Moderately hydrophobic polymer protective layer enables Zn (100) deposition for high utilization zinc anodes

Rechargeable aqueous zinc-ion batteries (AZIBs) hold immense promise for large-scale energy storage owing to zinc's natural abundance, intrinsic safety, and high theoretical capacity (820 mAh g^-1). Yet conventional AZIBs suffer from a critical paradox: excessive Zn loading is required to compensate for irreversible losses during stripping/plating, which accelerates electrolyte depletion, lowers Zn utilization, and severely degrades energy density. The root cause lies in the dual challenges of uncontrolled dendrite growth and parasitic hydrogen evolution reaction (HER) at the Zn anode surface. Existing polymer protective layers—while mechanically adaptable—typically rely on hydrophilic groups that form strong hydrogen bond (HB) networks with interfacial H₂O. These networks inadvertently promote H⁺ transport via the "Grotthuss" mechanism, accelerating HER and limiting both cycling stability and Zn utilization. Conversely, excessively hydrophobic layers block water contact but hinder Zn²⁺ desolvation and transport, imposing high charge-transfer resistance. Now, researchers led by Peiyi Wu and Yucong Jiao at Donghua University have engineered a breakthrough polymer protective layer (PDMAG@Zn) that resolves this hydrophilicity–hydrophobicity dilemma through precisely balanced interfacial engineering.

Innovative Design and Mechanism

The PDMAG layer is constructed via in situ polymerization of poly(N,N-dimethylacrylamide) (PDMAA) and cationic guar gum (CGG) on the Zn surface. The steric hindrance of PDMAA's dual –CH₃ substituents endows the layer with moderate hydrophobicity—a critical design parameter that fundamentally reconfigures interfacial water behavior. Unlike conventional hydrophilic polymers (e.g., PAM) that form continuous HB networks facilitating proton transport, PDMAG blocks the Grotthuss effect by disrupting the HB network of bulk electrolyte water and confining H₂O activity through weak HB interactions between –C=O groups and H₂O molecules. This molecular architecture effectively suppresses HER while maintaining sufficient polymer chain mobility to facilitate Zn²⁺ transport via a molecular lubrication mechanism.

Simultaneously, the electronegative –C=O groups in PDMAA exhibit stronger coordination with Zn²⁺ (binding energy: −2.45 eV vs. −1.91 eV for PAM), enabling preferential adsorption on the Zn (100) crystal plane. DFT calculations confirm that PDMAA adsorption energy on Zn (100) (−1.205 eV) is significantly lower than on Zn (101) and Zn (002), thermodynamically favoring oriented deposition. The Zn (100) plane—with its intrinsically low surface diffusion barrier and fastest growth kinetics—forms vertically aligned, thick, and highly ordered facets that minimize aspect ratio, suppress internal short circuits, and deliver the highest critical areal capacity. This crystallographic guidance, combined with CGG-induced interfacial stabilization, establishes a robust solid-electrolyte interphase that ensures uniform Zn²⁺ flux distribution and dendrite-free deposition.

Outstanding Performance

The PDMAG@Zn anode delivers exceptional electrochemical metrics across multiple dimensions. The symmetrical battery achieves ultralong cycling of 6,580 hours (>9 months) at 1 mA cm^-2, 1 mAh cm^-2, and sustains 300 hours at 1 mA cm^-2, 15 mAh cm^-2 with an unprecedented 91.5% depth of discharge (DOD)—among the highest reported Zn utilization rates. At 5 mA cm^-2, 5 mAh cm^-2 (30.5% DOD), the system operates stably for over 1,200 hours. The Coulombic efficiency reaches 98.6% in reservoir-based Zn||Cu testing, with a corrosion rate of merely 3.5 μg h^-1 (vs. 12 μg h^-1 for bare Zn).

Kinetic isotope effect (KIE) experiments provide direct mechanistic validation: PDMAG@Zn exhibits a KIE value of 1.1 (vs. 2.9 for bare Zn and 2.3 for PACG@Zn), confirming minimal proton involvement in interfacial HER. In situ electrochemical gas chromatography demonstrates nearly undetectable H₂ evolution during 120-minute plating at 10 mA cm^-2, while the electrochemical stability window expands to 2.72 V—the broadest among tested configurations. The Zn²⁺ transference number reaches 0.81, reflecting facilitated desolvation with an activation energy of only 26.2 kJ mol^-1 (vs. 48.6 kJ mol^-1 for bare Zn).

When paired with a V₂O₅ cathode, the full battery delivers a high capacity of 335 mAh g^-1 at 1 A g^-1 with 67% capacity retention after 800 cycles. At 5 A g^-1, it maintains 227 mAh g^-1 with 89% retention over 1,500 cycles. Critically, the electronegative PDMAG layer electrostatically repels dissolved vanadate anions (V₂O₇^4-), preventing cathode-derived by-product crossover and anode poisoning—a persistent failure mode in Zn||V₂O₅ systems. A 3 × 3 cm² pouch cell achieves 290.5 mAh g^-1 (28.9 mAh) at 0.5 A g^-1 with 76% retention after 150 cycles at a low N/P ratio of 3.6, underscoring superior practical feasibility.

Applications and Future Outlook

This work establishes a transformative strategy for constructing stable, high-utilization Zn anodes by resolving the long-standing trade-off between HER suppression and ion transport kinetics. The moderately hydrophobic PDMAG architecture—combining water-repelling functionality with zincophilic coordination—opens promising avenues for next-generation aqueous batteries combining high energy density, extended cycle life, and scalable manufacturability. The demonstrated pouch cell performance and deep-cycling capability at 91.5% DOD position this technology as a compelling candidate for grid-scale energy storage and beyond.

Stay tuned for more groundbreaking research from this team at Donghua University!