Key Takeaways & Executive Findings
- •• • Increasing fluorination temperature from 100°C to 250°C raises the F/C ratio and alters C–F bonding, leading to a progressive increase in heat generation in Ah-level pouch cells, with the most pronounced difference occurring in the 0–20% DOD range. • • Highly fluorinated FPC-250 cathodes exhibit more concentrated LiF accumulation during discharge, as evidenced by post-discharge structural characterization at 20% and 80% DOD, which correlates with localized heat generation. • • Kinetic analysis shows that FPC-250 has higher charge-transfer resistance, lower Li+ diffusivity, and a larger nucleation overpotential compared to FPC-100, resulting in stronger polarization and more severe heat generation. • • Regulating fluorination temperature to tune the structure and chemical environment of CFx cathodes is an effective strategy for improving thermal safety, as demonstrated by the direct correlation between fluorination conditions and heat-generation behavior in practical pouch cells.
Abstract
Lithium/fluorinated carbon (Li/CFx) batteries are among the most promising high-energy-density primary batteries, yet substantial heat generation during discharge poses safety concerns, particularly for high-mass-loaded pouch cells. This study systematically investigates the effects of fluorination temperature on the structure and kinetics of fluorinated porous carbon (FPC) cathodes and on heat generation in Ah-level Li/FPC pouch cells. FPC samples with varying degrees of fluorination were synthesized by adjusting fluorination temperature, which influenced not only the F/C ratio but also the C–F bonding configuration, pore structure, and electronic transport capability. Pouch cells employing more highly fluorinated cathodes generated the most heat during discharge, with heat generation exhibiting clear stage dependence, predominantly in the 0–20% depth of discharge (DOD) range. Post-discharge structural characterization and kinetic analysis revealed that highly fluorinated FPC cathodes (FPC-250) undergo more concentrated LiF accumulation, leading to higher charge-transfer resistance, stronger polarization, lower Li+ diffusivity, and higher nucleation overpotential. These factors collectively intensify early-stage heat generation. The study establishes a correlation between fluorination temperature and cathode structure, discharge-product evolution, discharge kinetics, and heat generation, demonstrating that regulating fluorination temperature is an effective strategy for improving the thermal safety of Li/CFx batteries.
1. Introduction
Lithium/fluorinated carbon (Li/CFx) primary batteries offer a theoretical specific energy of 2180 Wh/kg, low self-discharge, and storage stability exceeding 10 years, making them indispensable for aerospace, military, and emergency power applications. However, their commercial deployment in high-rate and high-mass-loading configurations is hindered by substantial exothermic heat generation during discharge, which can lead to electrolyte decomposition, separator shrinkage, and internal short circuits. The intrinsic poor conductivity of CFx cathodes exacerbates polarization and local heat accumulation, posing a critical safety bottleneck that has limited their adoption in larger-format cells.
This study addresses this bottleneck by systematically engineering the fluorination temperature of porous carbon cathodes, which modulates the F/C ratio, C–F bonding configuration, and pore structure. By correlating these structural parameters with heat-generation behavior in Ah-level pouch cells, the research identifies the 0–20% depth of discharge as the critical stage where heat release is most sensitive to cathode fluorination. The findings provide a mechanistic understanding of how LiF accumulation and discharge kinetics govern thermal output, offering a practical pathway to enhance the thermal safety of Li/CFx batteries without compromising energy density.
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Xia Xixian, Li Yu, Sun Lidong, Peng Cong, Kong Lingchen, Wang Yong, Feng Wei (2026). Fluorination Regulates Heat Generation in Ah-Level Lithium/Fluorinated Carbon Pouch Cells. New Carbon Materials. https://doi.org/10.1016/S1872-5805(26)61104-3
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Frequently Asked Questions
What is the quantitative impact of fluorination temperature on the F/C ratio and C–F bonding configuration, and how does this translate to heat generation in pouch cells?
The study demonstrates that increasing fluorination temperature from 100°C to 250°C raises the F/C ratio and shifts C–F bonding toward more covalent configurations. This structural change correlates with a progressive increase in heat generation in Ah-level pouch cells, with the most significant difference observed in the 0–20% DOD range. Specifically, FPC-250 cathodes exhibit higher charge-transfer resistance and lower Li+ diffusivity, leading to stronger polarization and more severe heat release.
How does LiF accumulation during discharge differ between low- and high-fluorination cathodes, and what are the implications for cell performance?
Post-discharge structural characterization at 20% and 80% DOD reveals that highly fluorinated FPC-250 cathodes undergo more concentrated LiF accumulation compared to FPC-100. This localized LiF buildup increases charge-transfer resistance and nucleation overpotential, impairing discharge kinetics and intensifying early-stage heat generation. The inhomogeneous LiF distribution is a key factor in the thermal behavior of high-fluorination cells.
What specific kinetic parameters are affected by higher fluorination, and how do they contribute to heat generation?
Kinetic analysis shows that FPC-250 has a higher charge-transfer resistance, lower Li+ diffusivity, and a larger nucleation overpotential during discharge. These factors collectively lead to stronger polarization, which increases the overpotential and thus the heat generated per unit of discharge capacity. The study quantifies these effects, linking them to the observed heat-generation patterns.
Can the heat-generation behavior be mitigated by optimizing fluorination temperature without compromising energy density?
Yes, the study suggests that regulating fluorination temperature is an effective strategy to tune the structure and chemical environment of CFx cathodes, thereby improving thermal safety. By selecting a lower fluorination temperature (e.g., 100°C), cells exhibit reduced heat generation, particularly in the early discharge stage, while maintaining acceptable energy density. This trade-off must be carefully balanced for specific applications.
What are the scalability implications of these findings for commercial Li/CFx battery manufacturing?
The study uses Ah-level pouch cells, which are representative of practical large-format batteries. The results indicate that fluorination temperature is a critical process parameter that can be adjusted during manufacturing to control heat generation and enhance safety. This provides a straightforward, scalable approach to improve the thermal performance of Li/CFx batteries without requiring major changes to existing production lines.
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