Bismuth Incorporation Induced Low-Frequency Phonon Enhancing the Kinetics and Stability of Cathodes for Sodium-Ion...

Rapid capacity fading, along with severe challenges in the fast-charging process, such as anomalous migration of transition metals (TMs) in-plane and out-of-plane, lattice stress, and microcrack formation, leads to poor cycle performance, which seriously hinders the commercial applications of layered cathodes. Herein, heavy atom bismuth (Bi) is utilized as a robust dopant for O3-NaNi_0.28Cu_0.05Fe_0.33Mn_0.33O₂ to achieve the purpose of decreasing the atoms' vibration frequency and lattice scattering, accelerating Na⁺ transfer kinetics. Specially, the Bi incorporation is working as not only a "solubilizer" that improves Cu doping dose, but also a "riveted joint" that restrains the blocking of Na⁺ transfer and the gliding of TMs into Na-O layers. Besides, the densification of the electrode is achieved by introducing Bi. The gaps and the cracks between the grain boundary are effectively suppressed, owing to the reduced lattice internal stress. Consequently, the as-synthesized NaNi_0.28Fe_0.31Cu_0.05Bi_0.02Mn_0.33O₂ exhibits impressive rate capability 75.5 mAh g^-1 at 20 C and excellent cycle stability with 90.58% capacity retention after 200 cycles at the current density of 0.2C. The impressive electrochemical performance is benefited from the low-frequency phonon scattering caused by the Bi-atom. This work provides a new idea for the design of ultra-long-life and fast-charging sodium-ion batteries.