Yonglong Wang

Rechargeable lithium/iodine battery with superior high-rate capability by using iodine–carbon composite as cathode

A rechargeable lithium/iodine battery using commercial organic electrolyte, composed of iodine–conductive carbon black composite as cathode and metallic lithium as anode, is first proposed in this work. The fabricated lithium/iodine battery presents superior high-rate capability and good reversibility based on the contributions from both the capacitive characteristics of conductive carbon black, and the redox capacity of active iodine in the composite.

Electrochemical Reduction Mechanism of Fe(VI) at a Porous Pt Black Electrode

Recently, ferrate(VI) has been widely investigated as a cathode material in alkaline batteries. The cathodic reduction process of the ferrate electrode is very important in understanding the electrochemical mechanism as well as in utilizing ferrate as a battery material. In this work, the direct electrochemical reduction process of K 2 FeO 4 was investigated by linear sweep voltammetry (LSV), with a porous Pt black electrode in a 9 M KOH solution at 25°C. The cathodic reaction process of FeO 2― 4 is controlled by the diffusion process in a potential range from 0.20 to 0.53 V (vs Hg/HgO). Moreover, the totally irreversible cathodic reactions of FeO 2― 4 include a rate-controlling step with an electron-transfer number less than 3. Sampled-current voltammetry was also applied to investigate the reaction processes, and the plot exhibits two limited currents. The first one is a weak one-electron limited current, corresponding to the rate-controlling step analyzed by LSV; the other one is a two-electron current. They are both affected by the diffusion of FeO 2― 4 ions. Therefore, the electrochemical reduction mechanism of FeO 2― 4 in 9 M KOH can be inferred as an overall three-electron process with a one-electron transfer as the rate-controlling step, in which the intermediate state of Fe(V) is generated from ferrate(VI).

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–I2) 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–I2 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, I2–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 I2–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 I2–AG composites exhibit high specific capacity, excellent cyclic performance and high rate performance. In particular, the I2–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 I2–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–I2 batteries a promising alternative energy storage device with both high energy and high power density.

Titanium pyrophosphate hexagonal nanoplates for electrochemical lithium storage

Titanium pyrophosphate hexagonal nanoplates were synthesized via facile hydrothermal reaction followed by a calcination procedure. As new cathode materials for lithium-ion batteries, they demonstrate stable cycle performance and high capacity retention at various current densities.