Electrochemical stabilities of surface aluminum-doped LiNi0.5Co0.2Mn0.3O2 single crystals under different cutoff voltages

Surface Al-doped LiNi0.5Co0.2Mn0.3O2 (523) single crystals with a diameter of 2–4 μm were synthesized by using Ni-Co-Mn hydroxide precursor and combined with further Al3+ coating/annealing operations. Al contents in the surface and the bulk structures of product particles were about 1.05% and 0.02%, respectively. XPS, XRD, and HRTEM results confirm that the Al element exist as a dopant within the layered structures of 523 surface. Coin cell testing of the as-prepared 523 cathode were taken under different voltage ranges of 3.0–4.3 V, 3.0–4.4 V, and 3.0–4.5 V, with corresponding 100 cycles capacity retentions of 91.2%, 74.0%, and 67.8% at 25 °C, and 43.1%, 40.1%, and 31.6% at 55 °C. The capacity degradation rate was mainly associated with the interfacial structure instabilities of 523 materials under different voltage ranges, which have been investigated by electrochemical impedance spectroscopy (EIS) and XPS.