K₂Ti₆O₁₃/carbon core-shell nanorods as a superior anode material for high-rate potassium-ion batteries

Bunches of oriented K2Ti6O13 nanorods coated by a thin carbon layer (4-7 nm) were prepared by combining hydrothermal and heat treatment in sequence. The K2Ti6O13 nanorods possess long- and short-axis crystal orientations of <010> and <001>, respectively, contributing to fast K+ diffusion, and the carbon-coating layer improves the electron conductivity. In addition, the obtained K2Ti6O13/carbon has a high compaction density, which is beneficial for realizing high volumetric specific capacity. When evaluated as a potassium-ion battery anode, the nanorods demonstrated a superior rate capability (122.5, 104.3, 92.3, 78.6 and 65.1 mA h g-1 at current densities of 20, 50, 100, 200 and 500 mA g-1, respectively), a favourable cycle life (118.5 mA h g-1 at 25 mA g-1 for 200 cycles) and high capacity retention.