Facile SEI Improvement in the Artificial Graphite/LFP Li-Ion System: Via NaPF 6 and KPF 6 Electrolyte Additives

In this work, graphite anodes and lithium iron phosphate (LFP) cathodes are used to examine the effects of sodium hexafluorophosphate (NaPF 6 ) and potassium hexafluorophosphate (KPF 6 ) electrolyte additives on the formation of the solid electrolyte interphase and the performance of lithium-ion batteries in both half-cell and full-cell designs. The objective is to assess whether these additives may increase cycle performance, decrease irreversible capacity loss, and improve interfacial stability. Compared to the control electrolyte (1.22 M Lithium hexafluorophosphate (LiPF 6 )), cells with NaPF 6 and KPF 6 additives produced less SEI products, which decreased irreversible capacity loss and enhanced initial coulombic efficiency. Following the formation of the solid electrolyte interphase, the specific capacity of the control cell was 607 mA·h/g, with 177 mA·h/g irreversible capacity loss. In contrast, irreversible capacity loss was reduced by 38.98% and 37.85% in cells containing KPF 6 and NaPF 6 additives, respectively. In full cell cycling, a considerable improvement in capacity retention was achieved by adding NaPF 6 and KPF 6 . The electrolyte, including NaPF 6 , maintained 67.39% greater capacity than the LiPF 6 baseline after 20 cycles, whereas the electrolyte with KPF 6 demonstrated a 30.43% improvement, indicating the positive impacts of these additions. X-ray photoelectron spectroscopy verified that sodium (Na + ) and potassium (K + ) ions were present in the SEI of samples containing NaPF 6 and KPF 6 . While K + did not intercalate in LFP, cyclic voltammetry confirmed that Na + intercalated into LFP with negligible impact on the energy storage of full cells. These findings demonstrate that NaPF 6 and KPF 6 are suitable additions for enhancing lithium-ion battery performance in the popular artificial graphite/LFP system.