Al 2 O 3 -coated LiNi 0.8 Co 0.15 Al 0.05 O 2 /graphene composite as a high-performance cathode material for lithium-ion battery

Abstract

A cathode material composite containing Al₂O₃-coated LiNi_0.8Co_0.15Al_0.05O₂ (NCA) and graphene was prepared via a combination of ultrasonication and mechanical ball milling. No changes were observed in the crystalline structure of this material relative to the bare and Al₂O₃-coated LiNi_0.8Co_0.15Al_0.05O₂ materials based on the XRD spectrum. SEM images indicated that graphene was well distributed between the active material particles. The composite material was compared with the bare and Al₂O₃-coated active materials by electrochemical tests to evaluate its performance in the lithium-ion battery. The resistance values of the solid-electrolyte interphase layer and charge transfer were investigated during cycling by electrochemical impedance spectroscopy. The composite material provided the lowest resistance values with high stability during cycling. The capacity retention of the composite material was 27.7% more in comparison to the bare material during 50 cycles of charge/discharge at a 0.5C rate. Remarkably, the rate capability was improved by using the composite material, with a specific capacity of over 130.9 mAh g^–1 at a 3C rate, which means delivering 62.9 mAh g^–1 more capacity than the bare NCA. Graphene improved capacity retention and rate capability through the creation of a protective layer on the particles and providing a conductive medium in the electrode structure.