Tailoring Na+ Diffusion Kinetics and Structural Stability of P2-Layered Material by W-Lattice Doping†

Abstract

The pursuit of advanced sodium-ion batteries (SIBs) has been intensified due to the escalating demand for sustainable energy storage solutions. A W-doped P2-type layered cathode material, Na_0.67Ni_0.246W_0.004Mn_0.75O₂ (NNWMO), has been developed to address the limitations of traditional cathode materials. Compared to the pristine Na_0.67Ni_0.25Mn_0.75O₂ (NNMO), NNWMO exhibits improved reversible capacity, excellent cycle performance, and remarkable rate performance. It can deliver an increased discharge capacity of 142.20 mAh/g at 0.1 C, with an admirable capacity retention of 80.5% after 100 cycles at high voltage. In situ XRD results demonstrate that the rivet effect related to the strong W—O bonds inhibits irreversible phase transition and enhances structural reversibility during charge/discharge processes. High-resolution scanning transmission electron microscopy and X-ray diffraction results confirm successful lattice doping of W⁶⁺ and increased layer spacing, contributing to favorable sodium ion diffusion kinetics. Density-functional theory (DFT) calculation results further reveal that the smoother Na⁺ ion diffusion dynamics is attributed to the reduced migration energy barrier of Na⁺ with the insertion of W⁶⁺. This study provides valuable insights into the design of high-performance cathode materials for next-generation SIBs, showcasing the potential for more efficient, stable, and enduring energy storage solutions.