Engineering carbon-nanochain concatenated hollow Sn4P3 nanospheres architectures as ultrastable and high-rate anode materials for sodium ion batteries

Abstract Tin phosphide (Sn4P3) that identified as a potential anode for sodium ion batteries (SIBs) based on its high theoretical specific capacity mostly confronts with the huge challenges in rapid capacity decay, severe volume evolution and weak diffusion kinetics upon cycling. It is of great theoretical and practical significance to develop the multilevel structured metal phosphide anode in high performance SIBs systems. Herein, we construct a nanochain-like architecture built from hollow yolk-shell Sn4P3@C nanospheres (Sn4P3@CNF) by electrospinning method and phosphorization treatment, in which all hollow Sn4P3 nanospheres are uniformly chained to one dimensional (1D) carbon nanofibers, forming a necklace-like hybrid conductive construction. The synergistic effect between hollow Sn4P3 nanospheres and nanochain architecture not only offers unblocked transfer channels for Na+ and accelerates the long-distance electronic transmission, but also guarantees excellent electrode kinetics and accommodates volume expansion. The Sn4P3@CNF electrode delivers a highly reversible discharge capacity of 297.6 mAh g−1 at 1 A g−1 after 1750 cycles, 250.6 mAh g−1 at 2 A g−1 after 4700 cycles, as well as ultrastable cycling durability up to 14000 cycles with a capacity of 157.8 mAh g−1 even at a high rate of 5 A g−1. These results demonstrate the greatest cyclability reported so far on Sn4P3-based anodes for SIBs. Meanwhile, the consecutive CV measurement further confirms a capacitive electrochemical redox behavior of Sn4P3@CNF upon cycling. More interestingly, the Sn4P3@CNF electrode displays the superior cycling stability and rate capability in sodium ion full cells as combined with a high-voltage Na3V2(PO4)3 cathode, where the full cell delivers an initial discharge capacity of 286.4 mAh g−1 and maintains a 67.2% capacity retention after 160 cycles at 1 A g−1, making it a great potential for practical application in SIBs systems.