New Battery Design Resolves Safety-Performance Tradeoff in Lithium Metal Batteries

A research team has developed a lithium fluoride (LiF)-rich protective layer that stabilizes lithium metal anodes against corrosive flame-retardant additives, enabling batteries that are both fire-safe and durable. The breakthrough addresses a fundamental conflict in battery design where safety enhancements typically degrade performance, potentially accelerating the adoption of high-energy lithium metal batteries for electric vehicles and grid storage applications.

Lithium metal batteries offer exceptional energy density but face challenges including dendrite growth, unstable interfaces, and flammable electrolytes. While gel polymer electrolytes with flame retardants like triphenyl phosphate (TPP) improve safety, high concentrations of these additives corrode the anode through the solid electrolyte interphase (SEI), dramatically shortening battery life. The study, published on September 23, 2025, in Carbon Energy (DOI: 10.1002/cey2.70077), demonstrates how combining a dual-confinement electrolyte with a pre-engineered LiF shield resolves this tradeoff.

Researchers from Hebei University of Science and Technology, City University of Hong Kong, and Hainan University created a gel polymer electrolyte containing 70% TPP using coaxial electrospinning. The design features a TPP/PVDF-HFP core encased in a PAN/PVDF-HFP shell, where chemical interactions and physical containment limit TPP leakage while maintaining flame retardancy. To protect the anode, they immersed lithium metal in a 5% fluoroethylene carbonate electrolyte to form a uniform, dense LiF-rich SEI layer.

Analytical techniques including UV–vis spectroscopy, TOF-SIMS, XPS, and AFM confirmed the engineered SEI blocks penetration of TPP-derived species and reduces anode corrosion depth. Beyond protection, the LiF layer enhances lithium-ion mobility, lowers activation energy for interfacial transport, and promotes dendrite-free plating. Electrochemical testing showed Li||Li cells operating 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 maintained 81.7% capacity after 6000 cycles at 10 C, demonstrating exceptional endurance under fast-charging conditions. "The study compellingly shows that precise interface engineering is essential to advancing both the safety and durability of lithium metal batteries," said the lead corresponding scientist. "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 strategy represents a promising direction for developing high-performance, intrinsically safer lithium metal batteries suitable for electric vehicles, grid-level storage, aerospace systems, and flexible pouch cells. The design principle—merging chemical confinement, structural encapsulation, and deliberate SEI engineering—could 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 practical adoption of lithium metal technologies. The research was supported by multiple Chinese funding agencies including the National Natural Science Foundation of China and provincial science programs.