A research group led by Prof. LIU Zhaoping at the Ningbo Institute of Materials Technology and Engineering of the Chinese Academy of Sciences, in cooperation with international collaborators, revealed that the metastable state of cycled lithium-rich (Li-rich) layered cathode oxides, which stems from structural defects, accounts for the voltage decay of rechargeable lithium-ion batteries (LIBs).

In recent decades, rechargeable LIBs have commercially dominated the portable electronics market, and gradually evolved into the most encouraging market areas for electric vehicles (EVs). However, the energy density and cycle life of state-of-the-art LIBs are limited by low capacities of classical layered oxides, thus have to be further enhanced to satisfy commercial demands for transportation applications. Furthermore, voltage decay upon cycling in Li-rich layered cathodes remains the most hindering obstacle, in which defect electrochemistry plays an indispensable role. 

Delving into the structure mechanism of cycled Li-rich layered cathode oxides, the researcher revealed the unique metastable structure of cycled anionic redox-based cathodes and the impact of thermal energy on energy recovery after extended cycles.

They adopted an effective approach, mild heat treatment, to drive the metastable state close to the pristine state. Density Functional Theory (DFT) calculations of Li-rich layered oxide structure for different states served to illustrate that the cycled state with defects is a dynamical system.

Besides, they demonstrated a direct causation between structural defects and voltage decay in Li-rich layered oxides. 

The study, published in Cell Reports Physical Sciences, illuminated metastability and reversibility of Li-rich layered oxides，providing feasible and efficient solutions for the voltage decay in designing Li-rich layered cathode materials for rechargeable LIBs.