Zn-ion ultrafluidity by coupling ion-sieving and Zn ion replenishment for highly reversible Zn-metal anode chemistry

The commercialization of aqueous zinc-ion batteries (AZIBs) is hindered by the poor reversibility of Zn-metal anodes, which suffer from dendrite growth, hydrogen evolution reaction (HER), and corrosion. This work designs a gradient organic-inorganic (GOI4) protective layer on the Zn anode, which is composed of a Zn-rich inorganic montmorillonite (Zn-MMT) sub-layer and an organic hydroxypropyl guar gum (HGG) top-layer. The -OH of HHG acts as valve for gating Zn²⁺ ‘on’ and anions ‘off’ states to block water and SO₄^2-, while close-fitting Zn-rich MMT at interface can provide rapid interfacial Zn²⁺ replenishment to homogenize ion flux and its feasible mechanical strength promises suppression of dentrites formation. Through theoretical calculation, the lower transfer energy barrier of Zn²⁺ in GOI4 layer provides unique benefits to accelerating fast Zn migration, decreasing the concentration polarization. Consequently, the GOI4@Zn symmetric cell achieves exceptional cycling stability over 2700 hours at 0.25 mA cm^-2/0.25 mA cm^-2 and operates reliably even at ultrahigh current density (5 mA cm^-2, 1 mAh cm^-2 for 4000 h). When paired with I₂@PAC cathode, the full cell also demonstrates long-term cycling (e.g., 20,000 cycles with 87.5% capacity retention). This work provides a feasible strategy for developing highly reversible Zn anodes for practical AZIBs.