Kosmotropic Heparin Sodium Enables Synergistic Solvation Structure Optimization and Interfacial Engineering Toward Highly Reversible Aqueous Zinc‐Ion Batteries

ABSTRACT Conventional electrolyte additives are fundamentally constrained by a trade‐off between bulk solvation regulation and interfacial adsorption stability. Here, we introduce heparin sodium (Hep), a highly sulfonated biopolymer, as a super‐kosmotropic multifunctional additive to synergistically resolve this dilemma. Leveraging its ultrahigh‐density polyanionic clusters (–OSO 3 − and –COO − ) on a rigid polysaccharide backbone, Hep simultaneously restructures the [Zn(H 2 O) 6 ] 2+ solvation sheath and constructs a robust “water‐deficient” inner Helmholtz plane (IHP), suppressing dendrite growth, HER, and corrosive byproduct formation. With the optimized ZSO/0.5 wt.% Hep electrolyte, Zn‖Zn symmetric cells achieve cumulative plated capacities of 2.8, 3.97, and 4.38 Ah at 1, 5, and 10 mA cm − 2 , respectively, and still deliver 0.72 Ah at a high depth of discharge (DOD ≈ 51.3%). Zn‖Cu asymmetric cells maintain an average Coulombic efficiency of 99.58%. Beyond stabilizing the anode, the Hep‐reconstructed solvation sheath enhances Zn 2+ solid‐state diffusion in the V 2 O 5 cathode by ∼1.88‐fold and elevates the surface capacitive contribution ∼3‐fold, enabling a rate capability of ∼120 mAh g − 1 at 4 A g − 1 and an outstanding capacity retention of 90.6% over 2 700 cycles with near‐unity Coulombic efficiency (∼99%). This work establishes a generalizable kosmotropic macromolecular design paradigm for simultaneously engineering anode stability and cathode kinetics in AZIBs.