Polypyrrole-based carbon-coated SnO₂/PCNF electrodes

Tin oxide (SnO₂) shows great promise as an anode material due to its high capacity and ample supply. However, SnO₂ anodes face challenges including aggregation, low conductivity, and significant volume changes during cycling, which lead to powdering of active ingredients and breaking of the solid electrolyte interphase (SEI), ultimately impairing energy transfer and cycling stability. Carbon materials offer several advantages in this context, such as amorphous structures, large interlayer distances, high electrical conductivity, and excellent ion transport abilities. In addition, carbon can function as a buffer within the electrodes, suppressing volume fluctuations and preventing structural distortions (pulverization/agglomeration) caused by the volume change. They also alleviate side reactions at the interface by precluding direct contact between the active material and the electrolyte, thereby enhancing the electrochemical performance of batteries. A simple and rapid method was introduced to synthesize high-performance polyacrylonitrile-based, binder-free N-doped carbon-coated SnO₂/porous carbon nanofibers (PCNFs) using centrifugal spinning and polypyrrole (PPy)-based amorphous carbon coating and these were then used as anodes in lithium-ion and sodium-ion batteries for the first time. The resulting N-doped carbon-coated SnO₂ incorporated into porous carbon nanofibers (N-C@ SnO₂/PCNFs) exhibited a high initial discharge capacity of 1200 mAh g⁻¹ for lithium-ion batteries and 680 mAh g⁻¹ for sodium-ion batteries, as well as excellent durability during cycling even after 200 cycles. The 3D CNF matrix effectively buffered the volume changes and enhanced structural stability by suppressing particle aggregation during the charge/discharge process. Furthermore, the second carbon coating not only prevented direct contact between the active material and the electrolyte but also increased electronic conductivity. Results showed that PPy-based carbon coating is an effective strategy for synthesizing high-performance electrodes in energy storage systems.