High-Performance Electrochemical Capacitors with Aqueous Electrolytes

Electrochemical capacitors, often termed supercapacitors, are emerging as vital components in modern energy-storage systems due to their ability to deliver high power density, rapid charge–discharge cycles and long operational lifetimes. The use of aqueous electrolytes confers inherent safety, low cost and environmental friendliness, yet has traditionally been limited by the narrow electrochemical stability window of water. Recent advances have sought to overcome this constraint through electrolyte engineering—such as highly concentrated “water-in-salt” formulations and deep eutectic solvents—as well as electrode surface modifications to suppress corrosion and gas evolution. These innovations have extended cell voltages beyond 2.5 V, elevated energy densities to rival those of organic systems, and demonstrated stable cycling over tens of thousands of cycles. Collectively, these developments point towards practical, scalable aqueous devices for grid stabilisation, electric vehicles and portable electronics, marrying high performance with safety and sustainability.

Research from Nature Portfolio

Innovative large-scale production methods have highlighted the practical viability of aqueous systems. A recent study demonstrated a roll-to-roll coating of a hydrophobic graphite layer on aluminium current collectors, suppressing corrosion and oxide formation in cylindrical 18 650 cells. This anti-corrosion passivation maintained intimate contact with activated carbon electrodes, yielding excellent rate capability and zero capacitance loss over extended cycling, a pivotal step towards commercial aqueous supercapacitors. Foundational work on saturated sodium perchlorate solutions revealed an unprecedented electrochemical stability window of approximately 3.2 V in water. By integrating these highly concentrated electrolytes into asymmetric carbon–metal oxide cells, energy densities in excess of 36 Wh kg−1 were achieved without gas evolution, underscoring the historic significance of electrolyte composition in transcending conventional aqueous voltage limits.

High-Performance Electrochemical Capacitors with Aqueous Electrolytes publication trend

The graph below shows the total number of articles in high-performance electrochemical capacitors with aqueous electrolytes across all publications each year (not limited to Nature Index journals).

Technical terms

Aqueous electrolyte: A water-based ionic medium for charge transport, valued for safety and conductivity but limited by water’s decomposition voltage.

Water-in-salt electrolyte: A highly concentrated aqueous salt solution in which water molecules are outnumbered by ions, widening the electrochemical stability window by suppressing water splitting.

Deep eutectic solvent (DES): A mixture of hydrogen-bond acceptors and donors that forms a low-melting, ionic liquid–like medium, offering low volatility and expanded voltage windows in supercapacitors.

Electrochemical stability window: The voltage range over which an electrolyte remains inert, beyond which decomposition or gas evolution occurs.

Electrical double-layer capacitance (EDLC): Charge storage arising from ion adsorption at the electrode–electrolyte interface, characterised by fast kinetics and high power density.

Pseudocapacitance: Faradaic charge storage involving reversible redox reactions at or near the electrode surface, contributing additional capacitance beyond the double layer.

References

1. Sodium Nitrate/Formamide Deep Eutectic Solvent as Flame‐Retardant and Anticorrosive Electrolyte Enabling 2.6 V Safe Supercapacitors with Long Cyclic Stability. Energy & Environmental Materials (2023).
2. An aqueous electrolyte of the widest potential window and its superior capability for capacitors. Scientific Reports (2017).
3. Scalable 18,650 aqueous-based supercapacitors using hydrophobicity concept of anti-corrosion graphite passivation layer. Scientific Reports (2021).
4. Effect of conductivity, viscosity, and density of water-in-salt electrolytes on the electrochemical behavior of supercapacitors: molecular dynamics simulations and in situ characterization studies. Materials Advances (2022).