Lithium insertion and extraction properties of hollandite-type KxTiO2 with different K content in the tunnel space

Abstract Three hollandite-type K x TiO 2 specimens with different K content in the tunnel space were prepared by the K + ions extraction using HCl and HNO 3 /HCl solutions. The K x TiO 2 specimens worked as rechargeable electrode materials in the voltage range of 1.0 V to 3.0 V, and the initial Li insertion capacities increased from 63 mAh g − 1 to 158 mAh g − 1 with decreasing of K + ions. Neutron powder diffraction investigation elucidated that the tunnel space of K 0.008 TiO 2 with lowest K content was essentially empty, and no water species such as H 2 O and H 3 O + were detected by the nuclear scattering length density distribution calculated by the maximum entropy method based on the Rietveld analysis using neutron powder diffraction data. The K 0.008 TiO 2 specimen showed good cycling and rate performances. The rechargeable capacity at 0.1 C was about 150 mAh g − 1 with a capacity retention rate of 97% over 2–50 cycles, and even at the high rate of 10 C, the capacity exceeded 100 mAh g − 1 . The empty tunnel in the hollandite-type TiO 2 is promising as the storage space for Li + ions.