A review of Ni-based layered oxide cathode materials for alkali-ion batteries

Compared with the costly and toxic LiCoO₂ cathode in lithium-ion batteries (LIBs), nickel-based layered oxide (NLO) cathode materials exhibit the advantages of high capacity, natural abundance, environment-friendliness, and low cost, displaying tremendous application potentials in power batteries for automobiles and aircrafts. This review comprehensively introduces the challenges faced by NLO cathode materials in all alkali-ion batteries (AIBs) in their material synthesis, cation mixing, particle cracking, phase changes, cation dissolution of Mn, and oxygen loss Various strategies, including heteroatom doping, surface coating, and concentration gradient, are applied to tackle these problems by developing layered LiNi_1-MO₂ (M: metal; 0 < x < 1) and LiNiCoMnO₂ (x + y + z = 1) materials. The successful commercial application of NLO cathode materials in LIBs has further driven their developments in sodium/potassium-ion batteries via the synthesis of (Na/K)Ni_1-MO₂. Moreover, many sophisticated techniques, including in situ X-ray diffraction, scanning/transmission electron microscopy, operando neutron diffraction, and elemental analysis, are used to simultaneously monitor real-time phase changes, lattice variations, structural distortions, and elemental dissolutions of NLO-based materials. Furthermore, density functional theory (DFT) calculations are discussed as a powerful tool for predicting structural evolution, energy band structures, optimal doping concentrations, and ion diffusion pathways, thereby guiding the reasonable design of these materials. Finally, this review provides perspectives on future research directions and modification strategies for NLO cathode materials in AIBs, aiming to accelerate their deployment in electric vehicles and other energy storage devices. These efforts are expected to contribute significantly to the advancement of sustainable energy technologies and the global pursuit for carbon neutrality.