Suppressing Surface Ligand-to-Metal Charge Transfer toward Stable High-Voltage LiCoO2.

ABSTRACT

Increasing the charging cutoff voltage is a viable approach to push the energy density limits of LiCoO2 and meet the requirements of the rapid development of 3C electronics. However, an irreversible oxygen redox is readily triggered by the high charging voltage, which severely restricts practical applications of high-voltage LiCoO2. In this study, we propose a modification strategy via suppressing surface ligand-to-metal charge transfer to inhibit the oxygen redox-induced structure instability. A d0 electronic structure Zr4+ is selected as the charge transfer insulator and successfully doped into the surface lattice of LiCoO2. Using a combination of theoretical calculations, ex situ X-ray absorption spectra, and in situ differential electrochemical mass spectrometry analysis, our results show that the modified LiCoO2 exhibits suppressed oxygen redox activity and stable redox electrochemistry. As a result, it demonstrates a robust long-cycle lattice structure with a practically eliminated voltage decay (0.17 mV/cycle) and an excellent capacity retention of 89.4% after 100 cycles at 4.6 V. More broadly, this work provides a new perspective on suppressing the oxygen redox activity through modulating surface ligand-to-metal charge transfer for achieving a stable high-voltage ion storage structure.