| As an anode material of lithium ion battery,Li4Ti5O12 exhibits good thermal stability,high electrochemical security and long cycling life compared with graphite and other carbon electrode materials.It is considered to be a potential anode material for high-power lithium ion battery.Unfortunately,the inherent low electronic(10-13 S cm-2)conductivity,which leads to the capacity decaying and poor rate performance under the high current charge and discharge process,greatly hinders its practical application.In order to enhance the specific capacity and rate capability of Li4Ti5O12,the Li4Ti5O12/graphene composites have been successfully prepared by three solid-state methods.X-ray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),transmission electron microscope(TEM),Raman spectra,X-ray photoelectron spectroscopy(XPS),electrochemical impedance spectroscopy(EIS),galvanostatic charge-discharge tests and electrochemical workstation were used to confirm the structure and electrochemical performance of the materials.The results of the study are shown as follows:Li4Ti5O12/graphene(LTO-G)and Li4Ti5O12/N-doped graphene(LTO-NG)composites have been synthesized by an two-step ball milling method.Compared with the graphene,the nitrogen doped graphene can provide more free electrons and improve the electronic conductivity of LTO-NG.Comparing the electrochemical performances of the three materials,the LTO-NG exhibits excellent rate capability and cycling stability,with specific capacities of 164,161.5,157.9,144.6,127.8,104.4,and 80.5 mAh g-1 at rates of 0.2,0.5,1,3,5,10,and 20C,respectively.Moreover,LTO-NG shows a charge capacity retention of 92%after 200 cycles at a rate of 5C.Cyclic voltammetry(CV)tests show that LTO-NG has a smallest polarization degree and a largest Li+ diffusion coefficient(5.76 × 10-10 cm2 s-1).Li4Ti5O12/graphene composites with different amount of graphene have been synthesized by an one-step solid-state ball milling and spray drying method.When the amount of graphene is added to 1 wt.%,the Li4Ti5O12/graphene composite(LTO-G-2)exhibits excellent performance with charge capacities of 172.9?165.7?163.5?157.4?154.0 and 143.5 mAh g-1 at 0.2,0.5,1,3,5 and 10C(1C = 160 mAh g-1).Moreover,LTO-G-2 shows a charge capacity retention of 94.8%after 200 cycles at 5 C.Cyclic voltammetry tests(CV)show that the polarization degree of GLTO-2 is the smallest.Electrochemical impedance(EIS)tests also show that the charge transfer resistance of LTO-G-2(69.6 ?)is the lowest.Li4Ti5O12/graphene composites with different amount of graphene have been synthesized by an one-step sand milling method.When the amount of graphene is added to 0.93 wt.%,the Li4Ti5O12/graphene composite(GLTO-2)exhibits excellent performance with charge capacities of 175.2,175.8,171.9,167.9,166.4,164.1,161.4,159.4,and 150.8 mAh g-1 at 0.2,0.5,1,3,5,10,15,20,and 30C(1C = 160 mAh g-1).Moreover,GLTO-2 shows a charge capacity retention of 89.4%after 900 cycles at 10 C and 80.2%after 2000 cycles at 5 C.Cyclic voltammetry tests(CV)show that the polarization degree of GLTO-2 is the smallest and the Li+ diffusion coefficient(1.04 ×10-9 cm2 s-1)is the largest.Electrochemical impedance(EIS)tests also show that the charge transfer resistance of GLTO-2(47.3?)is the lowest. |
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