In situ preparation of CuCl cubic particles on the commercial copper foil: its significant facilitation to the electrochemical performance of the commercial graphite and its unexpected photochromic behavior

An immersion method employing the commercial copper foil, CuSO4 solution and an ionic liquid of 1-butyl-3-methylimidazole chloride as the starting materials for preparing cuprous chloride (CuCl) on the surface of commercial copper foil (denoted as CuCl/Cu) at room temperature is developed in this work for the first time. As verified by the SEM images, a large number of cubic particles are prepared on the surface of the commercial copper foil after a simple immersion process, and XRD and XPS analysis substantially indicate that these synthesized cubic particles are CuCl particles. Interestingly, the initial discharge capacity of the commercial graphite at 0.1A g(-1) is increased from 263 mAh g(-1) on the commercial copper foil to 681 mAh g(-1) on CuCl/Cu. And even at 1.0 A g(-1) after 100 cycles, the discharge capacity of the graphite on CuCl/Cu is 128 mAh g(-1), still 3.7 times larger than that on the Cu foil (34 mAh g(-1)). Incredibly, the color of CuCl cubic particles can vary from coppery color to black when it is illuminated by a light source for 30 min, suggesting that the as-prepared CuCl cubic particles are a kind of photochromic materials, showing a potential application in the field of military stealth materials. (C) 2020 Elsevier B.V. All rights reserved.