tiny degradation even after 200 cycles at 4 C with a capacity of 90.1 mAh g-1 possessing a high energy density of 136.5 Wh kg-1 at the power density of 312 W kg-1.