A Unique Formation Process on Rapidly Activating Oxygen Redox in Co-Free Li-Rich Layered Cathodes for Long-Cycle Batteries

Abstract

The utilization of oxygen redox in a Co-free Li-rich layered cathode usually needs to enhance the upper voltage to over 4.6 V, which results in structural changes and electrolyte requests. It is necessary to find a suitable formation method in full batteries that can quickly activate oxygen redox to balance the available capacity and optimal voltage. Here, a series of formation methods with two charge-discharge cycles under cut-off voltage 4.5-4.7 V are explored in practical pouch cells. A tiny voltage plateau appeared at 4.58 V was observed after the formation methods, which did not damage the material’s structure intensity in the first cycle. The surface of the cathode was found to form a thin film of spinel structure during the first charge-discharge process which would support the structure to endure a voltage higher than 4.58 V in the second charge-discharge and completely activate the capacity of Li-rich cathode. According to this guidance, a new formation method was adopted by controlling the cut-off voltage during the cycle process. The new strategy achieves a discharge-specific capacity of 214 mAh.g-1 and capacity retention of 99.0% after 500 cycles under 0.5C. This method shows great advantages in time cost, capacity retention, and Coulomb efficiency.