Nanostructured TiO2 as anode material for potassium batteries

The development of solar energy conversion technologies energy must be coupled with efficient storage systems or solar fuels generators (like NH3). Nowadays, the most known batteries are lithium-ion ones (LIBs), that allowed the great success of portable electronic devices in the last decade. However, the low natural abundance of lithium threatens the further development of LIBs; consequently, the research moved toward post-lithium batteries, such as potassium-ion systems (PIBs). Due to the large atomic radius of potassium, some electrode materials that are commonly used in Li‐ion systems are not suitable for potassium batteries. Thus, anode and cathode materials that can tolerate the intercalation/deintercalation of K+, without suffering from the reorganization energy, are needed. Herein, we report the use of TiO2, in the form of both nanoparticles (NP) and nanotubes (NT), as anode material for PIBs. TiO2 NPs afforded a quite stable specific capacity, with a 87.4% retention efficiency after 200 charge/discharge cycles, when KFSI in DME was used as electrolyte. The Coulombic efficiency (CE) was remarkably high (> 98%), starting from the first cycles, suggesting the high reversibility of the insertion reaction. TiO2 NTs were synthesized by anodic oxidation of a Ti foil, in both the amorphous and the anatase phase and by varying the anodization time. In the best case, the specific capacity was 75 µAh/cm2, with a retention efficiency of 86.4% after 200 cycles and a CE of 98%. This preliminary work paves the way to a further development of nanostructured TiO2 as anode material in the PIB field.