The Fascinating Chemistry of Fluorine in Lithium-ion and Sodium-ion Batteries
Imagine a world where your electric car can travel over 600 miles on a single charge, your smartphone charges in minutes and lasts for days, and grid-scale energy storage makes renewable power available around the clock. This isn't science fiction—it's the future being shaped by a surprising element: fluorine. As the most electronegative element in the periodic table, fluorine possesses unique properties that make it invaluable for advancing battery technology. From extending battery life to enabling higher voltages and enhanced safety, fluorine chemistry serves as an invisible workhorse in both current and next-generation energy storage systems.
Fluorine enables higher energy density, longer cycle life, and improved safety in modern batteries.
Research balances performance with environmental concerns about fluorinated compounds.
Fluorine's remarkable capabilities in battery applications stem from its fundamental atomic properties. With the highest electronegativity of all elements (3.98 on the Pauling scale), fluorine atoms have an exceptional ability to attract electrons 4 6 . This strong electron-pulling power creates more ionic character in chemical bonds, which translates to higher operating voltages in battery materials—a crucial factor for achieving greater energy density.
Fluorine's electronegativity (3.98 Pauling scale) is the highest of all elements, enabling stronger ionic bonds and higher battery voltages.
When incorporated into cathode structures, fluorine enables higher working voltages. For instance, transition metal fluorides like FeF₃ demonstrate theoretical potentials of 2.74 V versus lithium, significantly higher than comparable oxide materials like Fe₂O₃ (1.63 V) 4 .
Fluorinated salts like LiPF₆, LiFSI, and LiTFSI dominate commercial lithium-ion batteries due to their optimal combination of high ionic conductivity, electrochemical stability, and ability to form protective interphases 6 .
A 2025 study published in Nature Communications demonstrated a groundbreaking fluorine-oxygen co-coordination strategy for polymer electrolytes 1 . Researchers developed a fluorinated quasi-solid polymer electrolyte by polymerizing 2,2,3,4,4,4-hexafluorobutyl acrylate (HFA), which features -CF₂ groups that create a unique coordination environment for lithium ions.
In October 2025, researchers from Yonsei University announced the development of a revolutionary fluoride-based solid electrolyte (LiCl–4Li₂TiF₆) that enables all-solid-state batteries to operate safely beyond 5 volts 5 .
at 30°C
after 500 cycles
record-setting figure
Researchers have developed sophisticated fluoride-based cathode materials such as Na₂Fe₂F₇, which features a three-dimensional framework of interconnected FeF₆ octahedra that provides robust pathways for sodium ion diffusion 9 .
A 2025 study in Joule presented a low-cost, fluorine-free electrolyte based on sodium tetrakisphenoxyborate (NaBOPh), synthesized using a simple, scalable one-step method 2 .
The groundbreaking experiment from the Nature Communications study provides a compelling case study in modern fluorine battery research 1 . The research team sought to overcome the limitations of conventional polymer electrolytes, which typically suffer from sluggish ion transport kinetics, particularly at low temperatures.
The experimental results demonstrated remarkable improvements across multiple performance metrics:
| Performance Metric | Fluorinated Polymer | Non-Fluorinated |
|---|---|---|
| Ionic conductivity at -40°C | 0.27 mS cm⁻¹ | 0.2 mS cm⁻¹ |
| Li⁺ transference number | 0.56 | 0.31 |
| Activation energy (Eₐ) | 17.4 kJ mol⁻¹ | 20.3 kJ mol⁻¹ |
| Capacity retention (200 cycles) | 86% | - |
| Material Category | Specific Examples | Key Functions and Applications |
|---|---|---|
| Fluorinated Salts | LiPF₆, LiFSI, LiTFSI, NaPF₆ | High ionic conductivity, electrochemical stability, Al current collector protection 6 |
| Fluorinated Solvents/Additives | FEC, TTE, OS3®, Koflyte® series | SEI/CEI formation, high-voltage stability, flame retardance, thermal stability 3 |
| Fluorinated Binders | PVDF, PTFE | Electrode integrity, binding active materials to current collectors |
| Fluorine-Free Alternatives | LiBOB, NaBOPh, organic anions | Reduced toxicity, lower cost, easier recycling 2 6 |
| Fluorinated Cathode Materials | FeF₃, Na₂Fe₂F₇, fluorinated polyanions | Higher operating voltage, increased energy density 4 9 |
Optimizing balance between performance, cost, safety, and environmental impact
Growing interest in fluorine-free alternatives for sustainable electrochemistry
Continued innovation in fluorinated compounds for energy density and stability
Fluorine chemistry continues to be a cornerstone of battery technology, enabling the high performance, safety, and reliability that modern energy storage applications demand. From extending operational temperature ranges to enabling higher voltage operation and stabilizing reactive interfaces, fluorine-containing compounds address multiple critical challenges simultaneously.
The recent breakthroughs in fluorinated polymer electrolytes and fluoride-based solid electrolytes demonstrate that there remains significant untapped potential in fluorine chemistry for advancing battery technology.
The ideal battery of the future may not be exclusively fluorinated or fluorine-free, but rather intelligently designed systems that strategically deploy fluorine only where its unique properties provide indispensable benefits.
Fluorine will continue to shock the energy storage world with its powerful capabilities for years to come, playing a crucial role in our transition to a clean energy future.