Persistent and reversible solid iodine electrodeposition in nanoporous carbons

Abstract

Aqueous iodine based electrochemical energy storage is considered a potential candidate to improve sustainability and performance of current battery and supercapacitor technology. It harnesses the redox activity of iodide, iodine, and polyiodide species in the confined geometry of nanoporous carbon electrodes. However, current descriptions of the electrochemical reaction mechanism to interconvert these species are elusive. Here we show that electrochemical oxidation of iodide in nanoporous carbons forms persistent solid iodine deposits. Confinement slows down dissolution into triiodide and pentaiodide, responsible for otherwise significant self-discharge via shuttling. The main tools for these insights are in situ Raman spectroscopy and in situ small and wide-angle X-ray scattering (in situ SAXS/WAXS). In situ Raman confirms the reversible formation of triiodide and pentaiodide. In situ SAXS/WAXS indicates remarkable amounts of solid iodine deposited in the carbon nanopores. Combined with stochastic modeling, in situ SAXS allows quantifying the solid iodine volume fraction and visualizing the iodine structure on 3D lattice models at the sub-nanometer scale. Based on the derived mechanism, we demonstrate strategies for improved iodine pore filling capacity and prevention of self-discharge, applicable to hybrid supercapacitors and batteries.

Iodine Redox Chemistry in Rechargeable Batteries

“…To enable a reversible electrochemical reaction at high current rates, the iodine must maintain intimate contact with an electrically conductive additive. Thus, the loading of iodine into the microporous conductive carbon black (CCB) is necessary to combine the redox capacity contribution of the active iodine with the capacitive characteristics of the CCB substrate [21] . The electrochemical reaction process of active iodine or LiI can be constrained inside the pores of the CCB substrate by strong absorption, thereby leading to good cycling stability.…”

“…Data adapted from Refs. [21, 22f,i–l,n,o,q,r,u, ac,ad,af, 25, 38, 39,48, 50].…”

Iodine Redox Chemistry in Rechargeable Batteries

“…Thus,t he loading of iodine into the microporous conductive carbon black (CCB) is necessary to combine the redox capacity contribution of the active iodine with the capacitive characteristics of the CCB substrate. [21] Thee lectrochemical reaction process of active iodine or LiI can be constrained inside the pores of the CCB substrate by strong absorption, thereby leading to good cycling stability.T he superior highrate capability and large energy density was attributed to the combined contributions of the capacitive characteristic of the CCB substrate and the redox capacity of active iodine in the composite (Figure 7). Theaverage energy density and power density of the composite were up to 91.4 Wh kg À1 and 11.9 kW kg À1 ,respectively,with an average discharge voltage of 2.9 V, based on the total weight of the cathode.…”

“…[3] To eliminate the additional reservoir and pump, static batteries can also be developed by coupling with various metal anodes.U ndesirable reactions and changes commonly result in as erious capacity decay and severe self-discharge owing to shuttling effects.T oa ddress the above issues,m any studies have been carried out to increase the binding force between the electrode and active materials.F or example, ac omposite cathode was prepared by mixing conductive carbon black and iodine,w hereby the soluble I 2 or LiI was firmly fixed thanks to the confinement effect of the highly porous structure. [21] Continuous progress has been made with iodine-based batteries (Figure 1), and this Minireview summarizes recent advances in the design strategies for advanced cathodes as well as cell design aspects,w ith an in-depth fundamental understanding of the redox chemistry of iodine and polysulfide for improving the energy density and cycling stability.F uture research directions and the technical challenges of iodine-based batteries are also addressed. It is imperative and important to update the significant progress made in the development of rechargeable iodine-based batteries in combination with advanced electrodes and novel cell configurations.…”

Low-Temperature Synthesis of Monolithic Titanium Carbide/Carbon Composite Aerogel

“…By comparison with the pseudomorphic transformation method, the solid-state reaction is relatively easy to control and scale up. Carbon aerogel is an excellent template because of its low density and high porosity [ 36 , 37 , 38 , 39 , 40 , 41 ], so it was a good choice for us to increase the strength of the framework structure. Thus, in this paper, we tried to apply the simple low-temperature magnesiothermic conversion method to synthesize titanium carbide in the TiO 2 /C composite aerogel to maintain its nanoporous microstructure and overcome the disadvantage of high temperature and high energy consumption in the preparation process.…”