Influence of electrolyte conductivity on the performance of lithium-ion batteries: An electrochemical impedance analysis using symmetric cells

Lithium-ion batteries are widely used in energy storage applications owing to their high energy density, long cycle life, and efficiency. The electrochemical performance of cylindrical lithium-ion batteries is significantly influenced by the choice of electrolytes. This study examines the impact of four different electrolytes-lithium bis (fluor sulfonyl) imide (LiFSI), lithium hexafluorophosphate (LiPF₆), lithium bis (pentafluoroethanesulfonyl) imide (LiBETI), and lithium tetrafluoroborate (LiBF₄)-on the battery performance by evaluating their influence on the conductivity, resistance components, and overall electrochemical behavior. The ionic conductivity of the electrolytes, measured using evaluation cells, is significantly influenced by the anionic species, with LiFSI exhibiting the highest conductivity among the tested electrolytes. Additionally, electrochemical impedance spectroscopy was performed using symmetric cells to determine the contributions of various resistance components. The results indicate that LiFSI exhibited the highest conductivity and lowest resistance, followed by LiPF₆ and LiBETI, with LiBF₄ exhibiting the poorest performance. The relationship between the ionic conductivity within the electrode and the ionic conductivity of the electrolytes are measured over a wide temperature range, and the tortuosity factors of the electrodes are evaluated. The relationship between the ionic conductivity of the electrolyte and the ionic conductivity in the electrode is consistent across different electrolytes. Furthermore, the ionic resistance in the electrode is determined using the ionic conductivity of the electrolyte and the tortuosity factor of the electrode. Among the studied electrolytes, LiFSI demonstrated the highest ionic conductivity, leading to reduced ionic resistance in the electrode and improved battery performance.