Zinc anodes have long been considered promising candidates for energy storage systems due to their high theoretical capacity, low cost, and environmental friendliness. However, their practical implementation faces several challenges, including dendrite formation, passivation, and shape change. These issues significantly impact the coulombic efficiency and cycling stability of zinc-based batteries, limiting their commercial viability.

Dendrite formation is one of the most critical problems affecting zinc anodes. During repeated charge-discharge cycles, uneven zinc deposition leads to the growth of needle-like dendrites, which can penetrate separators and cause internal short circuits. This phenomenon is exacerbated by high current densities and non-uniform ion flux distribution. Dendrite growth not only reduces battery lifespan but also poses safety risks.

Passivation occurs when zinc reacts with the electrolyte to form insulating layers, such as zinc oxide or zinc hydroxide, on the anode surface. These layers increase interfacial resistance and hinder ion transport, leading to voltage polarization and capacity fading. In alkaline electrolytes, passivation is particularly severe due to the high solubility of zinc species, which promotes the formation of dense, non-conductive films.

Shape change refers to the redistribution of active material across the electrode surface during cycling, resulting in thickness variations and loss of electrical contact. This issue arises from the dissolution and redeposition of zinc in regions with higher current density, causing electrode deformation over time. Shape change reduces the effective surface area and contributes to capacity degradation.

To mitigate dendrite formation, researchers have explored alloying additives such as bismuth (Bi) and indium (In). These elements modify the zinc deposition behavior by increasing nucleation sites and promoting uniform plating. Bismuth, for example, forms a solid solution with zinc, reducing the overpotential for deposition and suppressing dendritic growth. Indium improves the reversibility of zinc stripping and plating by enhancing surface wetting and reducing hydrogen evolution.

Another approach involves designing 3D porous structures for zinc anodes. These architectures provide a large surface area, lower local current density, and improved ion diffusion, which collectively suppress dendrite formation. Porous zinc foams, carbon-based scaffolds, and conductive polymer matrices have demonstrated enhanced cycling stability by facilitating homogeneous zinc deposition and accommodating volume changes.

Electrolyte modifications play a crucial role in addressing passivation and improving coulombic efficiency. Additives such as polyethylene glycol (PEG) and sodium dodecyl sulfate (SDS) adsorb onto the zinc surface, forming protective layers that inhibit side reactions and promote smooth deposition. pH control is also critical, as excessively alkaline or acidic conditions accelerate corrosion and passivation. Neutral or mildly acidic electrolytes are often preferred to balance stability and performance.

Coulombic efficiency, defined as the ratio of discharge capacity to charge capacity, is a key metric for evaluating zinc anode performance. High coulombic efficiency indicates minimal side reactions, such as hydrogen evolution or zinc corrosion. Strategies like electrolyte optimization and interfacial engineering have achieved efficiencies exceeding 99% in controlled conditions, though practical systems still face challenges in maintaining this over extended cycling.

Cycling stability remains a major hurdle for zinc anodes, with many systems experiencing rapid capacity fade after a few hundred cycles. The interplay between dendrite suppression, passivation resistance, and shape change mitigation determines long-term performance. Advanced characterization techniques, such as in-situ microscopy and electrochemical impedance spectroscopy, provide insights into degradation mechanisms and guide material design.

Despite these challenges, recent advancements in zinc anode engineering show promise for overcoming existing limitations. The combination of alloying additives, 3D architectures, and tailored electrolytes offers a pathway toward stable, high-performance zinc-based batteries. Continued research into interfacial dynamics and degradation mechanisms will be essential for unlocking the full potential of this technology.

In summary, zinc anodes face significant obstacles related to dendrite formation, passivation, and shape change, which impact their efficiency and durability. Mitigation strategies involving alloying, structural design, and electrolyte modifications have shown encouraging results, but further optimization is needed to achieve commercial-scale adoption. The development of robust zinc anodes could enable next-generation energy storage systems with improved sustainability and cost-effectiveness.