Toward Shuttle-Free Zn-I₂ Battery: Anchoring and Catalyzing Iodine Conversion by High-Density P-Doping Sites in Carbon Host

Zn-iodine (I-2) battery, as a promising energy storage device, especially under high I-2 loading, is harassed by the shuttle effect of the soluble polyiodide intermediates. Herein, the bifunctional role of 2D carbon nanosponge with rich P-dopant (4.2 at%) and large specific surface area (1966 m(2) g(-1)) in anchoring I-2/I-x(-) (x = 1, 3 or 5) and catalyzing their mutual conversion is reported. Both experiment and computational results reveal the transfer of electrons from the P-doped site to iodine species, showing strong interfacial interaction. When being used as a host, it possesses high specific capture capacity for I-2 (3.34 g(iodine) g(-1) or 1.6 mg(iodine) m(-2)) and I-x(-) (6.12 g(triiodide) g(-1) or 3.1 mg(triiodide) m(-2)), which thus effectively suppresses the shuttle effect, supported by in situ UV-vis and Raman spectra. In addition to the strong interfacial interaction that favors iodine conversion, the P-doped sites can also catalyze the conversion of I-5(-) to I-2, which is the rate-determining step. Consequently, Zn-I-2 batteries under a high I-2 content (70 wt%) deliver high specific capacity (220.3 mAh g(-1)), superior Coulombic efficiency (>99%), and low self-discharge rate; moreover, they can also operate steadily at 2 A g(-1) with ignorable capacity decay for 10 000 cycles.