Dopamine-derived N-doped carbon encapsulating hollow Sn4P3 microspheres as anode materials with superior sodium storage performance

Abstract

Sn4P3 is one of the most promising anode materials for sodium ion batteries (SIBs) owning to the alloying reaction of P and Sn with Na to form Na3P and Na15Sn4, which is beneficial to achieve a high specific capacity, especially for the high volumetric capacity (6650 mAh cm−3). However, the high capacities generate large volume changes, which pulverize the anode material, resulting in poor cycling stability. This restricts its practical applications for SIBs. Here, the dopamine-derived N-doped carbon encapsulating hollow Sn4P3 microspheres (hollow Sn4P3@C) composites are prepared by an in-situ self-polymerization of dopamine on the surface of hollow SnO2 microspheres followed by a carbonization process and a low temperature phosphorization using NaH2PO2 as P source. The results of the structural and morphological characterization can be demonstrated that as-prepared hollow Sn4P3@C composites are constructed by hollow Sn4P3 microspheres with the ultrathin N-doped carbon coating. The as-prepared samples are tested as the anode materials for SIBs. Compared with bared hollow Sn4P3 microspheres, hollow Sn4P3@C composites exhibit better electrochemical sodium storage performance. As a result, hollow Sn4P3@C composites deliver the first discharge and charge specific capacities of 840 and 587 mAh g−1 with a high initial coulombic efficiency of 70% at a current density of 0.2 A g−1. Moreover, hollow Sn4P3@C composites display superior rate capabilities of 555, 438, 339, 239, 157 and 92 mAh g−1 at 0.2 A g−1, 0.5 A g−1, 1 A g−1, 2 A g−1, 5 A g−1 and 10 A g−1, respectively. Meanwhile, hollow Sn4P3@C composites show a high discharge capacity of 372 mAh g−1 at 0.2 A g−1 after long 200 cycles. A detailed electrochemical kinetic analysis indicates that energy storage for Na+ in Sn4P3 is due to a pseudocapacitive mechanism. The good electrochemical sodium storage performance of as-prepared hollow Sn4P3@C composites may be attributed to the introduction of N-doped carbon coating and unique hollow structure. Therefore, our work provides a new structure model for the development of new anode materials for SIBs.