In this study, Li-excess cation-disordered rock-salt cathode materials, xLi 3 NbO 4 Á(1 − x) NiO (LNNO, 0.55 ≤ x ≤ 0.7), are synthesized to explore the effect of composition on the structure and electrochemical performance using a sol-gel method for the first time. X-ray diffraction results combined with Rietveld refinements demonstrate that pure cation-disordered rock-salt structure can be obtained at x ≥ 0.6. The electron microscopy results of samples demonstrate the irregular particles with size of 1 to 10 μm and rock-salt structure is further confirmed. The samples with x = 0.6, 0.65, and 0.7, respectively, exhibit the much higher reversible capacity than their theoretical Ni 2+ /Ni 3+ capacity attributing to anionic redox reaction. The LNNO6 sample deliver the first discharge capacity 155.35 mAh/g and 82.9% capacity retention after 40 cycles. In addition, X-ray photoelectron spectroscopy analyses and dV/dQ measurements are utilized to investigate the restricted electrochemical behaviors and performances which are constrained by the competition between Ni 2+ /Ni 3+ and O 2− /O −. K E Y W O R D S cation-disordered, electrochemical performance, lithium ion battery, Li 3 NbO 4-based rock-salt structure 1 | INTRODUCTION With the advantages of low pollution, high energy density, and long cycle life, lithium-ion batteries have become the most popular rechargeable batteries in portable electronics and vehicles. 1-5 To solve the crisis of energy resource and environmental pollution, some promising materials, such as transition metal (TM) oxides, metal-organic frameworks (MOFs), and Si-based materials are designed for the areas of lithium batteries, catalysis, supercapacitor, and optical devices. 6-16 Therefore, aiming at the application of Li-ion batteries for advanced energy powers, researchers around the world have paid a lot of efforts to develop cathode materials, especially the ordered TM oxides, such as LiMO 2 and Li 1 + x M 1 − x O 2 (M = Mn, Ni, Co, etc.). 17-19 It was generally accepted in the past several decades that wellordered structure between Li and the TM sublattice is good for Li diffusion and then improve the electrochemical performance effectively. However, most of layered cathode materials suffer from instability and oxygen release in the charging process as the result of cations mixing and phase change. Recently, cation-disordered materials have attracted more attention because of unique lithium migration