Interfacial Film Li1.3Al0.3Ti1.7PO4-Coated LiNi0.6Co0.2Mn0.2O2 for the Long Cycle Stability of Lithium-Ion Batteries

As one of the most promising market-oriented cathode materials with a high specific capacity, the LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode material has attracted great interest despite the need to overcome the cyclic capacity of persistent attenuation. Herein, Al3+, Ti4+, and P5+ were precipitated on the surface of Ni0.6Co0.2Mn0.2(OH)2 precursor by a wet chemical method, and then the samples were calcined at high temperature to form a compact Li1.3Al0.3Ti1.7PO4 (LATP) solid electrolyte film on the surface of NCM622. The results of XRD, TEM, and XPS analyses showed that the inner layered structure of the cathode material was intact and that the surface was covered with a solid electrolyte film with a thickness of about 1.55 nm. In order to explore the influence of different amounts of LATP on NCM622, films of 0.2, 0.5, and 0.8 wt % LATP were coated on the NCM622 surface. The EIS diagram shows that the stability of the NCM622 interface increases with the increase of LATP, but when the coating amount reaches 0.8 wt %, its capacity will decrease slightly. The results of the electrochemical performance test show that the capacity retention rate of the modified material with 0.5 wt % LATP is 95.7% after 300 cycles at 1C (corresponding specific capacity is 148.1 mAh g–1), while that of the unmodified cathode material is only 68.1% (corresponding specific capacity is 109.7 mAh g–1). This is mainly due to the excellent ionic conductivity of LATP that not only stabilizes the structure of the material and reduces the resistance of lithium-ion migration but also absorbs the residual lithium elements on the surface of the precursor; this forms a protective layer with excellent performance, insulating the cathode material from the corrosion of the electrolyte. This work provides ideas for follow-up related strategies for the long cycle stability of lithium-ion batteries.