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Niobium-substituted hollandite-type titanium dioxides with different potassium content in the tunnel space, KxTi1–yNbyO2, were synthesized by potassium extraction method using H2SO4/H2O2 solution. Rietveld refinement from X-ray powder diffraction data of the most potassium-extracted specimen, K0.06Ti0.9Nb0.1O2, showed it to have the hollandite-type structure (tetragonal; space group I4/m; a = 10.26725(11) A and c = 2.98759(5) A; Z = 8). Both KxTi0.9Nb0.1O2 (x = 0.19 and 0.06) specimens worked as rechargeable electrode materials for lithium batteries in the voltage range of 1.0 V to 3.0 V, and the initial lithium insertion capacity significantly increased from 15 mAh g−1 to 130 mAh g−1 with decreasing of potassium content. The small amount of residual K+ ions in the tunnel space affected the initial charge–discharge efficiency and the cyclability of the KxTi1-yNbyO2 electrodes. Cyclic voltammograms of the K0.06Ti0.9Nb0.1O2 electrode showed three pairs of redox peaks, and X-ray absorption spectra of the electrodes after charge-discharge measurements elucidated that both Ti and Nb contributed to the redox reaction. |
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