3 Breakthroughs in One: Non-Flammable, Wide-Temperature Lithium Battery Electrolyte Unveiled
In a development poised to reshape the safety and performance benchmarks of electric vehicles and grid-scale energy storage, Chinese researchers have engineered a next-generation lithium-ion battery electrolyte that simultaneously solves three longstanding industry challenges: flammability, poor low-temperature performance, and graphite anode incompatibility. The innovation—centered on a modified formulation using diethyl ethylphosphonate (DEEP)—delivers a rare trifecta: it is non-flammable, remains liquid down to –60°C, and enables stable cycling of conventional graphite-based cells without exotic additives or ultra-high salt concentrations.
For automotive engineers and battery investors, this represents more than incremental progress. It signals a potential pivot away from the volatile carbonate solvents that have powered the EV revolution but also fueled safety concerns following high-profile battery fires in vehicles and stationary storage systems. The new electrolyte, detailed in a peer-reviewed study published in Energy Storage Science and Technology, could accelerate the adoption of safer, all-climate lithium-ion batteries—particularly in regions with extreme winters or where fire risk mitigation is non-negotiable.
At the heart of the breakthrough is a sophisticated yet scalable approach to electrolyte solvation engineering. Rather than relying on expensive ionic liquids, fluorinated solvents, or highly concentrated “water-in-salt” analogs that drive up cost and viscosity, the team from State Grid Anhui Electric Power Research Institute and Huazhong University of Science and Technology leveraged the inherent advantages of DEEP—a low-cost, non-flammable phosphate derivative—while neutralizing its historical Achilles’ heel: incompatibility with graphite anodes.
Previous attempts to integrate phosphate-based flame retardants like triethyl phosphate (TEP) or DEEP into carbonate electrolytes often failed because these molecules bind too strongly to lithium ions (Li⁺). This strong interaction pulls them into the primary solvation shell—the immediate molecular environment around each Li⁺ ion—where they inevitably decompose on the graphite surface during the first charge cycle. The resulting solid electrolyte interphase (SEI) is electronically “leaky,” allowing continuous electrolyte reduction, rapid capacity fade, and eventual anode failure.
The researchers circumvented this by orchestrating a precise molecular choreography. They introduced ethylene carbonate (EC), a high-donor-number solvent known for its excellent SEI-forming ability, to compete with DEEP for coordination sites around Li⁺. Simultaneously, they added methyl trifluoroethylene carbonate (FEMC), a weakly coordinating linear carbonate, which—through the coordination number rule—helps pull more anions (specifically FSI⁻ from lithium bis(fluorosulfonyl)imide, or LiFSI) into the solvation shell. The result is a dynamic equilibrium where DEEP is effectively “pushed out” of the inner solvation layer, minimizing its presence at the anode interface.
This dual-solvent strategy yielded dramatic results. In a conventional-concentration electrolyte (~1.15 mol/L), graphite half-cells retained 95.6% of their capacity after 150 cycles—a performance level comparable to standard commercial electrolytes but with none of the fire risk. Even more compelling for automotive applications, full cells paired with lithium iron phosphate (LFP) cathodes demonstrated robust operation at subzero temperatures. At –20°C, these cells delivered a first-cycle discharge capacity of 70 mAh/g and maintained 49.3% capacity retention after 50 cycles—far outperforming conventional carbonate electrolytes, which essentially freeze and become electrochemically inert under the same conditions.
Crucially, the formulation remains non-flammable. In open-flame tests, standard carbonate electrolytes ignited instantly and burned vigorously, while the DEEP-based blend showed no ignition even after prolonged exposure. Its self-extinguishing time was recorded as 0 seconds per gram—effectively eliminating one of the primary triggers of thermal runaway cascades in battery packs.
