Ru0.01Ti0.99Nb2O7 as an intercalation-type anode material with a large capacity and high rate performance for lithium-ion batteriesElectronic supplementary information (ESI) available: Crystal structure of TiNb2O7 showing the m × n × ∞ (m = n = 3) ReO3-type blocks (Fig. S1); Nyquist plots of the Li4Ti5O12/Li cell and Li+ ion diffusion coefficient of Li4Ti5O12 (Fig. S2); Coulombic efficiency of the Ru0.01Ti0.99Nb2O7/Li cell at 5 C (Fig. S3); ex situ XRD patterns of TiNb2O7 electrodes (Fig. S4); S

• Main Authors: Lin, Chunfu, Yu, Shu, Wu, Shunqing, Lin, Shiwei, Zhu, Zi-Zhong, Li, Jianbao, Lu, Li
• Format: Article
• Language: English
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c5ta01073j

Ru x Ti 1− x Nb 2 O 7 ( x = 0 and 0.01) materials have been synthesized via a solid-state reaction method. X-ray diffraction combined with Rietveld refinements demonstrates that both samples have a Wadsley-Roth shear structure with a C 2/ m space group without any impurities, and that the unit cell volume increases after the trace Ru 4+ doping. Scanning electron microscopy and specific surface area tests reveal that the Ru 4+ doping decreases the average particle size. The Li + ion diffusion coefficient and electronic conductivity of Ru 0.01 Ti 0.99 Nb 2 O 7 are respectively 64% and at least two orders of magnitude larger than those of the pristine TiNb 2 O 7 . First-principles calculations show that the increased electronic conductivity can result from the formation of impurity bands after the Ru 4+ doping. Ru 0.01 Ti 0.99 Nb 2 O 7 exhibits a large initial discharge capacity of 351 mA h g −1 at 0.1 C between 3.0 and 0.8 V vs. Li/Li + , approaching its theoretical capacity (388 mA h g −1 ). At 5 C, unlike the pristine TiNb 2 O 7 with a small charge capacity of 115 mA h g −1 , Ru 0.01 Ti 0.99 Nb 2 O 7 delivers a large value of 181 mA h g −1 , even exceeding the theoretical capacity of the popular spinel Li 4 Ti 5 O 12 (175 mA h g −1 ). After 100 cycles, Ru 0.01 Ti 0.99 Nb 2 O 7 shows a large capacity retention of 90.1%. These outstanding electrochemical performances can be attributed to its improved Li + ionic and electronic conductivity as well as smaller particle size. Ru 0.01 Ti 0.99 Nb 2 O 7 , with a much larger capacity than Li 4 Ti 5 O 12 , fulfils the requirements of high power and energy density for electric vehicles.