Toward emerging two-dimensional nickel-based materials for electrochemical energy storage: Progress and perspectives

Two-dimensional (2D) Ni-based materials have attracted considerable attention due to their distinctive prop-erties, including high electro-activity, large specific surface areas, controllable chemical compositions, and abundant forms of composite materials. Over the last decade, there has been increasing research interest in constructing advanced 2D Ni-based nanomaterials possessing short and open channels with efficient mass diffusion capability and rich accessible active sites for electrochemical energy storage (EES). Herein, the recent advances in developing emerging 2D Ni-based materials involving Ni-based oxides, sulfides, phosphides, sele-nides, hydroxides, metal-organic frameworks (MOFs), and Ni-rich layered oxides (LiNixMyM & PRIME;zO2/NaNixMyM & PRIME;zO2) for EES is reviewed. After a brief summary of crystal structures and synthetic methods of 2D Ni-based materials, design strategies for improving electrochemical performances of 2D Ni-based materials are described in detail through vacancy creation, heteroatoms doping, and 3D nanostructures. Afterward, their applications as electrode materials for EES including supercapacitors, alkali (Li, Na, K)-ion batteries, and multivalent metal (Zn, Mg, Ca) -ion batteries are discussed. This review also discusses the charge storage mechanisms of 2D Ni-based materials by various advanced characterization methods. Finally, the current challenges and research outlook of 2D Ni-based materials toward high performance EES devices are presented.