Tin oxides with hollandite structure as anodes for lithium ion batteries

Abstract

Tin oxides, K₂(M,Sn)₈O₁₆ (M = Li, Mg, Fe, or Mn), possessing the hollandite crystal structure have been synthesized and characterized by a variety of techniques, and their electrochemical behavior was studied. The compounds K₂(Li_⅔Sn_22/3)O₁₆ (K-Li), K₂(Mn₂Sn₆)O₁₆ (K-Mn), and K₂(Fe₂Sn₆)O₁₆ (K-Fe) are new phases. Rietveld refinement of the powder X-ray diffraction data showed that these Sn-hollandites exhibit a simple tetragonal structure. X-ray photoelectron spectroscopy on (K-Li) and (K-Mg) confirm formal valencies of the ions in the compounds. Galvanostatic cycling versus Li metal in the voltage range of 0.005-1.0 V at the current density of 60 mA/g showed the first cycle charge capacities of 602, 505, 481, and 418 (± 3) mAh/g for (K-Li), (K-Mg), (K-Fe), and (K-Mn), respectively. These values correspond to 3.7-3.0 mol of recyclable Li/mol of Sn. At the end of 50 cycles, (K-Li) and (K-Fe) performed better and retained 78 and 83% of the initial capacity. The (K-Li) also showed good rate capability. The Coulombic efficiency was > 98% between 10 and 50 cycles in all cases except (K-Mn) with the average charge and discharge voltages of 0.4-0.5 and 0.25-0.3 V, respectively. Cyclic voltammograms complement the galvanostatic results. Impedance spectral data on the (K-Li) versus Li at different voltages during the 1st and 15th discharge-charge cycle have been analyzed and interpreted.