Synthesis And Modification Of Lithium Titanate Anode Material For Lithium Ion Battery

The intercalation voltage of current commercially used carbon anode material is 0⁰.26 V, which is very close to the deposition potential of lithium metal, and easy to dissolve out lithium dendritic crystal, as the dendritic crystal grows, it is very possible to puncture the membrane between the cathode and anode electrode, thus result in short circuit in the battery. Spinel Li₄Ti₅O₁₂ with the Ti⁴⁺/Ti³⁺ redox couple appeared at approximately 1.55 V can avoid this disaster, and no lithium dendritic crystal between the discharge process, thus obviously improved the security performances. Because of the perfect cyclic properities, so-called zero-strain material, low cost and the outstanding safety performances, spinel Li₄Ti₅O₁₂ has become a research highlight among various anode materials, and it has been ranked as the secondary anode material for lithium ion batteries by Department of Energy, USA. In this thesis, TG, DTA, XRD, SEM, charge-discharge test, CV, EIS etc are employed to investigate the structure and electrochemical perporties of Li₄Ti₅O₁₂.Spinel lithium titanate oxide is synthesized via solid state method. n(Li)/n(Ti) sintering temperature and sintering time are investigated, the structure and electrochemical performances of different conditions are examined. The results indicate the best synthesizing condition is n(Li)/n(Ti) = 0.86, under 800℃when the sinter time is 12 h, the compound synthesized at this condition shows the best structure and electrochemical performances, not only the symmetrical particle size but the excellent electrochemical properities. When charged at 0.5 C, the initial discharge capacity reaches 150.76 mAh?g^-1, and the initial charge capacity reaches 139.79 mAh?g^-1, the charge capacity keeps at 142.38 mAh?g^-1 after 30 cycles, and the capacity retention is 101.85%.However, spinel Li₄Ti₅O₁₂ exhibits inadequate electronic conductivities that negatively impact its electrochemical performance, this disadvantage limits its commerical use in high current applications for future hybrid electric vehicles. Li₄Ti₅O₁₂/C synthesized by solid state method has been examined in order to improved the electronic conductivities. Different sucrose additions at m(sucrose)/m(Li₄Ti₅O₁₂) = 5%, 10%, 15% are investigated along with the structure and electrochemical performances. The results show that the best sucrose addtion is 10%, when sintered at this condition, the distribution of particles size and electrochemical performance of the compound are the most satisfying. When charged at 0.5 C, the initial discharge capacity is 167.72 mAh?g^-1, and the initial charge capacity is 162.28 mAh?g^-1, and it shows the longest and flattest discharge performance among the three synthesized samples.As a negative material, the capacity of anode materials at low voltage can offer a higher voltage and reversible capacity for lithium-ion batteries, some literatures have shown that Al-doping can cause the discharge platform of Li₄Ti₅O₁₂ to be lower than 1.55V. With these considerations, Li₄Ti_4.95Al_0.05O₁₂/C compound is synthesized. XRD, SEM, electronic conductivity, charge-discharge testing, CV and EIS tests are employed to examine the structure and eletrochemical properities. The synthesized compound has been charged at 0.2C between 0-2.5 V and 1-2.5 V. The results show that Al-doped Li₄Ti₅O₁₂/C has a spinel structure, and the peaks shifted to high degrees, Al-doping considerably improved the electronic conductivity, the initial capacity and cycling performance. The discharge capacity reached 248 mAh?g^-1 after 50 cycles for the Li₄Ti_4.95Al_0.05O₁₂/C while it decreased to 226 mAh?g^-1 for the Li₄Ti₅O₁₂/C discharged to 0 V. Li₄Ti_4.95Al_0.05O₁₂/C and Li₄Ti₅O₁₂/C has a nearly equivalent discharge capacity after 50 cycles at the voltage range of 1.0-2.5 V, indicating that the improving effect of Al-doped discharged to 1.0 V is not obviously. Al-doped improved the reversible capacity and cycling performance effectively especially when it is discharged to 0 V.