Aqueous batteries represent a promising direction in energy storage due to their inherent safety, cost-effectiveness, and environmental friendliness compared to conventional non-aqueous systems. Among the various electrode materials explored for these batteries, graphene has emerged as a particularly compelling candidate. Its unique properties, including high electrical conductivity, large surface area, and mechanical robustness, make it well-suited for use in aqueous electrolytes. This article examines the role of graphene-based electrodes in aqueous batteries, focusing on their stability, corrosion resistance, and performance metrics in water-based systems, with comparisons to organic electrolyte counterparts.
Graphene’s stability in aqueous electrolytes is a critical factor for its successful application in batteries. Unlike organic electrolytes, which often require stringent moisture-free conditions, aqueous systems utilize water as the solvent, presenting challenges related to material degradation. Graphene exhibits excellent chemical stability in water, resisting hydrolysis and maintaining structural integrity over extended cycling. This stability is attributed to its sp²-hybridized carbon network, which is less prone to chemical attack compared to traditional electrode materials. In zinc-ion and sodium-ion aqueous batteries, graphene electrodes demonstrate minimal swelling or delamination, even after hundreds of charge-discharge cycles. Studies have shown that graphene retains over 90% of its initial capacity after 500 cycles in mild acidic or neutral aqueous electrolytes, highlighting its durability.
Corrosion resistance is another key advantage of graphene in aqueous battery systems. Metallic electrodes, such as zinc or aluminum, often suffer from parasitic side reactions like hydrogen evolution or passivation in water-based electrolytes. Graphene’s inert nature mitigates these issues, serving as a protective layer when coated onto metal electrodes or as a standalone conductive matrix. For instance, in zinc-ion batteries, graphene-coated zinc anodes exhibit significantly reduced dendrite formation and corrosion rates compared to bare metal anodes. The impermeability of graphene to ions and molecules further prevents electrolyte penetration that could lead to electrode degradation. This corrosion resistance translates into longer battery lifespans and improved safety.
Performance metrics of graphene electrodes in aqueous batteries reveal several advantages over conventional materials. The high electrical conductivity of graphene, typically exceeding 10⁶ S/m, ensures efficient charge transfer, reducing internal resistance and enabling high-rate capability. Aqueous zinc-ion batteries employing graphene cathodes have demonstrated specific capacities ranging from 250 to 400 mAh/g, with energy densities approaching 300 Wh/kg. Sodium-ion aqueous systems with graphene anodes achieve reversible capacities of around 200 mAh/g, competitive with organic electrolyte-based designs. The open porous structure of graphene facilitates rapid ion diffusion, contributing to power densities exceeding 5 kW/kg in some configurations. These metrics are particularly notable given the lower ionic conductivity of aqueous electrolytes compared to organic solvents.
Comparing graphene electrodes in aqueous and organic electrolytes reveals trade-offs tied to the solvent environment. Organic electrolytes, typically employing lithium salts in carbonate-based solvents, offer wider electrochemical stability windows, enabling higher operating voltages. However, graphene electrodes in organic systems often face challenges such as solvent intercalation and solid-electrolyte interphase (SEI) layer formation, which can impede ion transport and reduce cycling efficiency. In contrast, aqueous electrolytes eliminate SEI-related complications, allowing graphene to operate closer to its theoretical performance limits. The absence of flammable organic solvents also enhances safety, a critical consideration for large-scale applications.
The interfacial behavior of graphene differs markedly between aqueous and organic systems. In water-based electrolytes, graphene’s hydrophilic functional groups, such as hydroxyl or carboxyl moieties, promote uniform wetting and ion accessibility. This contrasts with organic electrolytes, where poor wetting can lead to uneven current distribution and localized degradation. The double-layer capacitance of graphene in aqueous electrolytes is typically higher than in organic systems, contributing to improved charge storage at high rates. However, the narrower voltage window of aqueous electrolytes limits the maximum energy density achievable compared to organic counterparts.
Long-term cycling stability of graphene electrodes in aqueous batteries benefits from the absence of solvent decomposition reactions that plague organic systems. While organic electrolytes gradually degrade, forming resistive SEI layers and gas byproducts, aqueous electrolytes remain relatively stable over time. Graphene’s resilience to electrochemical oxidation in neutral or mildly acidic aqueous media further enhances durability. Accelerated aging tests indicate that graphene-based aqueous cells retain over 80% capacity after 1,000 cycles under realistic operating conditions, outperforming many organic electrolyte systems in cycle life.
Environmental and economic considerations further favor graphene in aqueous batteries. The elimination of toxic or flammable organic solvents reduces disposal challenges and manufacturing costs. Graphene production methods have advanced significantly, with scalable techniques like chemical vapor deposition and liquid-phase exfoliation lowering material costs. When combined with abundant aqueous electrolytes, graphene electrodes enable battery systems that are both high-performing and sustainable.
Future developments in graphene electrode design for aqueous batteries may focus on optimizing surface chemistry and architecture. Functionalization with heteroatoms like nitrogen or sulfur could enhance specific capacity while maintaining stability. Three-dimensional graphene foams or vertically aligned structures could further improve ion transport kinetics. As research progresses, graphene-based aqueous batteries may bridge the performance gap with organic electrolyte systems while offering superior safety and sustainability.
In summary, graphene electrodes present a compelling solution for aqueous battery technologies, combining exceptional stability, corrosion resistance, and performance. Their behavior in water-based electrolytes offers distinct advantages over organic systems, particularly in terms of safety and cycle life. While energy density limitations persist compared to non-aqueous batteries, ongoing advancements in graphene engineering continue to narrow this gap, positioning aqueous graphene-based batteries as a viable option for grid storage, electric vehicles, and portable electronics.