Preparation Of Lithium Titanate Composite And Its Electrochemical Properties For Li-ion Batteries

The invent of lithium ion batteries provides a great convenience for human society,but the low potential of traditional graphite anodes(<1.0 V vs Li/Li+)and poor electrolyte matching will make battery combustion,explosion and other accidents.Moreover,the rise of new energy automobile industry puts forward higher requirements for lithium ion batteries,and the poor rate performance and short cycle life of carbon anodes can’t meet the need.Meanwhile,spinel lithium titanate(Li4Ti5O12),a famous"zero strain" material,which shows a super long cycle life,is a kind of promising candidate.But the low conductivity(10-13 S/cm)hinders its business development.In this article,we used β-cyclodextrins and PMMA(polymethyl methacrylate)as carbon sources to prepare Li4Ti5O12/C nanocomposite,then synthesized pure lithium titanate crystal through the hydrothermal method and high temperature solid-state method.Li4Ti5O12/C composite precursors were prepared using β-cyclodextrin or PMMA as the carbon source by the hydrothermal method at 130 ℃ for 24 h and then calcinated at 400 steped by 500 ℃ for 5 h,respectively.The materials are loose,uniformed two-dimensional nanosheets,with the thickness only about 30 nm.The introduction of the two kinds of carbon source improvs the rate performance greatly,which deliver 114.9 mAh/g(β-cyclodextrin)and 141.9 mAh/g(PMMA)at 40 C,respectively.Some impurities,such as different crystal TiO2,mixed in the Li4Ti5O12/C composite.Therefore,on the basis of the hydrothermal method,we prepared pure Li4Ti5O12 crystal by controlling the ratio of Li and Ti.When Li:Ti is 4.5:5,Pure phase spinel Li4Ti5O12 is got,which is porous and uniform distribution of two-dimensional nanosheets,and delivers 128.7 mAh/g at 40 C.When Li:Ti is 4:5 or 4:5.5,different crystal TiO2 exist in the product.In order to explore appropriate conditions of lithium titanate in industrial production process,we used the high temperature solid-state method to synthesize Li4Ti5O12.The temperature and reaction time show a great influence on the structure and electrochemistry performance of the material.When the calcination temperature is less than or equal to 750 ℃ for 12 h,TiO2 and Li2CO3 cannot be reacted thoroughly,and the product contains rutile titanium dioxide.When the calcination temperature is 800 0C and above,TiO2 and Li2CO3 can be reacted thoroughly,and pure Li4Ti5O12 crystal is got.When calcined for 12 h or below at 750 ℃,there are some rutile titanium dioxide mixed in the Li4Ti5O12.However,we could also get pure Li4Ti5O12 when calcined for more than 15 h at 750 ℃.Among all material,the material calcined at 750 ℃ for 6 h shows the best electrochemistry performance,which delivers 95.3 mAh/g at 40 C.Meanwhile,the pure Li4Ti5O12,calcined at 750 ℃ for 15 h,delivers 75.3 mAh/g at 40 C.