A novel high-entropy layered cathode with a robust structure and fast dynamics at high rates for Na-ion batteries

Abstract

The unstable anionic redox reactions (ARRs) in high-energy Na layered cathode materials result in sluggish ARR kinetics and inadequate structural stability, ultimately leading to rapid capacity degradation and unfavorable rate capabilities. In this work, a high entropy layered oxide P2-Na_0.66Mn_0.6Li_0.1Ti_0.1(MgAlCuZn)_0.05O₂ (NMLTMACZ), was synthesized using a solid-state reaction method to achieve a stable phase structure. Such a novel NMLTMACZ cathode with O redox exhibits an exceptionally high initial reversible capacity of 245.56 mA h g⁻¹ at 0.05C, with an unsatisfactory capacity retention of ∼58.56% after 100 cycles at 0.1C. However, the P2-NMLTMACZ cathode shows an outstanding rate capacity of 147.18 mA h g⁻¹ and superior cycling stability with ∼84.63% capacity retention after 100 cycles at a high rate of 1C. The significant improvement in high-rate performance can be attributed to the robust structure, fast Na⁺-ion transport, and O-redox dynamics of the NMLTMACZ cathode, as evidenced by electrochemical impedance spectroscopy (EIS), ex situ X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) experiments. This study provides a new perspective on the design of high-capacity cathode materials with highly reversible ARR, demonstrating enhanced high-rate performance through rational lattice modulation.