INvestigation On Synthesis And Doping Modification Of Li₄Ti₅O₁₂

In present, carbon material was widely used as anode material for the commercial lithium ion batteries, but the batteries used carbon material as anode have some intrinsic safety problems:firstly, it was prone to separate out lithium metal when the battery was overcharged, which will lead to a short circuit; secondly, there is passivation film on the surface of carbon, which will cause capacity loss; thirdly, the potential of carbon material is very close to that of lithium, whicht will cause decomposition of the electrolyte. Currently, it has been found that the spinel Li4Ti5O12 has more obvious merits than tranditional carbon material, e.g., (1) it is diffcult to separate out lithium metal as the potential of Li4Ti5O12 is about 1.55 V (vs. Li+/Li); (2) it is a "zero-strain" material, so it exhibits excellent cyclic performace; (3) the charge/discharge potential plateau is very flat. Therefore, Li4Ti5O12 is the promising negative material of lithium-ion battery. However, the low inherent conductance (10-13 S/cm) of Li4Ti5O12 restricts its commercial application. In this paper, the electrochemical properties of Li4Ti5O12 were apparently improved by modifying prepariation techniques and cation doping.Firstly, Li4Ti5sO12 powder with a high discharge capacity and good cyclic performance was synthesized by a hydrothermal method using sucrose as assisted combustion. The synthesis conditions of Li4Ti5O12, such as raw material ratio, sucrose content, hydrothermal treatment time and calcination temperature, were investigated in detail. The results indicate that the optimal preparing condition for Li4Ti5O12 powder is 10 wt.% sucrose, hydrothermal reaction 18 h at 160℃and final calcination at 750℃for 2 h. The as-prepared Li4Ti5O12 sample delivers an initial discharge capacity of 164.78 mAh/g and maintains 150.32 mAh/g after 50 cycles at a rate of 0.5 C.Secondly, Li4Ti5O12 sample was also synthesized by a sol-gel method using lactic acid as complexant. It has been found that lactic content, sintered temperature and sintered time will influence the performance of Li4Ti5O12.When the molar ratio of the lactic acid to Ti(OC4H9) ratio is 0.6 and the calcination temperature is 800℃for 18 h, the obtained Li4Ti5O12 has excellent electrochemical performance. The initial discharge capacity is 172.62 mAh/g and remains 151.68 mAh/g after 50 cycles at a rate of 0.5 C.Thirdly, the Li4Ti5CuxO12+x and Li4Ti4₂XNixMnxO12 samples were prepared by a sol-gel route. The influences of doping element on the electrochemical performance of Li4Ti5O12 were systemically studied. It has been found that cation doping can effectively improve the electrochemical performance of Li4Ti5O12. The initial discharge capacity of Li4Ti5Cu0.3O12.3 was 209.15 mAh/g and remained 165.47 mAh/g after 50 cycles at a rate of 0.5 C; Li4Ti4.8Ni0.1Mn0.1O12 displayed 180.41 mAh/g discharge capacity at the first cycle and kept 160.50 mAh/g discharge capacity at 50th cycle at rate of 0.5 C.