Raising the concentration of the electrolyte additive vinylene carbonate (VC) can significantly extend the lifetime of lithium iron phosphate (LFP)/graphite pouch cells cycled at high temperatures, according to a study published in the Journal of The Electrochemical Society. The research, led by battery scientist Saad Azam, evaluated VC concentrations from 1% to 5% in cells cycled at 70°C, a condition that accelerates degradation and is increasingly relevant as LFP chemistry gains traction in electric vehicles and grid energy storage.
The study found that higher VC concentrations substantially improved cell lifetime, reduced iron dissolution from the positive electrode, and suppressed electrolyte degradation pathways. Specifically, the additive curbed the formation of ethyl methyl carbonate (EMC) and dimethyl 2,5-dioxahexane carboxylate (DMOHC), two products that signal electrolyte breakdown. Post-mortem analyses, including quantitative nuclear magnetic resonance (qNMR) and gas chromatography-mass spectrometry (GC-MS), were used to track changes in electrolyte composition after the cells reached end-of-life, defined as 80% capacity retention.
Iron deposition on the negative electrode, a key degradation mechanism in LFP cells, was quantified using micro X-ray fluorescence (μXRF). Electrochemical impedance spectroscopy (EIS) assessed charge-transfer resistance. The experiments covered a broad range of cell designs: four distinct graphite types, two variations in LFP surface area, and two cell form factors, all in pouch cell format. This diversity strengthens the finding that the benefits of higher VC loading are not limited to a single configuration.
The study also compared two lithium salts, LiFSI and LiPF6. While LiFSI-based LFP/graphite cells showed enhanced performance in certain metrics, they suffered from gas production at 70°C. That gas generation could be mitigated by incorporating LiPF6 salt, suggesting a practical pathway for electrolyte formulation in high-temperature applications.
Saad Azam completed his PhD at Dalhousie University in the Jeff Dahn research group, where his work focused on electrolyte additives, high-temperature degradation, transition-metal dissolution, gas evolution, and long-term cycling of LFP/graphite and NMC/graphite pouch cells. His research combines electrochemical testing with advanced post-mortem methods to link cell performance with chemical degradation mechanisms.
The findings carry implications for the design of longer-lasting batteries for electric vehicles and stationary storage, where high-temperature operation can shorten life and raise safety concerns. By identifying VC concentration as a lever to reduce iron dissolution and electrolyte breakdown, the study offers a concrete direction for electrolyte optimization in LFP/graphite systems.
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