A pentafluorophenyl thiophene imine compound builds a LiF-rich protective layer that improves lithium-ion transport and long-term battery stability

A newly developed electrolyte additive could help lithium-ion batteries keep graphite anodes stable over prolonged cycling. Researchers synthesized pentafluorophenyl thiophene imine (FPTI), which forms a protective, LiF-rich solid electrolyte interphase on graphite. At 4 mg/mL, FPTI enabled 95.6% capacity retention after 1,000 cycles in graphite/Li half-cells and improved lithium-ion transport. NMC811/graphite full cells using FPTI-conditioned anodes reached an energy density of approximately 233 Wh/kg, highlighting its potential for longer-lasting battery systems.

Lithium-ion batteries power everything from portable electronics to electric vehicles, but their performance gradually declines as repeated charging and discharging alter the interfaces inside the cell. One particularly important interface forms on graphite, the most widely used commercial anode material. During early charging, electrolyte components decompose on the graphite surface and create a solid electrolyte interphase, or SEI. A stable SEI allows lithium ions to pass while protecting the electrode. If it becomes unstable, however, active lithium is consumed, resistance rises, and capacity can fade more quickly.

Researchers led by Professor Noriyoshi Matsumi at the Japan Advanced Institute of Science and Technology investigated whether a purpose-designed electrolyte additive could make this protective layer more durable. This study was made available online on August 31, 2026, in the journal Energy & Fuels. The team, including Assistant Professor Bharat Srimitra Mantripragada and doctoral student Uday Sai Reddi, synthesized pentafluorophenyl thiophene imine (FPTI), a compound containing pentafluorophenyl, thiophene, and imine groups. They added either 2 or 4 mg/mL of FPTI to a conventional lithium-ion battery electrolyte and compared the results with an additive-free control. Electrochemical measurements showed that FPTI preferentially reacts during the initial stages of cycling, helping build a more conductive and stable SEI on graphite. At 4 mg/mL, the SEI resistance fell from 7.6 ohms in the control cell to 2.2 ohms, while charge-transfer resistance decreased from 41.8 to 19.8 ohms. Lithium-ion diffusion also increased markedly. Surface analysis confirmed that sulfur- and imine-derived species from FPTI became incorporated into the interphase, while the fluorinated portion of the molecule promoted a LiF-rich layer. "Together, these components appear to reduce parasitic reactions and support smoother lithium-ion movement across the electrode-electrolyte interface", explained Prof. Matsumi.

The most striking difference emerged during long-term cycling. Graphite/Li half-cells containing 2 and 4 mg/mL FPTI retained 89.4% and 95.6% of their maximum capacities, respectively, after 1,000 cycles. By comparison, the additive-free cells retained 62.7% and showed substantial capacity fading after about 350 cycles. Differential capacity and voltage analyses also indicated less degradation in FPTI-treated graphite electrodes. The researchers then evaluated whether the benefit could translate to a more practical NMC811/graphite full-cell configuration. Because direct exposure of the NMC811 cathode to FPTI increased resistance and impaired performance, the additive was used specifically to form the protective SEI on the graphite anode during precycling. The full cells were then assembled using control electrolyte. In this configuration, the system with graphite conditioned using 4 mg/mL FPTI achieved the best performance, reaching an energy density of about 233 Wh/kg, compared with approximately 192 Wh/kg for 2 mg/mL and 130 Wh/kg for the control.

The findings suggest that small amounts of a carefully designed, anode-targeted additive can substantially improve graphite interface stability without requiring a change in the active anode material itself. Longer-lasting lithium-ion batteries could reduce replacement frequency, lower costs over a device or vehicle's lifetime, and decrease demand for raw materials. The study also highlights an important design consideration: electrolyte additives may benefit one electrode while harming the other, so their chemistry and mode of use must be tailored to the complete battery system. "Overall, the incorporation of FPTI significantly enhanced the electrochemical performance of the graphite half-cells," concluded Prof. Matsumi.

Further work will be needed to validate the approach in larger-format commercial cells and under a wider range of operating conditions. Even so, the study provides a useful molecular strategy for engineering the graphite-electrolyte interface, one of the quiet but decisive battlegrounds in the race toward more durable rechargeable batteries.

Figure 1. FPTI-Derived Protective Interphase
Image Caption: FPTI promotes a stable LiF-rich passivation layer on graphite, improving interfacial stability and cycling performance.
Image Credit: Professor Noriyoshi Matsumi from Japan Advanced Institute of Science and Technology, Japan
Image Source link: https://doi.org/10.1021/acs.energyfuels.6c02613
License Type: Original content
Usage Restrictions: Cannot be used without permission

Figure 2. Improved Cycling Stability with FPTI
Image Caption: FPTI enhances discharge capacity and long-term cycling stability, with 4 mg/mL showing the best performance over 1,000 cycles.
Image Credit: Professor Noriyoshi Matsumi from Japan Advanced Institute of Science and Technology, Japan
Image Source link: NA
License Type: Original content
Usage Restrictions: Cannot be used without permission

Reference

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Funding information

The authors are thankful to the financial support provided by the Ministry of Education, Culture, Sports, and Technology (MEXT), Japan.

September 02, 2026