A novel synthetic strategy towards NaCl-type NixCo1−xO solid solution nanoplatelets encapsulated in N-doped carbon for enhanced lithium-ion storage

Abstract

NaCl-type Ni-Co oxide solid solution is expected to be a promising alternative anode material for lithium-ion batteries. However, the synthesis of solid solutions with well-defined morphology and homogeneity is still challenging. Based on a novel NixCo1−x(OH)(OCH3)@polydopamine intermediate and its topotactic thermolysis, a unique synthetic route towards NixCo1−xO solid solution (0 <x ≤ 0.5) encapsulated in N-doped carbon (NixCo1−xO@N-C) was introduced. NixCo1−x(OH)(OCH3) nanoplatelets were firstly synthesized with a solvothermal method and used as the precursor for a NixCo1−x(OH)(OCH3)@polydopamine intermediate. Thermolytic decomposition of metastable NixCo1−x(OH)(OCH3)@polydopamine results in the formation of NaCl-type NixCo1−xO and conformal carbon coating. The resulting NixCo1−xO@N-C shows a well-defined two-dimensional (2D) platelet-morphology and homogenous elemental distribution. Benefited from a tunable Ni/Co ratio, the lithium-storage performance of NixCo1−xO@N-C can be optimized, thereby achieving a high specific capacity of 949 mA h g−1 at the current density of 0.2 A g−1, a great rate capability (530 mA h g−1 at 2 A g−1), as well as excellent long-term cyclability (563 mA h g−1 at 2 A g−1 after 500 cycles) for Ni1/6Co5/6O@N-C. Such a remarkable performance could be attributed to the synergistic effect of different cations, the 2D nanoplatelet structure, the robust conductive carbon coating, and a high pseudocapacitive contribution.