Synthesis And Morphology Regulation Of Li₄Ti₅O₁₂ Anode Materials By Liquid-phase Method For Lithium-ion Batteries

Lithium-ion secondary batteries are being increasing evaluated for electric vehicle(EVs) and hybrid electric vehicle (HEVs), due to its high energy density and long cycle life.Higher requirements are desired for lithium-ion batteries with the development of newenergy industry. Proper electrode materials are the strategic point for improving theperformance of lithium ion battery.Spinel Li4Ti5O12has attracted considerable attention as an anode material, because ofits zero-strain insertion crystal structure and no SEI layer on the surface of the electrodeduring lithium insertion/extraction, which endow long cycle life and high safety. However,Li4Ti5O12suffers from a major drawback: the poor electronic conductivity (10-13S cm-1).To enhance the electrochemical performance of Li4Ti5O12, in this study, we report asynthesis method to fabricate Li4Ti5O12with unique structures. Main results are shown asfollow.(1) Two-dimensional Li4Ti5O12nanosheets could be formed by the self-assembly ofone-dimensional Li4Ti5O12nanorods. The width of each Li4Ti5O12nanorod is about15nm and the thickness of the Li4Ti5O12nanosheets is in the range of8-25nm. Thenanosheets may be formed by the oriented attachment of the tiny nanorods at theirhigh energy surface. The crystallographic axes of the tiny nanorods in a region areparallel and the Li4Ti5O12nanosheets largen with their growth along and perpendicularto the axed of the nanorods.(2) Well-crystallized Li4Ti5O12nanosheets were synthesized by a facile one-stephydrothermal method. The FESEM images show that the slimmest thickness is about 8nm. The initial discharge capacity at1C rate is207.2mAh g-1, which is muchhigher than the theoretical capacity of Li4Ti5O12(175mAh g-1). After50cycles,82.8%of its initial discharge capacity is retained for the as-prepared Li4Ti5O12nanosheets, indicating the excellent cyclic performance.(3) Li4Ti5O12-TiO2composites were synthesized by a facile hydrothermal method usingPVP as a surfactant. When the content of PVP increases from zero to52wt.%, thediffraction peak of rutile-TiO2strengthen and the thickness of nanosheets enhancefrom10nm to25nm. At1C rate, the initial discharge capacity of196.7mAh g-1canbe obtained for the composites with35wt.%PVP.(4) Li4Ti5O12microspheres with a hierarchical structure were prepared bysol-gel/hydrothermal method using SiO2spheres as the template. When Li/Ti molarratio is0.5, the as-prepared Li4Ti5O12microspheres exhibit the high first dischargecapacity of152.6mAh g-1at1C rate. Li4Ti5O12-TiO2composites with a honeycombstructure were synthesized by template method using C spheres as the template whenthe molar ratio of Li to Ti is1.0. The initial discharge capacity of129.8mAh g-1canbe obtained for the Li4Ti5O12-TiO2composites at the current density of100mA g-1.(5) Discussing the effect of calcination temperature and calcination time to theelectrochemistry performance of Li4Ti5O12, the Li4Ti5O12nano-bulks synthesized at800oC for10h exhibit the best electrochemical performance. The initial dischargecapacity of179.8mAh g-1is maintained at the current density of100mA g-1, which ismuch higher than the Li4Ti5O12-TiO2composites calcined at600oC for2h (118.4mAh g-1). Even after50cycles, the specific capacity of158.2mAh g-1is still obtainedwith88%of the capacity retention.