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(Li2/3Sn22/3)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 Co...