Facilitating Layered Oxide Cathodes Based on Orbital Hybridization for Sodium‐Ion Batteries: Marvelous Air Stability, Controllable High Voltage, and Anion Redox Chemistry

Abstract

Layered oxides have become the research focus of cathode materials for sodium‐ion batteries (SIBs) due to the low cost, simple synthesis process, and high specific capacity. However, the poor air stability, unsteady phase structure under high voltage, and slow anionic redox kinetics hinder their commercial application. In recent years, the concept of manipulating orbital hybridization has been proposed to simultaneously tune the microelectronic structure and modify the surface chemistry environment intrinsically. In this review, the hybridization modes between atoms in 3d/4d transition metal (TM) orbitals and O 2p orbitals near the region of the Fermi energy level (EF) were summarized based on orbital hybridization theory and first‐principles calculations as well as various sophisticated characterizations. Furthermore, the underlying mechanisms are explored from macro‐scale to micro‐scale, including enhancing air stability, modulating high voltage, and stabilizing anionic redox chemistry. Meanwhile, the origin, formation conditions, and different types of orbital hybridization, as well as its application in layered oxide cathodes are presented, which provide insights into the design and preparation of cathode materials. Ultimately, the main challenges in the development of orbital hybridization and its potential for the production application are also discussed, pointing out the route for high‐performance practical sodium layered oxide cathodes.This article is protected by copyright. All rights reserved

Routes to high-performance layered oxide cathodes for sodium-ion batteries

“…3c). 84,85 Similar to Li x TMO 2 for LIBs, Na x TMO 2 has also emerged as one of the most efficient cathodes for SIBs. [86][87][88][89] A variety of transition metals can be applied in the preparation of cathodes, but not all of them exhibit satisfactory properties.…”

Manipulating Local Chemistry and Coherent Structures for High-Rate and Long-Life Sodium-Ion Battery Cathodes

“…Among various cathode candidates, layered transition-metal oxides Na x TMO 2 (0 < x ≤ 1, TM stands for transition-metal elements, including Ti, V, Cr, Mn, Fe, Co, Ni, etc.) have garnered considerable attention, owing to their distinctive traits of versatile compositional flexibility, high capacity, and environmental friendliness …”

Predominant P3-Type Solid–Solution Phase Transition Enables High-Stability O3-Type Na-Ion Cathodes

“…However, the increasing demand and uneven distribution of Li resources hinder the extensive application of LIBs in the field of energy storage, in which cost is the most important factor. Na-ion batteries (SIBs) are expected to be an alternative to LIBs in energy storage systems because of the stable supply and even distribution of Na resources. − In the current SIBs, cathode materials play a significant role in energy density, cycling life, and rate property. , Therefore, an in-depth investigation into cathode materials and their corresponding reaction mechanisms during (de)­sodiation is of great importance for both the engineering and scientific point of view. − Among the reported cathode materials, Na-ion layered transition metal oxides (Na x TMO 2 ) have gained significant attention owing to their great compositional diversity, relatively easy preparation process, and highly reversible specific capacity. − O3-type and P2-type Na x TMO 2 are the widely studied layered structures used for cathode materials, which are composed of TMO 6 octahedra sheets, where Na ions occupy the octahedral (O) and prismatic environment (P) sites between the octahedra sheets, respectively. The figure (e.g., 3 in O3) represents the stacking number of TMO 6 octahedra sheets in a structure cell .…”