Aromatic Organic Small-Molecule Material with (020) Crystal Plane Activation for Wide-Temperature and 68000 Cycle Aqueous Calcium-Ion Batteries.

Calcium-ion batteries are an emerging energy storage device owing to the low redox potential of Ca/Ca and the naturally abundant reserves of the Ca element. However, the high charge density and large radius of Ca lead to a low calcium storage capacity or unsatisfactory cycling performance for most electrode materials. Herein, we report the organic crystal 3,4,9,10-perylenetetracarboxylic diimide (PTCDI) as an anode material for aqueous calcium-ion batteries (ACIBs) in a water-in-salt electrolyte. PTCDI delivers a high discharge capacity of 131.8 mAh g, excellent rate performance (86.2 mAh g@10000 mA g), and an ultralong life of 68000 cycles (over 470 days) with a high capacity retention of 72.7%. The calcium storage mechanism of PTCDI is shown to be an enolization reaction by attenuated total reflectance Fourier-transform infrared and X-ray photoelectron spectroscopy. The activation mechanism of PTCDI microribbon splitting along the (020) crystal plane is studied by X-ray diffraction, 3D tomography reconstruction technologies, and transmission electron microscopy. In addition, the Ca storage sites and diffusion pathways of PTCDI are studied by density functional theory calculations. Finally, by matching a high-voltage Prussian blue analogue cathode, the assembled aqueous calcium-ion full cells exhibit excellent wide-temperature operating capability (-20 to +50 °C) and an ultralong life of 30000 cycles. Further, an aqueous calcium-ion pouch cell is constructed and exhibits a long lifetime of over 500 cycles.