Feasible constructions of Bi@CNT materials with extremely high rate and Na+ storage performance

Abstract

Micro-sized Bi is well-known for its high capacity and optimal operating potential, which makes it a compelling option for the negative electrodes of SIBs. To maximize the sodium storage capacity of Bi, developing its advantages and mitigating its disadvantages during storage processes are pivotal considerations. Our studies innovatively synthesized Bi@CNT materials constructed from micro-sized Bi and carbon nanotubes (CNTs). Moreover, it is intriguingly found that some nano-sized Bi particles are embedded on the surface of the CNTs and inserted into the CNTs. These unique structures enable Bi@CNT to possess excellent Na⁺ energy storage capacity and rate performance. At a current density of 0.2 A g⁻¹, the maximal reversible capacity of Bi@CNT-2.61 is 462 mA h g⁻¹, which surpasses the theoretical specific capacity of pure Bi. Surprisingly, the discharge-specific capacity of Bi@CNT-2.61, with a mass loading of 0.89 mg cm⁻², is maintained at 248.1 mA h g⁻¹ after 5450 cycles at an enormously high current density of 50 A g⁻¹. When full cells (Bi@CNT-2.61//NVP) are assembled with Na₃V₂(PO₄)₃ (NVP) as the cathode and Bi@CNT-2.61 as the anode, it is found that the Bi@CNT-2.61//NVP demonstrates a high energy density of 192.1 W h kg⁻¹. The high capacity retentions of the Bi@CNT-2.61//NVP are 96.67% and 98.64% after 445 and 400 cycles at current densities of 1.0 and 5.0 A g⁻¹, respectively. The exceptional stability and charge transport of Bi@CNTs were analyzed in detail by ex situ XRD measurements and DFT computations.