| Nowadays, the need for high energy and high power materials applying in Li- ion battery have been drove by the springing up of EV and the enlargement of electronic products. There are some problems hard to cope with both in silicon and tin materials which have been investigated maturely, as well as the traditional carbon materials. The lithium titanate material has an excellent rate capability and a steady charge-discharge voltage plateau, however, its low theoretical specific capacity, which was only 175 m Ah/g, has limited its application in EV. Therefore, it is urgent to find a highenergy and high-power anode materials to meet this needs.The embed potential of Li+ in titanium niobium oxide is 1.64 V vs. Li/Li+, which can avoid the formation of SEI and improve the energy density simultaneously. It can be obtain an reversible capacity of 280 m Ah/g, far more than that of lithium titanate, when cycling between 1.0 V and 2.5 V. All the advantages above have been attracted researchers domestic and abroad. But its poor conductivity stil l need to be solved. In this article, we studied the synthesis of this material and the doping modification of CNT and Nb, while combining with first-principles calculation, to improve the performance of this material.First, we compared the different synthesis method, i.e. solid, liquid and sol- gel method. By using a sol-gel method, the as-prepared material with a micro- nano hierarchical structure had a reversible specific capacity of 230 m Ah/g and 175 m Ah/g under the rate of 1 C and 5 C respectively after 100 cycle. When CNT was introduced, the specific capacity of materials prepared by liquid method decayed from 212.8 m Ah/g to 172.9 m Ah/g after 100 cycle under 0.1 C, but its only 53.1 m Ah/g for pure phase material. Capacity retention rate of the Ti Nb2O7@5%CNT composites prepared by sol-gel method was 86.94% under 0.1 C, and 94.8% under 1 C, which was higher than 60.50% and 89.20% of Ti Nb2O7. After introduced CNT, conducting matrix was formed, thus enhancing the conductivity along with the cycle stability.Nb-doped materials Ti1-x Nb2+x O7(x = 0.04, 0.06, 0.08, 0.1, 0.12, 0.14), which were prepared by solid phase method, had a similar morphology with Ti Nb2O7, and an uniform and fine particle size dispersion. Cycle performance test results under 1 C showed that Ti0.9Nb2.1O7 have the highest capacity retention rate, holding a reversible specific capacity of 171.78 m Ah/g after 100 cycle. Long cycling test results under 10 C were consistent with that of 1 C, capacity retention rate was 89.42% after 1000 cycle, with respect to the highest reversible specific capacity. Further increasing the content of Nb, Non-stoichiometric compounds Ti1-x Nb2+x O7(x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6) were obtained by sol- gel method. This materials consisted of large micron particles, which were aggregated from small nano particles, formed a micro- nano hierarchical structure, result in a better cycle performance under high rate.First-principles calculations indicated that the band gap are narrowing in Ti Nb2O7 both with Nb-doped and different stoichiometric ratio of Ti and Nb. Materials with 0.5% Nb-doped had a band gap decrease from 2.002 e V to 0.739 e V. And with the increasing of Nb, a broader band gap and a sharper peaks in the DOS was obtained, illustrating an enhancement in microstructure system delocalization and an improvement in conductivity. |
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