Sodium-ion batteries (SIBs) have attracted much scientific interest for use in large-scale energy storage systems because sodium is cheaper than lithium. However, the large radius of Na+ and barriers to Na+ transport result in sluggish kinetics and complicated structural distortion, leading to unsatisfactory rate capability and poor cycling stability. It therefore is essential to develop an electrode with enhanced kinetics and a stable structure during cycling to improve SIB performance. Among the various layered oxide cathodes, those with a spinel-like structure could play an important role in boosting electron transport because of their excellent intrinsic conductivity, including by coordinating with Na+ insertion/extraction. Moreover, thanks to the inherent high stability of the spinel-like phase, it could function as a stabilizer for host cathode structures. This review summarizes recent advances in spinel engineering on layered oxide cathodes to boost Na+ transport kinetics and provide structural stability to achieve high-performance SIBs, focusing particularly on post-spinel structures, layered oxide integrated spinel-like structures, and spinel transition. The insights proposed in this review will be useful for guiding rational structural engineering and design to drive the development of new materials and chemistries in Na-based electrode materials.

Spinel/Post-spinel engineering on layered oxide cathodes for sodium-ion batteries

Layered Oxide Cathodes Promoted by Structure Modulation Technology for Sodium‐Ion Batteries

3D graphene decorated Na4Fe3(PO4)2(P2O7) microspheres as low-cost and high-performance cathode materials for sodium-ion batteries

Recent advances and prospects of layered transition metal oxide cathodes for sodium-ion batteries

Low-cost layered lithium transition metal oxides delivering high capacity and moderate rate capability are considered as promising cathodes for next-generation lithium-ion batteries (LIBs). However, the low stacking and compressed density results in lower volumetric energy density of such LIBs compared with that of the first commercialized LiCoO2-based battery. Herein, for the first time, a new strategy is rationally proposed to prepare micron-sized monocrystalline LiNi1/3Co1/3Mn1/3O2via stepwise addition of lithium sources into hydroxide/oxide precursors. As anticipated, the as-prepared 4–8 μm-thick monocrystalline cathode exhibits comparable stacking/compressed density with LiCoO2 electrode, achieving ultrahigh volumetric energy density exceeding 2600 W h L−1, enhanced structural stability and high rate capability in half-cells. Moreover, in full-cell configuration, by using this monocrystalline LiNi1/3Co1/3Mn1/3O2 as the cathode and mesocarbon microbeads as the anode, higher volumetric energy density exceeding 660 W h L−1, enhanced cycling stability and high rate capability are achieved, indicating the expectant merits of the micron-sized monocrystalline cathodes. It is also confirmed that this monocrystalline cathode can mitigate side reactions occurring at the electrode/electrolyte interface and maintain the stability of layered structures upon cycling. This facile tactic provides an innovative insight into preparing high-volumetric-energy-density lithium transition metal oxide cathodes with enhanced electrochemical properties. Moreover, this approach can be readily extended to prepare other types of layered and spinel monocrystalline cathodes with improved volumetric energy density.

Micron-sized monocrystalline LiNi1/3Co1/3Mn1/3O2 as high-volumetric-energy-density cathode for lithium-ion batteries

Layered sodium transition-metal oxides, NaxMeO2, with large theoretical capacity are regarded as an important class of cathode materials for sodium-ion batteries (SIBs). However, they usually exhibit inferior thermodynamic stability and sluggish Na+ kinetics due to the unwanted phase transitions and large Na+-ionic radius. In this work, considering the beneficial synergistic effects of layered P2/P3 and Fdm spinel phases, a stable layered/spinel intergrowth nanocomposite Na0.5[Ni0.2Co0.15Mn0.65]O2 is rationally designed and successfully prepared via a co-precipitation route and a subsequent solid-state reaction, and the triphase synergy in this layered/spinel nanocomposite is demonstrated. In Na/Na0.5[Ni0.2Co0.15Mn0.65]O2 half-cells, it delivers a high specific capacity of ∼180 mA h g−1 and a good cycling stability, with a capacity retention of 87.6% after 100 cycles, at a rate of 0.1C between 1.5 and 4.0 V (vs. Na/Na+). The large reversible capacity of 105 mA h g−1 is also achieved even at a high rate of 10C, indicating high-rate capability. Besides, the full-cells using this nanocomposite as the cathode and hard carbon as the anode exhibit long-term cycle-life and high-power properties, indicating the expected merits of layered/spinel mixed phases. The superior sodium storage performance of this layered P3/P2 and spinel intergrowth nanocomposite makes it a promising candidate as a long-life and high-rate cathode for SIBs.

Xianhang Lu

Papers

A stable layered P3/P2 and spinel intergrowth nanocomposite as a long-life and high-rate cathode for sodium-ion batteries