Fibre Batteries Promise Smart Clothing, but Two Key Technical Barriers Block Real-World Use

Two technical constraints are preventing fibre lithium-ion batteries from moving into practical textile applications. Protective housing must block moisture and oxygen, which accelerate lithium-ion battery degradation and reduce effectiveness, without compromising flexibility, while existing models cannot accurately predict the relationship between battery chemistry and maximum effective yarn length. Together, these limits define the current boundary between laboratory capability and garment-scale deployment.

• Researchers evaluated five encapsulation strategies, measuring water vapour transmission rate, cyclic capacity retention, internal resistance and calendar life to test practical viability.
• None of the approaches met all critical requirements, with trade-offs observed across water resistance, flexibility, complexity and cost.
• The study, ‘Toward Real-Life Applications of Fiber Lithium-Ion Batteries’, authored by researchers at NC State University and published in Small, examined both packaging methods and modelling limits affecting textile-scale deployment.

THE STUDY: The paper examined two obstacles preventing fibre-based lithium-ion batteries from reaching practical use despite their promise for wearable applications, focusing specifically on encapsulation performance and mathematical modelling.

• The research evaluated protective housing materials designed to shield lithium-ion components from oxygen and moisture while maintaining the flexibility required for yarn-like structures.
• Four technical indicators were used to assess encapsulation viability: water vapour transmission rate, cyclic capacity retention, internal resistance and calendar life.
• Water vapour transmission rate measures how much moisture can permeate a surface, while cyclic capacity retention reflects a battery’s ability to store energy across repeated charge and discharge cycles.
• The authors included Mengli Wei, Wei Gao, Nanfei He, Seongjin Kim and Andrea Lee, all affiliated with NC State University.

THE TECHNICAL CONSTRAINTS:Encapsulation remains the most pressing issue for fibre battery researchers, though modelling limits also define the current ceiling for fibre lithium-ion battery deployment. Researchers assessed five protective approaches, from polymeric tube sheathing to liquid metal encapsulation, and examined how performance scales with yarn length. Each pathway revealed structural trade-offs that complicate translation from laboratory prototypes to textile manufacturing environments.

• Polymeric tube sheathing and related early-stage methods provided structural containment but lacked one or more critical performance characteristics.
• Liquid metal encapsulation combined high water resistance with flexibility, yet researchers said its complexity and cost prevent practical adoption.
• Experimental findings confirmed a length effect: battery output increases as yarn length grows, but gains eventually plateau.
• Existing mathematical models cannot accurately predict how device variables influence maximum effective length, even when underlying physics is understood.
• The authors said packaging-industry expertise and electrochemical modelling support could help refine both barrier materials and predictive design tools.

WHAT THEY SAID

This is a large industry just focused on packaging, and they have unique techniques to block both oxygen and water. If we can tap into their expertise, it could help us make significant progress on this technology.

— Mengli Wei
Graduate Student, Wilson College of Textiles
NC State University

The length effect is determined by the inherent physics of the fiber battery configuration, which we learned from experimental data. The problem is that the models are not accurate enough to predict the effects of different device variables. If the model is accurate, we can plug in different device parameters, and it can predict the optimal battery length. That way we would be able to provide better guidance when making fiber batteries for practical applications, such as their incorporation in textile fabrics and garments.

— Wei Gao
Associate Professor, Wilson College of Textiles
NC State University