Local electronic structure modulation enhances operating voltage in Li-rich cathodes

Abstract

Lithium-rich materials, which exhibit high capacity due to the existence of anionic redox, are in highly demanded for high energy density Li ion batteries. Nevertheless, the low operating voltage and rapid voltage drop of Li-Rich cathodes are seen as the fatal issues, which result in reduced energy density and degraded energy quality of the batteries, limiting their further commercial application. Herein, we focus on the local electronic structure controlled by chemical composition (to prepared high Ni content Li-rich cathode) to improve the operating voltage and suppress voltage decay. Through detailed physical characterization, electrochemical analysis and theoretical calculations, we summarize three main factors for improving the voltage of lithium-rich materials: 1) Increasing the O-Ni2+/3+/Li+ content effectively regulates the coordination environment of oxygen in Li-rich materials, realizes the regulation of local electronic structure; 2) the substitution of Ni increases the oxidation state of TM ions, especially for Mn, to keep charge balance, so as to improve the operating voltage and suppress voltage decay; 3) adjusting local electronic structure shifts the TM 3d-O 2p bands and the non-bonding O 2p band to lower energy, leading to an increase in the redox reaction potential. This strategy provides a method to regulate the coupling reaction of cation and anion redox in Li-rich cathodes by compositional design, so as to realize the regulation of voltage. Furthermore, when the as-prepared high Ni content electrode assembled with Si/C anode into a full-cell, impressive operating voltage (~3.70 V) and long cycle life (72.29% capacity retention after 200 cycles at 1C) can be achieved. Our work provides an efficient and up-scalable strategy for the preparation of electrodes with high voltage and high useful energy density, and making them a rather promising cathode candidate for Li ion batteries.