The integration of lightweight carbon-based nanomaterials as current collectors in energy storage devices represents a significant advancement in battery and supercapacitor technology. Traditional metal foils, such as copper and aluminum, have long served as current collectors due to their high electrical conductivity. However, their weight, susceptibility to corrosion, and limited flexibility pose challenges for next-generation energy storage systems. Carbon nanotube (CNT) and graphene films have emerged as promising alternatives, offering superior conductivity, corrosion resistance, and mechanical robustness while significantly reducing device weight.

Electrical conductivity is a critical parameter for current collectors, as it directly impacts the efficiency of charge transfer between active materials and external circuits. Metallic foils like copper exhibit high conductivity, typically around 5.96 x 10^7 S/m, but their performance can degrade due to oxidation or mechanical stress. In contrast, freestanding CNT films can achieve conductivities exceeding 10^5 S/m, with graphene films reaching even higher values, up to 10^6 S/m, depending on synthesis methods and post-treatment. The interconnected network of sp2-hybridized carbon atoms in these materials facilitates efficient electron transport, while their porous structure enhances electrolyte accessibility in devices like supercapacitors. For instance, vertically aligned CNT arrays have demonstrated exceptional in-plane conductivity, making them suitable for high-rate applications.

Corrosion resistance is another key advantage of carbon-based current collectors. Metal foils are prone to oxidation and chemical degradation, particularly in harsh electrolytes or under high-voltage operation. Aluminum current collectors, for example, can corrode in lithium-ion batteries when exposed to certain electrolytes, leading to increased internal resistance and capacity fade. Carbon nanomaterials, however, exhibit remarkable chemical inertness. Graphene and CNTs are stable across a wide electrochemical window, resisting degradation even in acidic or alkaline environments. This property extends the lifespan of energy storage devices and enables compatibility with diverse electrolyte systems. Studies have shown that CNT-based current collectors maintain structural integrity after thousands of charge-discharge cycles, with negligible corrosion-related performance losses.

Adhesion between the current collector and active materials is crucial for maintaining low interfacial resistance and preventing delamination during device operation. Metal foils often require surface treatments or conductive additives to improve adhesion, adding complexity to manufacturing processes. Carbon nanomaterials offer inherent advantages in this regard. The high surface area and tunable surface chemistry of CNT and graphene films promote strong physical and chemical interactions with active materials. For example, the fibrous structure of CNT mats provides mechanical interlocking with electrode components, while oxygen-containing functional groups on graphene oxide facilitate bonding with polar materials. This enhanced adhesion minimizes contact resistance and improves cycling stability. In some cases, freestanding CNT films have been used as both current collectors and electrode frameworks, eliminating the need for binders and further simplifying device architecture.

Freestanding CNT films serve as a compelling example of carbon-based current collectors in practice. These lightweight films, often produced through vacuum filtration or floating catalyst chemical vapor deposition, combine high conductivity with mechanical flexibility. Their porous structure allows for efficient ion transport while maintaining electronic percolation pathways. In lithium-sulfur batteries, for instance, freestanding CNT films have replaced aluminum foils, mitigating polysulfide shuttling and reducing overall cell weight. Similarly, in supercapacitors, these films have enabled the development of ultrathin, flexible devices without the constraints of metal foil brittleness.

The mechanical properties of carbon-based current collectors further distinguish them from metal foils. While metals tend to plastically deform under stress, CNT and graphene films exhibit elastic behavior, accommodating repeated bending and folding without permanent damage. This flexibility is particularly valuable for wearable and flexible electronics, where traditional metal foils would fail due to fatigue. The tensile strength of CNT films can exceed 200 MPa, with graphene films reaching even higher values, ensuring structural integrity under mechanical stress.

Thermal management represents another benefit of carbon nanomaterial current collectors. The high thermal conductivity of graphene and CNTs, often exceeding 3000 W/mK for pristine graphene, facilitates heat dissipation in high-power applications. This property helps mitigate thermal runaway risks in batteries and improves the power handling capability of supercapacitors. In contrast, metal foils exhibit lower thermal conductivity, with copper at approximately 400 W/mK, limiting their heat dissipation efficiency.

Scaling up production of carbon-based current collectors remains a challenge, but advances in roll-to-roll manufacturing and solution processing have improved feasibility. Techniques like shear alignment and Langmuir-Blodgett assembly have enabled the production of large-area graphene and CNT films with controlled orientation and properties. While costs currently exceed those of metal foils, the performance benefits and potential for integration with other device components may justify the premium in specialized applications.

Environmental considerations also favor carbon nanomaterials. Unlike metal foils, which require energy-intensive mining and refining processes, carbon-based current collectors can be produced from renewable precursors using relatively low-temperature synthesis methods. Their stability and recyclability further reduce the environmental footprint of energy storage devices.

In summary, the transition from metal foils to lightweight carbon nanotube and graphene films as current collectors addresses multiple limitations of conventional battery and supercapacitor designs. These materials offer a unique combination of high conductivity, corrosion resistance, and strong adhesion while enabling mechanical flexibility and improved thermal management. As synthesis methods mature and costs decline, carbon-based current collectors are poised to play an increasingly important role in advancing energy storage technologies. Their adoption could lead to lighter, more durable, and higher-performance devices across portable electronics, electric vehicles, and grid-scale storage applications.