Physicochemical Confinement Effect Enables High-Performing Zinc–Iodine Batteries

Abstract

Zinc–iodine batteries are promising energy storage devices with the unique features of aqueous electrolytes and safer zinc. However, their performances are still limited by the polyiodide shuttle and the unclear redox mechanism of iodine species. Herein, a single iron atom was embedded in porous carbon with the atomic bridging structure of metal–nitrogen–carbon to not only enhance the confinement effect but also invoke the electrocatalytic redox conversion of iodine, thereby enabling the large capacity and good cycling stability of the zinc–iodine battery. In addition to the physical trapping effect of porous carbon with good electronic conductivity, the in situ experimental characterization and theoretical calculation reveal that the metal–nitrogen–carbon bridging structure modulates the electronic properties of carbon and adjusts the intrinsic activity for the reversible conversion of iodine via the thermodynamically favorable pathway. This work demonstrates that the physicochemical confinement effect can be invoked by the rational anchoring of a single metal atom with nitrogen in a porous carbon matrix to enhance the electrocatalytic redox conversion of iodine, which is crucial to fabricating high-performing zinc–iodine batteries and beyond by applying the fundamental principles.

High-Performance Zn–I2 Batteries Enabled by a Metal-Free Defect-Rich Carbon Cathode Catalyst

“…Although the overpotential change for the reduction process is smaller than that for the oxidation process (Figure 3d), the DG1100/I 2 -based battery showed a smaller gap between the reduction peak potential and oxidation peak potential than that of the NG800/I 2 -based battery (Figure 3c,d), indicating that the DG1100/I 2 electrode has smaller polarization and better reversibility. 20 Additionally, the DG1100/I 2 battery illustrated higher positive and negative current densities of 1.62 and 1.26 mA cm −2 , respectively (Figure 3e), suggesting the high IRR catalytic activity of DG11000 in Zn−I 2 batteries. More importantly, the DG1100/ I 2 electrode possessed a lower Tafel slope of 81.2 mV•dec −1 than that of the NG800/I 2 electrode (124.2 mV•dec −1 ) (Figure 3f), indicative of faster reaction dynamics in Zn−I 2 batteries.…”

“…However, due to the electrochemically inactive properties of these carbons, their capacity and the reaction kinetics of I 2 conversion were limited. To overcome these limitations, heteroatom-doped porous carbon materials were 20 The porous structure has given physical space for the confined adsorption of iodine species, while the Fe−N 4 −C moiety in B−Fe−NC strengthened the chemical trapping for I 2 species and boosted the electrocatalytic redox conversions, offering a physicochemical confinement effect for rationally designed advanced electrode materials for Zn−I 2 batteries. As inspired by their interesting work, we prospect that defect-rich carbon nanomaterials may be an efficient catalyst cathode for the I 2 conversion reaction and the corresponding Zn−I 2 batteries because defect-induced active sites are widely reported in various catalytic reactions and related energy devices.…”

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

“…As displayed in Figure 3f, the open-circuit voltage for the NiSAs-HPC/I 2 cathode delivered ultrahigh stability for ∼100 h with higher voltages, thereby suggesting that polyiodide dissolution and shuttling can be well suppressed. 23 The Zn−I 2 batteries using the NiSAs-HPC/I 2 cathode exhibited a highly stable cyclic performance with enhanced specific capacities at 5.0 C (Figure 3g) compared with those of Zn−I 2 batteries using the HPC/I 2 cathode. Specifically, the batteries using the NiSAs-HPC/I 2 cathode delivered a high initial specific capacity of 188 mAh g −1 and maintained steadily for 1000 cycles with a high specific capacity of 179 mAh g −1 , which corresponded to a remarkable capacity retention of 95.2%.…”

“…Notably, the galvanostatic discharge/charge profiles of Zn–I 2 batteries using NiSAs-HPC/I 2 cathode possessed a lower potential polarization (38 mV) compared with that of the Zn–I 2 batteries using a HPC/I 2 cathode (61 mV). , The self-discharge behaviors of Zn–I 2 batteries using NiSAs-HPC/I 2 and HPC/I 2 cathodes were also investigated. As displayed in Figure f, the open-circuit voltage for the NiSAs-HPC/I 2 cathode delivered ultrahigh stability for ∼100 h with higher voltages, thereby suggesting that polyiodide dissolution and shuttling can be well suppressed …”

“…Doping heteroatoms (e.g., nitrogen, phosphorus, sulfur) within carbonaceous materials can alleviate the aforementioned issues to a large extent by regulating the surface charge environments of adjacent carbon atoms. ,, Nevertheless, the resulting electrochemical performances are still far from satisfactory, and thus, substantial efforts must be made. Recently, it has been recognized that the chemical confinement of polyiodides can improve battery performance because the polar species can adsorb polyiodides and catalyze their conversion simultaneously. − For instance, Zhi et al reported a MXene-based host to restrict polyiodides and promote their mutual conversions through strong chemical adsorption and excellent catalytic effects . The resultant Zn–I 2 batteries exhibited a high rate capability (143 mAh g –1 at 18 A g –1 ) and long lifespan (∼23 000 cycles).…”