A titanium-based metal-organic framework as an ultralong cycle-life anode for PIBs.

We achieved excellent anode performance for PIBs based on a metal-organic framework MIL-125(Ti) for the first time. It can deliver a capacity of 208 mA h g-1 at a rate of 10 mA g-1 and a high capacity retention of 90.2% after 2000 cycles at a high rate of 200 mA g-1 with a high coulombic efficiency. The K+ storage mechanism is investigated by the ex situ XRD and IR techniques and confirms that potassium ions are reversibly inserted into the organic moiety without direct engagement of Ti ions.