Synthesis of SnO₂: Versus Sn crystals within N-doped porous carbon nanofibers via electrospinning towards high-performance lithium ion batteries

The design of tin-based anode materials (SnO₂ or Sn) has become a major concern for lithium ion batteries (LIBs) owing to their different inherent characteristics. Herein, particulate SnO₂ or Sn crystals coupled with porous N-doped carbon nanofibers (denoted as SnO₂/PCNFs and Sn/PCNFs, respectively) are fabricated via the electrospinning method. The electrochemical behaviors of both SnO₂/PCNFs and Sn/PCNFs are systematically investigated as anodes for LIBs. When coupled with porous carbon nanofibers, both SnO₂ nanoparticles and Sn micro/nanoparticles display superior cycling and rate performances. SnO₂/PCNFs and Sn/PCNFs deliver discharge capacities of 998 and 710 mA h g^-1 after 140 cycles (at 100, 200, 500 and 1000 mA g^-1 each for 10 cycles and then 100 cycles at 100 mA g^-1), respectively. However, the Sn/PCNF electrodes show better cycling stability at higher current densities, delivering higher discharge capacities of 700 and 550 mA h g^-1 than that of SnO₂/PCNFs (685 and 424 mA h g^-1) after 160 cycles at 200 and 500 mA g^-1, respectively. The different superior electrochemical performance is attributed to the introduction of porous N-doped carbon nanofibers and their self-constructed networks, which, on the one hand, greatly decrease the charge-transfer resistance due to the high conductivity of N-doped carbon fibers; on the other hand, the porous carbon nanofibers with numerous voids and flexible one-dimensional (1D) structures efficiently alleviate the volume changes of SnO₂ and Sn during the Li-Sn alloying-dealloying processes. Moreover, the discussion of the electrochemical behaviors of SnO₂vs. Sn would provide new insights into the design of tin-based anode materials for practical applications, and the current strategy demonstrates great potential in the rational design of metallic tin-based anode materials.