Two‐Electron Redox Chemistry Enabled High‐Performance Iodide‐Ion Conversion Battery

Abstract

A single‐electron transfer mode coupled with the shuttle behavior of organic iodine batteries results in insufficient capacity, a low redox potential, and poor cycle durability. Sluggish kinetics are well known in conventional lithium–iodine (Li−I) batteries, inferior to other conversion congeners. Herein, we demonstrate new two‐electron redox chemistry of I−/I+ with inter‐halogen cooperation based on a developed haloid cathode. The new iodide‐ion conversion battery exhibits a state‐of‐art capacity of 408 mAh gI−1 with fast redox kinetics and superior cycle stability. Equipped with a newly emerged 3.42 V discharge voltage plateau, a recorded high energy density of 1324 Wh kgI−1 is achieved. Such robust redox chemistry is temperature‐insensitive and operates efficiently at −30 °C. With systematic theoretical calculations and experimental characterizations, the formation of Cl−I+ species and their functions are clarified.

Development of long lifespan high-energy aqueous organic||iodine rechargeable batteries

“…For anions, the lowest dissociation energy of ICl was observed when compared to that of other iodine compounds, indicating the fast conversion of I 0 /I + in aqueous electrolyte containing Cl − (Fig. 1b ) 2 , 3 , 5 . Accordingly, the aqueous KCl electrolyte should guarantee the highly reversible redox reaction of the I 2 cathode.…”

“…As a result, the discharge cell voltage could be promoted due to the reduced polarization 5 . For the I 0 /I + conversion, the anion in the selected electrolyte must facilitate the dissociation of I + compounds to accelerate the I 0 /I + conversion 2 , 3 , 5 . Regarding the anode, only when it simultaneously satisfies the demands of structural stability, inertness to various iodine anionic species, low redox potential, high capacity and low cost can it guarantee a long lifespan with an improved energy outcome.…”

“…During the charge/discharge process, the oxidation/reduction reaction of I − /I 0 /I + occurred at the I 2 @AC electrode, and the enolization/recovery of carbonyl groups occurred at the PTCDI electrode with K + intercalation/deintercalation (Supplementary Fig. 8a, b ) 2 , 3 , 5 . Hence, the chemical equations of the PTCDI||I 2 glass cell in a saturated KCl aqueous electrolyte can be described as Eqs.…”

“…Oxidation peaks at 1.54 V, 2.24 V and reduction peaks of 1.71 V, 0.91 V, 0.72 V were clearly observed. For the I 2 @AC electrode, the redox pair of 2.24 V/1.71 V corresponds to the reversible reaction of I 0 /I + while the remaining redox pairs correspond to the reversible transformation between I − and I 0 2 , 3 , 5 . For the PTCDI electrode, the anodic and cathodic peaks correspond to the stepwise intercalation and deintercalation of K + 34 , 41 , 43 .…”

“…Moreover, a discharge capacity of 364 mAh g −1 was delivered after the initial activation process. Such a high discharge capacity originated from the full use of I − /I 0 /I + conversion reactions 2 , 3 , 5 . A discharge capacity of 156 mAh g −1 was achieved after 92,000 cycles at 40 A g −1 (Fig.…”