Revealing the Effect of Ti Doping on Significantly Enhancing Cyclic Performance at a High Cutoff Voltage for Ni-Rich LiNi_0.8Co_0.15Al_0.05O₂ Cathode

Abstract

As a kind of Ni-rich cathode material, LiNi0.8Co0.15Al0.05O2 undergoes severe phase transition when cycling under a high cutoff voltage, causing a sharp decline in reversible capacity. In this study, we synthesize LiNi0.8Co0.15Al0.05O2 with a range of Ti doping contents through a facile solid state approach. When the doping content is 1 mol %, it can still deliver a discharge capacity of 179.6 mAh g–1 after 200 cycles at 3.0–4.5 V, with a capacity retention of 97.4%, in comparison with 167.3 mAh g–1 and 89.2%, respectively, for pristine LiNi0.8Co0.15Al0.05O2. Various morphological and structural characterizations are performed to thoroughly comprehend the excellent cyclic performance of Ti-doped LiNi0.8Co0.15Al0.05O2. High resolution transmission electron microscopy images in combination with powder X-ray diffraction patterns illustrate that Ti dopant effectively suppresses the undesirable phase transition. Electrochemical impedance spectroscopy results confirm a relatively low increase of charge transfer impedance, and differential capacity versus voltage curves show a more moderate polarization during cycling. When LiNi0.8Co0.15Al0.05O2 cycles under a high cutoff voltage, the appropriate amount of Ti doping plays a role in stabilizing the structure and relieving the surface deterioration, which proves to be the key to the extremely superior cyclic performance even at 4.5 V.