Advanced Zinc–Iodine Batteries with Ultrahigh Capacity and Superior Rate Performance Based on Reduced Graphene Oxide and Water‐in‐Salt Electrolyte

Abstract

Aqueous rechargeable zinc-iodine batteries have received increasing attention in the field of portable electronics due to their high safety, low-cost, and great electrochemical performance. However, the insulated nature of iodine and the unrestricted shuttle effect of soluble triiodide seriously limit the lifespan and Coulombic efficiency (CE) of the batteries. Herein, a highperformance zinc-iodine energy storage system based on the hydrothermal reduced graphene oxide (rGO) and a high concentration zinc chloride waterin-salt electrolyte are promoted. The 3D microporous structures and outstanding electrical conductivity of rGO make it an excellent host for iodine, while the water-in-salt electrolyte effectively suppresses the shuttle effect of triiodide and improves the CE of the system. As a result, an ultra-high I 2 mass loading of 25.33 mg cm −2 (loading ratio of 71.69 wt.%) is realized during the continuous charging/discharging process. The batteries deliver a high capacity of 6.5 mAh cm −2 at 2 mA cm −2 with a much-improved CE of 95% and a prominent rate performance with capacity of 1 mAh cm −2 at 80 mA cm −2 . A stable long-term cycling performance is also achieved with capacity retention of 2 mAh cm −2 after 2000 cycles at 50 mA cm −2 .

Bidirectional manipulation of iodine redox kinetics in aqueous Fe–I2 electrochemistry

“…This suggests that NPC and FeP could work synergistically to enable the nearly full iodine confinement. 39…”

Metal–iodine batteries: achievements, challenges, and future

“…85,86 Especially, with a high concentration of ZnCl 2 electrolyte (5 M KI/20 M ZnCl 2 ), Ji et al achieved an advanced Zn-I 2 battery with 2000 cycles without capacity decline, even under an ultra-high iodine load of 25.33 mg cm À2 . 202 Besides, the complexation between PEG400 and iodine can also inhibit the reaction of iodine with I À to form polyiodide. 203 On the other hand, both solid-state and gel electrolytes exhibit the function of restricting the shuttle effect of iodine species due to the restricted solubility of iodine species in these electrolytes.…”

“…As reported by Ji et al, a Zn-I 2 cell based on a hydrothermally RGO cathode and a highly concentrated ZnCl 2 electrolyte (5 M KI/20 M ZnCl 2 ) was able to achieve 2000 cycles without capacity decline even at an ultra-high iodine load of 25.33 mg cm À2 . 202 Nevertheless, the high cost brought by the highly concentrated electrolytes cannot be ignored. Given this, Yang et al developed a novel electrolyte (i.e., 1 M Zn(CF 3 SO 3 ) 2 + 4 M N-methylacetamide + 0.5 M KI in 20% volume fractions of H 2 O) to circumvent the formation of I 3 À intermediates.…”

“…53,83 Combining a hydrothermal reduced graphene oxide cathode with a high concentration of ZnCl 2 electrolyte (5 M KI/20 M ZnCl 2 ), Li et al also realized 2000 cycles without capacity decline even under an ultra-high iodine load of 25.33 mg cm À2 . 202 These works could contribute significantly to the commercialization of Li/Zn-I 2 batteries. Besides, Li/Zn-I 2 batteries, as an emerging technology, may draw valuable insights and research approaches from the relatively mature research field of metal-sulfur batteries due to their high similarity.…”

Long-Lasting Zinc–Iodine Batteries with Ultrahigh Areal Capacity and Boosted Rate Capability Enabled by Nickel Single-Atom Electrocatalysts

“…Different battery systems, including sodium-ion batteries, potassium-ion batteries, and zinc-ion batteries, have been visited because of their abundant precursors and reduced costs, − but these batteries have lower energy density compared with LIBs. Recently, zinc–iodine (Zn–I 2 ) batteries have garnered significant attention because of their high theoretical capacities of zinc and iodine, utilization of safe aqueous electrolytes, rapid ionic conductivity (1.0 S cm –1 ), abundant iodine resources, and cost-effectiveness. , Furthermore, zinc exhibits swift redox chemistry with iodine in aqueous electrolytes, thereby enabling fast discharging and charging of batteries . Unfortunately, Zn–I 2 batteries are hindered by the low conductivity of iodine, generation of soluble intermediates, and associated serious shuttle effects, akin to lithium–sulfur (Li–S) batteries, which results in unwanted self-discharge behavior and short battery lifespan. , …”