Pretreated commercial TiSe2 as an insertion-type potassium container for constructing “Rocking-Chair” type potassium ion batteries

Potassium ion batteries have suffered from a severe lack of proper insertion-type electrodes since the large-sized potassium ion cannot be accommodated in most of lithium/sodium ions anode materials. Here, we report commercial TiSe2 as a novel potassium insertion material. The electrochemical results show that commercial TiSe2 can electrochemically store the potassium ions reversibly with good cyclability and excellent rate performance. However, it is plagued by the low Coulombic efficiency in the first cycle. Upon investigation of in situ X-ray diffraction, its irreversible capacity loss is caused by the cracks of the TiSe2 host along with phase transitions. We design an efficient method to eliminate its irreversible capacity loss and then couple the as-pretreated TiSe2 with the as-pretreated Prussian blue for fabrication of full cell. The Coulombic efficiency of this full cell is improved and this full cell displays stable cyclability with good capacity retention of 94.5 % after 120 cycles.