Encapsulating a high content of iodine into an active graphene substrate as a cathode material for high-rate lithium-iodine batteries

Rechargeable lithium-iodine (Li-I-2) batteries are a promising electrochemical energy storage candidate due to their high energy and power density. However, the high solubility of iodine in electrolytes seriously deteriorates the electrochemical performance of Li-I-2 batteries. In addition, the low iodine content in the cathode impedes the enhancement of energy density. Active graphene (AG) has a large specific surface area, abundant micropores and mesopores, free inter-particle voids and unimpeded ion diffusion channels, making it a promising substrate for loading a high content of iodine. In this study, I-2-AG composites were fabricated through an in situ iodine deposition route. The facile synthesis process can introduce a high content of iodine into the nanopores of AG effectively. The microstructure and morphology of the I-2-AG composites were characterized using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) methods. The results show that iodine is well dispersed in the nanopores of AG. The as-prepared I-2-AG composites exhibit high specific capacity, excellent cyclic performance and high rate performance. In particular, the I-2-AG composite, with a high iodine content of 56 wt%, delivers a high capacity of 218 mA h g(-1) at a 1C rate, and maintains 161 mA h g(-1) after 500 cycles, corresponding to a low capacity fading of only 0.023% per cycle. Especially, the I-2-AG composite exhibits outstanding high-rate performance. Even at 20C, an appreciable discharge capacity of 184 mA h g(-1) can still be obtained. The results indicate that the high content of soluble iodine can be well constrained in the nanopores of AG during charging and discharging processes, making Li-I-2 batteries a promising alternative energy storage device with both high energy and high power density.