Titanium and fluorine co-modification strengthens high-voltage electrochemical performance of LiCoO₂

The cathode material for lithium-ion batteries, LiCoO2 (LCO), is suffered from the structural damage and rapid performance degradation at high voltage. In this article, a hydrolysis-calcination method was explored to modify the single-crystal LCO particles with Ti&F co-modification, aiming at strengthening the structural stability through decreasing the energy barrier of lithium ion diffusion. Evaluated at high voltage (3.0-4.55 V), the optimal sample LCO-TF2 has the initial discharge capacity of 199.3 mAh g(-1) and capacity retention rate of 75% after 100 cycles at 1 C and 45 degrees C, significantly higher than that of the pristine sample (192.8 mAh g(-1) and 35%). Characterized by XRD, TEM, XPS, etc., it is illustrated that the Ti&F co-modified sample LCO-TF2 has the rock-salt phase on its surface besides the layered structure inside. GITT results indicate that Li+ diffusion coefficients of LCO-TF2 are more than twice times of those of LCO under the voltage range of 4.0-4.55 V. The in-situ XRD tests reflect that during the charge-discharge cycle the crystal structure variation of LCO-TF2 is suppressed during Li+ extraction and insertion. Further, DFT calculations disclose that with the co-modification of Ti and F the surface film of LiCoO2 possesses lower energy barrier of Li-ion diffusion. These results would provide useful guidance on improving electrochemical performance of LiCoO2 at high cut-off voltage. (C) 2022 Elsevier B.V. All rights reserved.