Among the commercial anode materials, graphite isn`t suitable for high-power applications such as electric vehicles and large-scale energy storage due to formation of the solid-electrolyte interphase (SEI) leading to lithium irreversibly at about 0.8V and inactive high rate performance. Although, Li₄Ti₅O₁₂ (LTO) are being pursued as alternatives to graphite electrodes due to high lithium storage voltages (1.0~2.0V) which are higher than the formation of SEI voltage and high rate capability, it has low theoretical capacity (~175mAhg^-1). Recently titanium-niobium oxides (TNO) such as TiNb₂O₇, Ti₂Nb₁₀O₂₉ with high redox potential range have been considered as interesting candidates for anode material of LIB. Because they have higher theoretical capacity of 380~396mAhg^-1 due to multiple redox couples such as Ti⁴⁺/Ti³⁺, Nb⁵⁺/Nb⁴⁺, Nb⁴⁺/Nb³⁺ by compared with LTO having only Ti⁴⁺/Ti³⁺ redox couple. In addition, they have good stability, high rate capability. However, they are show limited reversible capacities (240~270mAhg^-1) owing to low electronic conductivity and lithium diffusion coefficient. Chunfu Lin et al. presented that TiNb₆O₁₇ showed higher capacity, lithium diffusion coefficient and high rate performance than Ti₂Nb₁₀O₂₉. Because it is consist of larger amount of Nb⁵⁺ ions with larger size (0.64A) than that of Ti⁴⁺ ions (0.605A). As a result, it has more open lithium insertion structure and lithium diffusion coefficient than Ti₂Nb₁₀O₂₉. But this study not exactly proposed chemical properties such as oxidation state, lithium insertion behavior of TiNb₆O_17.

Based on above study, we have compared physical properties and electrochemical performance of new compound TiNb₆O₁₇ and TiNb₂O₇ which were fabricated using a solid-state reaction method. In a typical synthesis, TiO₂ and Nb₂O₅ in the molar ratio (1:2, 1:6) were mixed with ethanol in a ball mill at 300rpm for 4h. After drying, calcination treatment is carried at 1100°C for 10h in air atmosphere. The crystal structures were determined by X-ray diffraction (XRD), rietveld refinement in order to compare lattice parameters and unit cell volume. X-ray absorption spectroscopy (XAS) was measured to confirm variation of oxidation state and lithium insertion/extraction behavior after charge and discharge. The morphologies were observed by scanning electron microscope (SEM). Finally, we investigated electrochemical performance by measuring cyclic voltammetry, galvanostatic charge-discharge curve and C-rate. Also, electrochemical impedance spectroscopy (EIS) and slow scan rate cyclic voltammetry (SSCV) were measured to compare lithium diffusion coefficients of TiNb₂O₇ and TiNb₆O₁₇. As the result of, TiNb₆O₁₇ exhibited better electrochemical performance with lithium diffusion coefficient, charge-discharge capacities and high rate performance than TiNb₂O₇.