Spinel-Layered Intergrowth Composite Cathodes for Sodium-Ion Batteries

The vital challenge of a layered manganese oxide cathode for sodium-ion batteries is its severe capacity degradation and sluggish ion diffusion kinetics caused by irreversible phase transitions. In response to this problem, the spinel-layered manganese-based composite with an intergrowth structure is ingeniously designed by virtue of an interesting spinel-to-layered transformation in the delithiated LiMn₂O₄ under Na⁺ insertion. This unique spinel-layered intergrowth structure is strongly confirmed by combining multiple structure analysis techniques. The layered component can provide more reversible capacity, while the spinel component is crucial for the stabilized crystal structure and accelerated ion diffusion kinetics. As an appealing cathode for sodium-ion batteries, the layered-spinel composite delivers a high reversible capacity of 180.9 mAh g^-1, excellent cycling stability, and superior rate capability with 55.7 mAh g^-1 at 12 C. Furthermore, the reaction mechanism upon Na⁺ extraction/insertion is revealed in detail by ex situ X-ray diffraction and X-ray photoelectron spectroscopy, indicating that Na⁺ ions can be accommodated by the layered structure at a low voltage and by the spinel at a high voltage. This study will provide a new idea for the rational design of an advanced cathode for sodium-ion batteries.

O3-Type Layered Ni-Rich Oxide: A High-Capacity and Superior-Rate Cathode for Sodium-Ion Batteries

Inspired by its high-active and open layered framework for fast Li⁺ extraction/insertion reactions, layered Ni-rich oxide is proposed as an outstanding Na-intercalated cathode for high-performance sodium-ion batteries. An O3-type Na_0.75 Ni_0.82 Co_0.12 Mn_0.06 O₂ is achieved through a facile electrochemical ion-exchange strategy in which Li⁺ ions are first extracted from the LiNi_0.82 Co_0.12 Mn_0.06 O₂ cathode and Na⁺ ions are then inserted into a layered oxide framework. Furthermore, the reaction mechanism of layered Ni-rich oxide during Na⁺ extraction/insertion is investigated in detail by combining ex situ X-ray diffraction, X-ray photoelectron spectroscopy, and electron energy loss spectroscopy. As an excellent cathode for Na-ion batteries, O3-type Na_0.75 Ni_0.82 Co_0.12 Mn_0.06 O₂ delivers a high reversible capacity of 171 mAh g^-1 and a remarkably stable discharge voltage of 2.8 V during long-term cycling. In addition, the fast Na⁺ transport in the cathode enables high rate capability with 89 mAh g^-1 at 9 C. The as-prepared Ni-rich oxide cathode is expected to significantly break through the limited performance of current sodium-ion batteries.