A new study published in Carbon Energy demonstrates a finely tuned strategy that stabilizes lithium metal anodes by building a LiF-rich artificial solid electrolyte interphase (SEI), countering the corrosive effects of flame-retardant additives and pointing to a practical route for creating long-lasting, inherently fire-safe lithium metal batteries. The research, detailed in the study published on September 23, 2025, with DOI 10.1002/cey2.70077, addresses a critical challenge: lithium metal batteries promise exceptional energy density, but their performance often collapses when high levels of flame-retardant additives like triphenyl phosphate (TPP) are introduced for safety.
Lithium metal's high theoretical capacity is challenged by dendrite growth, unstable interfacial chemistry, and conventional electrolyte flammability. While gel polymer electrolytes address some safety concerns, they rely on large quantities of flame retardants. Organic phosphates such as TPP enhance fire resistance but tend to penetrate the SEI, triggering decomposition reactions that severely corrode lithium, dramatically shortening battery life at high concentrations. Researchers from Hebei University of Science and Technology, City University of Hong Kong, and Hainan University have reported significant advancement in electrolyte–anode interface engineering to ensure both flame retardancy and long-term anode stability.
The team designed a high-TPP-loading flame-retardant gel polymer electrolyte and paired it with a pre-formed LiF-rich SEI on lithium metal. This combined strategy suppresses corrosion, accelerates Li⁺ transport, and enables stable cycling even at high current densities. They developed a gel polymer electrolyte containing 70 wt.% TPP using a coaxial electrospinning technique, featuring a TPP/PVDF-HFP composite core encased within a PAN/PVDF-HFP shell. This dual-confinement design maintains high flame retardancy while curbing corrosive side reactions typically triggered by TPP.
To further fortify the anode interface, researchers immersed lithium metal in a 5% FEC-containing electrolyte, producing a uniform, dense LiF-rich SEI layer. Multi-modal analyses showed this engineered SEI blocks TPP-derived species penetration and substantially reduces anode corrosion depth. The LiF layer enhances lithium-ion mobility, lowers activation energy for interfacial transport, and promotes smooth, dendrite-free plating. Electrochemical tests validated the design: 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% 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 stated, "The study compellingly shows that precise interface engineering is essential to advancing both the safety and durability of lithium metal batteries. By integrating a dual-confinement flame-retardant electrolyte with a LiF-rich artificial SEI, we resolved 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. Its ability to sustain thousands of cycles at high current densities positions it well for electric vehicles, grid-level storage, aerospace systems, and next-generation flexible pouch cells. More broadly, the underlying design principle—merging chemical confinement, structural encapsulation, and deliberate SEI engineering—can 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. The original research is available at https://doi.org/10.1002/cey2.70077.
