Bi/C nanosheet microspheres with an open pore structure as anodes for sodium ion batteries with high capacity, excellent rate performance and long cycle life

Abstract

To develop high-performance and low-cost anode materials for sodium ion batteries, novel Bi/C nanosheet microspheres with an open pore structure (labeled as ops-Bi/C nanosheet microspheres), in which nanosheets are assembled from Bi nanospheres and disordered C, are synthesized through facile methods using Bi(NO₃)₃, glucose and ethylene glycol as raw materials. Benefiting from the synergy of the material's unique microstructure, carbon coating and NaPF₆–diglyme electrolyte, the ops-Bi/C nanosheet microspheres exhibit a higher stable reversible capacity (∼400 mA h g⁻¹ at 0.1 A g⁻¹) than the theoretical capacity of Bi metal, excellent rate performance (396, 393, 395, 392 and 381 mA h g⁻¹ at 0.2, 1, 5, 10 and 20 A g⁻¹, respectively) and long cycle life (361 mA h g⁻¹ after 10 000 cycles at 5 A g⁻¹). Moreover, even if the mass loading of the ops-Bi/C nanosheet microspheres exceeds 10 mg cm⁻², the electrode still shows a high reversible capacity of 321 mA h g⁻¹ at 0.8 A g⁻¹ with good cycle performance. The sodium ion full cells composed of the ops-Bi/C nanosheet microsphere anode and commercial Na₃V₂(PO₄)₃ (NVP) cathode exhibit high energy density (174 W h kg⁻¹_(total) at 0.1 A g⁻¹_(NVP)) and long cycle performance (600 cycles at 1 A g⁻¹_(NVP)).