富锂层状正极材料Li2MnO3的表面改性及其电化学性能研究

Electrochemical Performance Improvement of Li2MnO3 Cathode Materials by MgF2 Coating

Li2MnO3正极材料具有较高的理论容量(459 m Ah·g^-1),不仅安全无毒还能够大大降低电池的制造成本,从而受到越来越多的关注.然而,较低的首圈库仑效率和较差的循环性能妨碍了其在锂电池中的实际应用.在此,作者研究了MgF2涂层对Li2MnO3正极材料的电化学性能.结果表明,MgF2涂层诱导部分层状Li2MnO3向尖晶石相转化,从而降低了首圈不可逆容量,提高库仑效率.重量比为0.5%、1.0%和2.0%的MgF2涂层电极的初始库仑效率分别为70.1%、77.5%和84.9%,而原始电极仅为57.7%.充放电曲线表明,1.0wt.%MgF2涂层改性的Li2MnO3具有最高的充放电容量和最佳的循环稳定性. 40个循环后1.0wt.%MgF2涂层样品的容量保持率为81%,远高于原始样品的容量保持率(53.6%).电化学阻抗谱结果表明MgF2涂层减少了不利成分的快速沉积,并改善了电极的循环稳定性.

Cathode material Li2MnO3 has received more and more attention owing to its high theoretical capacity(459 m Ah·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 0.5 wt.%, 1.0 wt.%, and 2.0 wt.%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 1.0 wt.% MgF2-modified Li2MnO3 delivered the highest charge and discharge capacities,and exhibited the best cycle stability. The capacity retention rate of the 1.0 wt.% MgF2-coated sample was 81% after the 40 th 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.