A fluorinated electrolyte additive helps lithium-ion batteries retain 95.6% capacity after 1,000 cycles, offering a targeted approach to longer-lasting energy storage for future battery designs.
Researchers at the Japan Advanced Institute of Science and Technology (JAIST) have developed pentafluorophenyl thiophene imine (FPTI), an electrolyte additive that helps graphite anodes retain 95.6% of their capacity after 1,000 charging cycles. The approach strengthens the protective layer formed on the graphite surface without changing the underlying electrode material.
During the early charging cycles of a lithium-ion battery, electrolyte components react with the graphite anode to form a solid electrolyte interphase (SEI). This layer allows lithium ions to move between the electrolyte and electrode while limiting unwanted chemical reactions. If the SEI becomes unstable, resistance can rise and capacity can decline.
JAIST researchers added FPTI to a conventional lithium-ion electrolyte at concentrations of 2 and 4 mg/ml. The additive reacted preferentially during early cycling, forming a more stable and conductive SEI on the graphite surface.
At the higher concentration, SEI resistance fell from 7.6 ohms in the control cell to 2.2 ohms. Charge-transfer resistance also dropped from 41.8 to 19.8 ohms, while lithium-ion diffusion improved. Surface analysis showed that sulfur- and imine-derived components became incorporated into the protective layer, while the fluorinated portion promoted formation of a lithium-fluoride-rich layer.
The improvement became particularly clear during extended cycling. Cells containing 2 mg/ml and 4 mg/ml FPTI retained 89.4% and 95.6% of their maximum capacity, respectively, after 1,000 cycles. The additive-free control retained only 62.7%.
The researchers also tested FPTI-conditioned graphite anodes in NMC811/graphite full cells. The 4 mg/ml treatment produced an energy density of about 233 Wh/kg, compared with roughly 130 Wh/kg for the control.
The study demonstrates a targeted way to improve graphite-anode durability. Further testing under practical battery conditions will be needed to determine how effectively the approach can translate into longer-lasting commercial lithium-ion batteries.
