关键词: Li₂MnO₃正极材料, 氟化镁涂层, 循环稳定性, 库仑效率

Abstract:

Cathode material Li₂MnO₃ has received more and more attention owing to its high theoretical capacity (459 mAh·g ^-1). However, the low initial coulombic efficiency and the poor cycle stability hamper its practical application in lithium-ion batteries. Herein, we investigated the crystal structure and electrochemical performance of Li₂MnO₃ by introducing MgF₂ coating layer. The results indicated that the conversion of partial layer Li₂MnO₃ to spinel phase induced by MgF₂ coating could reduce the initial irreversible capacity and improve the first cycle efficiency. The initial coulombic efficiencies of the 0.5wt.%, 1.0wt.%, and 2.0wt.% MgF₂-coated electrodes were 70.1%, 77.5% and 84.9%, respectively, compared with 57.7% of the pristine cathode. The charge-discharge curves showed that the 1.0wt.% MgF₂-modified Li₂MnO₃ delivered the highest charge and discharge capacities, and exhibited the best cycle stability. The capacity retention rate of the 1.0wt.% MgF₂-coated sample was 81% after the 40th cycles, which was much higher than that of the pristine sample (53.6%). The electrochemical impedance spectroscopic data revealed that the MgF₂ coating reduced the rapid deposition of the resistive component and improved the cycle stability of the electrodes.

Key words: Li₂MnO₃ cathode, MgF₂ coating, cycle stability, coulombic efficiency