Deploying Cationic Cellulose Nanofiber Confinement to Enable High Iodine Loadings Towards High Energy and High-Temperature Zn-I2 Battery.

High iodine loading and high-temperature adaptability of the iodine cathode are prerequisites to achieving high energy density at full battery level and promoting the practical application for the zinc-iodine (Zn-I2 ) battery. However, it would aggravate the polyiodide shuttle effect when employing high iodine loading and working temperature. Here, a sustainable cationic cellulose nanofiber (cCNF) was employed to confine the active iodine species through strong physiochemical adsorption to enlarge the iodine loading and stabilize it even at high temperatures. The cCNF could accommodate dual-functionality by enlarging the iodine loading and suppressing the polyiodide shuttle effect, owing to the unique framework structure with abundant surface positive charges. As a result, the iodine cathode based on the cCNF could deliver high iodine mass loading of 14.1 mg cm-2 with a specific capacity of 182.7 mAh g-1 , high areal capacity of 2.6 mAh cm-2 , and stable cycling over 3000 cycles at 2 A g-1 , thus enabling a high energy density of 34.8 Wh kg-1 and the maximum power density of 521.2 W kg-1 at a full Zn-I2 battery level. In addition, even at a high temperature of 60 °C, the Zn-I2 battery could still deliver a stable cycling.

Initiating a composite membrane with a localized high iodine concentration layer based on adduct chemistry to enable highly reversible zinc-iodine flow batteries.

The issue of polyiodide crossover at an iodine cathode significantly diminishes the efficiency and practicality of aqueous zinc-iodine flow batteries (ZIFBs). To address this challenge, we have introduced a localized high iodine concentration (LHIC) coating layer onto a porous polyolefin membrane, which featured strong chemical adsorption by exploiting adduct chemistry between the iodine species and a series of low-cost oxides, e.g., MgO, CeO2, ZrO2, TiO2, and Al2O3. Leveraging the LHIC based on the potent iodine adsorption capability, the as-fabricated MgO-LHIC composite membrane effectively mitigates iodine crossover via Donnan repulsion and concentration gradient effects. At a high volumetric capacity of 17.8 Ah L-1, ZIFBs utilizing a MgO-LHIC composite membrane exhibited improved coulombic efficiency (CE) and energy efficiency (EE) of 96.3% and 68.6%, respectively, along with long-term cycling stability of 170 cycles. These results significantly outperform those of ZIFBs based on a blank polyolefin membrane (78.2%/61.9% after 60 cycles) and the widely used commercial Nafion N117 (67.8%/53.0% after 23 cycles). Even under high-temperature conditions (60 °C), the LHIC-based battery still demonstrates superior CE/EE of 95.1%/67.5% compared to those of the blank polyolefin membrane (CE/EE: 61.1%/46.8%). Our pioneering research showcases enormous prospects for developing high-efficiency and low-cost composite membranes based on adduct chemistry for large-scale energy storage applications.