Carbon nanotube and graphene electrodes pave the way for next-generation flexible batteries

Engineers have mapped out the future of flexible lithium-ion batteries (FLIBs), showing how carbon nanotubes (CNTs) and graphene can transform rigid power sources into stretchable, foldable, and self-healing energy systems for wearable electronics. The review, published in ENGINEERING Energy (formerly Frontiers in Energy), provides the first systematic analysis of how these advanced carbon materials enable batteries to bend, twist, and adapt to extreme conditions while maintaining high performance.

"Flexible electronics are revolutionizing healthcare, communications, and consumer devices, but they need power sources that can move with them," said corresponding author Yanzhi Cai from Xi'an University of Architecture and Technology. "This review establishes a clear framework for designing batteries that aren't just flexible, but truly multifunctional—capable of self-healing after damage and monitoring their own health."

The research team from Xi'an University of Architecture and Technology and Northwestern Polytechnical University analyzed hundreds of studies to categorize how CNTs and graphene serve three critical roles in FLIB electrodes: as conductive agents that accelerate electron flow, as flexible skeletons that withstand mechanical stress, and as active materials that store energy directly.

Three Structural Paradigms

The study identifies three fundamental electrode architectures, each with distinct advantages:

• Film electrodes: Self-supporting paper-like structures that achieve ultrahigh flexibility, with some demonstrating 180° bending and 720° twisting without capacity loss
• Wire-shaped electrodes: Fiber and yarn configurations that enable weaving batteries into textiles, achieving stretchability up to 100% strain
• Powder electrodes: Core-shell nanostructures that maximize energy density but require careful design to prevent material detachment

"Each structure serves different applications," explained co-author Zhongyi Hu. "Film electrodes excel in medical patches and foldable displays, while wire-shaped batteries can be integrated directly into smart clothing. The key is matching the architecture to the device's mechanical demands."

Extreme Temperature Performance

The review highlights breakthrough applications in harsh environments. Batteries built with CNT-based electrodes maintained 87% capacity at -40°C and showed stable operation at 70°C—critical for polar expeditions and high-temperature industrial monitoring. This temperature resilience stems from the inherent thermal stability of carbon nanomaterials and their stable interface with gel polymer electrolytes.

From Bendable to Intelligent

Beyond mechanical flexibility, the review outlines emerging "smart" functions:

• Self-healing: Batteries that repair themselves after being cut, using hydrogen-bond-rich polymer substrates that reconstruct fractured connections within seconds
• Self-detecting: Integrated sensors that monitor structural health in real-time, detecting damage through piezoresistive effects before failure occurs

A particularly promising design combines CNT sheets with self-healing polymers, achieving 90.3% capacity retention after 200 bending cycles and immediate functional recovery after physical damage.

Challenges and Future Roadmap

Despite impressive progress, the review identifies critical bottlenecks preventing commercialization:

• Cost: Laboratory-scale production remains expensive; scalable manufacturing needs development
• Safety: Preventing short circuits during extreme folding requires advanced gel electrolytes and separator design
• Intelligence: Integrating self-monitoring without compromising energy density remains a technical challenge

The authors propose a development roadmap prioritizing: (1) all-solid flame-retardant electrolytes for enhanced safety, (2) automated weaving processes for textile integration, and (3) standardized lifecycle assessments to guide industrial scale-up.

Significance for Wearable Technology

With the global wearable electronics market projected to exceed $150 billion by 2030, FLIBs represent a key enabling technology. The review provides manufacturers with design principles to create batteries that are not only thin and lightweight but also robust enough for daily deformation while maintaining the energy density of conventional lithium-ion cells.

"Next-generation wearables won't just monitor health—they'll be embedded in our clothing and skin," noted Cai. "The batteries powering them must be equally adaptable. This work shows that carbon nanomaterials are the foundation for making that vision practical and sustainable."

JOURNAL: ENGINEERING Energy (formerly Frontiers in Energy)

DOI

https://doi.org/10.1007/s11708-024-0911-2

Article Link

https://link.springer.com/article/10.1007/s11708-024-0911-2