Faster Activation and Slower Capacity/Voltage Fading: A Bifunctional Urea Treatment on Lithium-Rich Cathode Materials

摘要

Li-rich layered oxides are promising cathode materials for next-generation Li-ion batteries because of their extraordinary specific capacity. However, the activation process of the key active component Li2MnO3 in Li-rich materials is kinetically slow, and the complex phase transformation with electrode/electrolyte side reactions causes fast capacity/voltage fading. Herein, a simple thermal treatment strategy is reported to simultaneously tackle these challenges. The introduction of a urea thermal treatment on Li-rich material Li1.87Mn0.94Ni0.19O3 leads to oxygen deficiencies and partially reduced Mn ions on the oxide surface for activating the Li-rich phase. In situ synchrotron study confirms that the urea-treated cathode shows much faster Li extraction from both Li and transition metal layers with less oxygen evolution upon charging than that of untreated counterparts. Moreover, the decomposition products of urea during thermal treatment subsequently deposit on the surface of cathode material, leading to a unique passivation layer against side reactions between electrode and electrolyte. Soft X-ray absorption spectroscopy reveals the structural evolution mechanism with a significantly suppressed dissolution of Mn species over cycling measurement. The urea-treated Li1.87Mn0.94Ni0.19O3 shows accelerated activation kinetics to reach high capacity of 270 mA h g(-1) and demonstrates excellent capacity retention of 98.49% over 300 cycles with slower voltage decay.