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

Abstract

Layered sodium transition-metal oxides, Na_xMeO₂, 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 Na_0.5[Ni_0.2Co_0.15Mn_0.65]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/Na_0.5[Ni_0.2Co_0.15Mn_0.65]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.