LiF-Armored Lithium Anode Enables Ultra-Stable, Fire-Safe Batteries

A new study published in Carbon Energy on September 23, 2025, presents a finely tuned strategy that stabilizes lithium metal anodes by building a LiF-rich artificial solid electrolyte interphase (SEI), countering corrosive effects from flame-retardant additives while maintaining exceptional cycling stability. The research, conducted by teams from Hebei University of Science and Technology, City University of Hong Kong, and Hainan University, addresses a critical challenge in battery development: how to achieve both fire safety and long-term performance in high-energy-density lithium metal batteries.

Lithium metal batteries offer exceptional theoretical capacity but face real-world challenges including dendrite growth, unstable interfacial chemistry, and the flammability of conventional electrolytes. While gel polymer electrolytes improve safety, they typically require large quantities of flame retardants like triphenyl phosphate (TPP), which enhance fire resistance but tend to penetrate the SEI and trigger decomposition reactions that severely corrode lithium. This corrosion dramatically shortens battery life, creating a pressing need for interface and electrolyte designs that ensure both flame retardancy and long-term anode stability.

The researchers developed a high-TPP-loading flame-retardant gel polymer electrolyte using a coaxial electrospinning technique, creating a dual-confinement design with a TPP/PVDF-HFP composite core encased within a PAN/PVDF-HFP shell. This structure, detailed in the study published at https://doi.org/10.1002/cey2.70077, maintains high flame retardancy while curbing corrosive side reactions through strong chemical interactions and physical containment. To further fortify the anode interface, the team immersed lithium metal in a 5% FEC-containing electrolyte, producing a uniform and dense LiF-rich SEI layer that blocks TPP penetration and substantially reduces anode corrosion.

Electrochemical testing validated the design's effectiveness. Li||Li cells operated stably for 2400 hours at 0.5 mA cm⁻² and 1500 hours at 5 mA cm⁻². In full-cell configurations, LFP||Li cells retained 98.9% of their capacity after 1500 cycles at 1 C and preserved 81.7% capacity after 6000 cycles at 10 C, demonstrating exceptional endurance under fast-charging conditions. The lead corresponding scientist noted that precise interface engineering is essential to advancing both safety and durability, stating that integrating dual-confinement flame-retardant electrolyte with a LiF-rich artificial SEI resolves the long-standing conflict between fire protection and anode stability.

This combined SEI-electrolyte strategy represents a promising direction for developing high-performance, intrinsically safer lithium metal batteries suitable for electric vehicles, grid-level storage, aerospace systems, and next-generation flexible pouch cells. The underlying design principle—merging chemical confinement, structural encapsulation, and deliberate SEI engineering—can potentially be applied to other reactive anodes and high-voltage cathodes. As global demand for high-energy batteries intensifies alongside strict safety requirements, this approach may accelerate the practical adoption of lithium metal technologies that have previously been limited by safety-performance tradeoffs.