Li2TiO3 Dopant and Phosphate Coating Improve the Electrochemical Performance of LiCoO2 at 3.0–4.6 V

Abstract

A sol–gel tandem with a solid-phase modification procedure was developed to synthesize Li2TiO3-doped LiCoO2 together with phosphate coatings (denoted as LCO-Ti/P), which possesses excellent high-voltage performance in the range of 3.0–4.6 V. The characterizations of X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy illustrated that the modified sample LCO-Ti/P had the dopant of monoclinic Li2TiO3 and amorphous Li3PO4 coating layers. LCO-Ti/P has an initial discharge capacity of 211.6 mAh/g at 0.1 C and a retention of 85.7% after 100 cycles at 1 C and 25 ± 1 °C between 3.0 and 4.6 V. Nyquist plots reflect that the charge transfer resistance of LCO-Ti/P after 100 cycles at 1 C is much lower than that of the spent LCO, which benefits Li-ion diffusion. Density functional theory calculations disclose the superior lattice-matching property of major crystal planes for Li2TiO3 and LiCoO2, the lower energy barriers for Li-ion diffusion in Li2TiO3, and the suppressed oxygen release performance resulting from phosphate adsorption. This work provides useful guidance on the rational design of the high-voltage performance of modified LiCoO2 materials in terms of lattice-matching properties aside from the phosphate coating to reduce the energy barriers of Li-ion diffusion and enhance cycling stability.