From a manufacturing standpoint, the electrolyte’s compatibility with existing cell architectures is a major advantage. It uses graphite anodes and LFP cathodes—two of the most widely deployed, cost-effective, and supply-chain-resilient materials in today’s EV and energy storage markets. No exotic binders, artificial SEI coatings, or dry-room assembly modifications are required. This “drop-in” potential significantly lowers the barrier to commercialization.
The implications extend beyond passenger vehicles. Grid-scale battery energy storage systems (BESS), which have faced growing scrutiny after incidents in Australia, South Korea, and the United States, could benefit immensely from a non-flammable electrolyte that also performs reliably in cold climates. Similarly, commercial electric fleets—delivery vans, buses, and trucks operating in northern latitudes—often suffer reduced range and charging inefficiencies in winter. A battery that maintains ion conductivity and interfacial kinetics at –40°C could mitigate these operational headaches.
While the research is still at the laboratory scale, the chemistry is built on commercially available components. DEEP, LiFSI, EC, and FEMC are all produced at industrial volumes, though FEMC remains more expensive than standard linear carbonates like EMC or DMC. However, the team’s use of only a 1.15 mol/L salt concentration—far below the 3–5 mol/L typical of “high-concentration” non-flammable electrolytes—helps offset material costs. Moreover, the elimination of fluorinated co-solvents or ionic liquids further enhances economic viability.
Independent battery analysts note that the real test will be long-term cycling under real-world conditions, including high-voltage operation, fast charging, and mechanical stress. The current study focused on LFP, which operates at a modest 3.2 V. Compatibility with nickel-rich NMC or high-voltage spinel cathodes remains unproven. Nevertheless, the foundational solvation design principle—using competitive coordination to exclude problematic solvents from the Li⁺ shell—could be adapted to other chemistries.
Regulatory and insurance stakeholders are also watching closely. As global safety standards for EVs and BESS tighten—particularly in Europe and North America—the ability to demonstrate intrinsic non-flammability at the cell level could translate into lower certification hurdles, reduced insurance premiums, and enhanced consumer confidence. Unlike external fire-suppression systems or cell-to-pack design mitigations, this approach addresses the hazard at its source: the electrolyte itself.
For China, the world’s largest EV market and battery producer, this development aligns with national priorities around energy security, technological self-reliance, and industrial safety. State Grid’s involvement underscores the utility sector’s interest in safer stationary storage, while the academic-industry collaboration model reflects Beijing’s push for applied innovation in strategic sectors. If scaled successfully, the technology could become a key export, particularly to emerging markets seeking affordable, safe, and climate-resilient energy storage.
Looking ahead, the researchers suggest further optimization is possible. Minor additives like lithium difluoro(oxalato)borate (LiDFOB) and vinylene carbonate (VC)—already common in commercial electrolytes—were used in full-cell testing to stabilize the cathode interface, indicating the formulation can integrate with existing additive packages. Future work may explore solvent ratios to balance low-temperature fluidity with high-temperature stability, or investigate recycling compatibility.
In an industry often torn between performance, safety, and cost, this DEEP-based electrolyte offers a rare convergence. It doesn’t demand trade-offs; it redefines what’s possible within a conventional cell format. For automakers racing to deliver safer, longer-range, all-weather EVs—and for investors betting on the next leap in battery tech—this could be the chemistry that finally turns the page on flammable electrolytes.
Wang Shuping¹, Yang Xiankun²,³, Li Changhao¹, Zeng Ziqi², Cheng Yifeng¹, Xie Jia²
¹State Grid Anhui Electric Power Research Institute, Anhui Province Key Laboratory of Electric Fire and Safety Protection (State Grid Laboratory of Fire Protection for Transmission and Distribution Facilities), Hefei 230601, Anhui, China
²State Key Laboratory of Advanced Electromagnetic Technology, School of Electrical and Electronic Engineering, Huazhong University of Science and Technology
³School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430000, Hubei, China
Energy Storage Science and Technology, 2024, 13(7): 2161–2170
DOI: 10.19799/j.cnki.2095-4239.2024.0117