Manipulating the Li/Ni/Fe mixed configuration promotes structure stability of Li-rich layered oxides

Abstract

Lithium-rich layered oxides (LLOs) are highly promising for applications in Li-ions batteries as the cathode materials due to their high energy density. However, LLOs often suffer from significant capacity and voltage loss due to the instability of the layered structure when in the deep extraction state. This inherent instability poses a considerable challenge to their practical application. Herein, a distinctive Li/Ni/Fe mixed configuration was constructed by using the exchange mechanism of Fe ions with Li and Ni ions in the Li layer. This configuration not only improves structural stability, but also expands the layer spacing to accelerate Li⁺ diffusion. Density functional theory (DFT) calculations indicate that the presence of Li/Ni/Fe mixed configuration leads to more Li − O − Li configurations and decreasing the characteristic energy gap above the Fermi energy level. This configuration also effectively increases the migration energy barrier of transition metal (TM) ions and oxygen (O) vacancy formation energy, which reducing the irreversible migration of TM ions and the escape of O. The target material exhibits high-capacity retention of 82.1 % after 300 cycles at 1C, accompanied by a minimal voltage fading rate of just 0.33 mV/cycle. This study offers innovative strategies to enhance the stability of LLOs, facilitating their widespread commercial use.