New additive helps lithium-ion batteries retain 95.6% capacity after 1,000 cycles

A new electrolyte additive helped graphite anodes retain up to 95.6% of their capacity after 1,000 charging cycles, pointing to a way to make lithium-ion batteries last longer without changing the graphite itself. Researchers at the Japan Advanced Institute of Science and Technology (JAIST) designed a compound called pentafluorophenyl thiophene imine, or FPTI, to improve the protective layer that forms on graphite during the first few charging cycles. This layer, known as the solid electrolyte interphase (SEI), is critical to battery life. It allows lithium ions to move between the electrolyte and electrode while limiting unwanted chemical reactions. When the SEI becomes unstable, it can consume active lithium and increase resistance, accelerating capacity loss. The researchers added FPTI to a conventional lithium-ion battery electrolyte at concentrations of 2 and 4 milligrams per milliliter. They found that the additive reacted preferentially during early cycling and helped create a more conductive and stable SEI on the graphite surface. Fluorine builds stronger battery shields At the higher concentration, the SEI resistance dropped from 7.6 ohms in the control cell to 2.2 ohms. Charge-transfer resistance also fell from 41.8 to 19.8 ohms, while lithium-ion diffusion increased. The researchers found that different parts of the FPTI molecule contributed to the protective layer. Sulfur- and imine-derived compounds became incorporated into the interphase, while its fluorinated component helped create a lithium fluoride-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 improvement became clearer during extended cycling. Graphite cells containing 2 milligrams per milliliter of FPTI retained 89.4% of their maximum capacity after 1,000 cycles. Cells using 4 milligrams per milliliter retained 95.6%. The additive-free control retained only 62.7% and began showing substantial capacity loss after about 350 cycles. The team then tested whether the approach could work in a full battery using an NMC811 cathode and graphite anode. This exposed an important limitation: putting FPTI directly into the full-cell electrolyte increased resistance at the cathode and hurt performance. Instead, the researchers used FPTI only to precondition the graphite anode. They formed the improved SEI during precycling and then assembled the full cells using the standard electrolyte. Targeted chemistry boosts full-cell output That approach produced a substantial difference in energy density. The full cell using graphite preconditioned with 4 milligrams per milliliter of FPTI reached about 233 Wh/kg. The 2 milligrams per milliliter treatment reached roughly 192 Wh/kg, while the control managed about 130 Wh/kg. The result highlights why battery additives cannot simply be judged by their effect on one electrode. A chemical that improves the graphite-electrolyte interface may create problems at the cathode, making targeted treatment potentially more useful than adding the compound throughout the cell. “Overall, the incorporation of FPTI significantly enhanced the electrochemical performance of the graphite half-cells,” concluded Prof. Matsumi. The researchers say larger commercial-format cells and broader operating conditions will be needed to determine whether the strategy can translate into practical batteries. Still, the work shows how molecular-level control of the graphite surface could extend battery life without replacing the widely used anode material. The study is published in Energy & Fuels. Get the latest in engineering, tech, space & science - delivered daily to your inbox.With over a decade-long career in journalism, Neetika Walter has worked with The Economic Times, ANI, and Hindustan Times, covering politics, business, technology, and the clean energy sector. Passionate about contemporary culture, books, poetry, and storytelling, she brings depth and insight to her writing. When she isn’t chasing stories, she’s likely lost in a book or enjoying the company of her dogs.