Abstract:

To address the rapid degradation of high-voltage lithium cobalt oxide (LCO) performance caused by crystal structure deterioration and intensified side reactions, this study introduces a novel multifunctional electrolyte additive, 2,6-pyridinitrile (DCPY), to enhance electrode/electrolyte interface stability. The electrode interface, electrolyte physical properties, and electrochemical characteristics of the battery are analyzed using scanning electron microscopy, transmission electron microscopy, electrochemical techniques, and theoretical calculations. The findings reveal that as a multifunctional electrolyte additive, DCPY forms a highly stable interfacial film on both positive and negative electrodes, effectively suppressing electrode/electrolyte interface side reactions and preventing the dissolution and deposition of transition metals. Additionally, the pyridine functional groups in DCPY interact with phosphorus pentafluoride in the electrolyte, substantially reducing corrosion caused by hydrofluoric acid (HF) at both electrode interfaces. This interaction enhances the high-voltage stability of commercial LCO pouch cells. As a result, adding 0.5% DCPY to the base electrolyte solution (Base) optimizes cycling performance in commercial pouch cells (Base + DCPY), increasing capacity retention from 80% to 90% after 800 cycles at 25 ℃ and from 80% to 85% after 600 cycles at 45 ℃. Furthermore, DCPY substantially mitigates gas generation issues during high-temperature operation. Even at an increased operating voltage of up to 4.55 V, LCO//Gr (graphite) pouch cells maintain excellent cycling stability under elevated temperatures. This study presents a practical strategy for developing high-voltage energy storage batteries with high energy density.

Key words: lithium ion battery, lithium cobalt oxide, high voltage, electrolyte additive, 2,6-pyridinedicarbonamide