Synthesis and electrochemical properties of cation‐disordered rock‐salt x Li 3 NbO 4 ·(1 − x ) NiO compounds for Li‐ion batteries

Summary In this study, Li‐excess cation‐disordered rock‐salt cathode materials, x Li 3 NbO 4 ·(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 d V /d Q 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 − .