In this work, we report a novel design of mixed P2 + T phase NaxCo0.1Mn0.9O2 (0.44 ≤ x ≤ 0.7) with interface rich characteristics for high performance sodium storage, whereby the tunneled T phase offers fast Na ion diffusivity and excellent structural stability, the layered P2 phase contributes to high specific capacity, and the P2 + T phase interface offers additional channels and active sites for charge transfer and excess charge storage. Consequently, the as-prepared NaxCo0.1Mn0.9O2 (0.44 ≤ x ≤ 0.7) demonstrates an excellent discharge capacity of 219 mA h g−1 at a current rate of 0.1C (1C = 176 mA g−1), and retains 117 mA h g−1 even at a high rate of 5C. This outstanding performance is significantly superior to that of pure T-type Na0.44Co0.1Mn0.9O2 and P2-type Na0.7Co0.1Mn0.9O2, and also outperforms state-of-the-art manganese-based cathodes. The kinetic analysis indicates the drastically improved Na+ diffusion coefficient of the P2 + T phase, which is 6 and 200 times that of the pure T and P phases, respectively. The good reversibility and structural stability is evidenced through an ex situ XRD study.
Shilin Zhou,Rui Jiang,Shige Wang,Lu Yu,Xiaoyan Shi,Lianyi Shao,Zhipeng Sun,Lifeng Hang
Metal selenides have aroused significant attention in the realm of efficient ion storage attributed to their exceptional chemical and physical properties, whereas their utilization in sodium-ion batteries (SIBs) is hindered by poor rate performance and cycle stability that originated from their substantial volume expansion throughout Na+ insertion/extraction procedures. This work proposes a productive approach to preserve the structure of the FeSe2 anode via in situ coating nitrogen-doped carbon (NC). The powerful interfacial interaction between FeSe2 micro-nanorods and NC facilitates fast Na+/e− transport kinetics and ensures excellent structural stability of FeSe2@NC. Consequently, FeSe2@NC exhibits a capacity of 379.2 mA h g−1 at a high current density of 10 A g−1 and up to 100% reversible capacity over 1000 cycles at 5 A g−1. Furthermore, the invertible Na+ storage mechanism of FeSe2@NC is investigated by ex situ methods. When FeSe2@NC is used as the anode and Na3V2(PO4)2F3@reduced graphene oxide is used as the cathode to assemble a full battery, it also exhibits a capacity of 167.2 mA h g−1 even after 1000 cycles at 1 A g−1. These exemplary results underscore the potential application value of FeSe2@NC in fast-charging SIBs.
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