O3/P2 Biphasic Layered Cathode Material for Stable Na-Ion Storage

As a significant branch of cathodes for sodium-ion batteries (SIBs), the O3-type layered oxide usually receives extensive attention due to its high theoretical capacity. Due to the high tetrahedral site energy of Na+ diffusion transition state, the kinetics of the charge and discharge processes is sluggish. When the concentration of Na+ decreases, the transition metal layers undergo relative slip, leading to layer structure rearrangement and interface degradation, which result in a decrease in performance. In this work, we propose a strategy to optimize the above problem by varying the sodium content to prepare biphasic cathode materials. The prepared Na0.85Fe0.22Ni0.33Mn0.45O2 cathode has an O3/P2 biphasic structure. It shows excellent electrochemical performance, with an initial discharge specific capacity of 121.3 mAh g–1 at 0.1 C and a capacity retention rate of 94.9% after 100 cycles at 0.2 C. A small amount of P2 is introduced into the phase structure of the O3 to improve the diffusion kinetics and enhance the cycling stability. Due to the cooperative effect of O3/P2, the phase transition of O3/P2–O3/P3/P2 occurs in the electrochemical process, and the complex phase transition of O3–O’3 is inhibited. This study provides an idea for the preparation of high-performance cathode materials.