Mitigation of layer to spinel conversion of a lithium-rich layered oxide cathode by substitution of Al in a lithium ion battery

摘要

The layer to spinel structure conversion of lithium-rich layered oxides during cycling could be alleviated by equal substitution of Al for Mn and Ni, resulting in better capacity retention and average voltage. The Al-doped lithium-rich layered oxide (Li(1.2)Mn(0.6-x)Mn(0.2-x)Al(2x)O(2)x = 0.03) was prepared using an EDTA based sol-gel method. The Al-doped sample exhibited superior capacity retention, 97% at 25 degrees C and 91% at 55 degrees C under a current of 25 mA g(-1) in comparison with the pristine sample, 79 and 78%, respectively. The average voltage of the Al-doped sample could also be improved from 3.36 to 3.39 V after 100 cycles. The reasons for the mitigation of the transformation to a spinel-like impurity were due to less Li/Ni cation mixing and the decreased oxygen loss from the lattice. In addition, Al prefers to be segregated near the surface and prevents unwanted side reactions between the cathode and electrolyte during cycling. According to ex situ electrochemical impedance spectroscopy (EIS), the formation of the SEI (solid electrolyte interphase) layer could be suppressed.