One-dimensional coaxial cable-like MWCNTs/Sn4P3@C as an anode material with long-term durability for lithium ion batteries

Abstract

High capacity Sn₄P₃ is considered as a promising anode candidate for lithium-ion batteries (LIBs), but the fast capacity decay caused by the enormous volume changes and tin agglomeration during cycling largely limits its practical applications. Herein, MWCNTs/Sn₄P₃@C with a coaxial cable-like structure is designed, where a carbon protective layer is wrapped on the surfaces of Sn₄P₃ nanoparticles to minimize their exposure to the electrolyte and multi-walled carbon nanotubes (MWCNTs) serve as a conductive backbone to disperse Sn₄P₃ nanoparticles. When applied as the lithium container, the MWCNTs/Sn₄P₃@C composites demonstrate excellent cycling stability (delivering a high reversible capacity of 768.8 mA h g⁻¹ after 100 cycles at 100 mA g⁻¹ and 569.5 mA h g⁻¹ after 1000 cycles at 1000 mA g⁻¹) and rate capability (a de-lithiation capacity of 520.1 mA h g⁻¹ maintained at a high current density of 2000 mA g⁻¹). Furthermore, full cells composed of the MWCNTs/Sn₄P₃@C anode and the commercially available LiNi_1/3Mn_1/3Co_1/3O₂ cathode were also assembled. The result of cycling performance showed a reversible capacity of 507 mA h g⁻¹ after 100 cycles, which is far superior to that of bare Sn₄P₃ and MWCNTs/Sn₄P₃ anodes with the reversible capacity lower than 100 mA h g⁻¹. These excellent electrochemical performances originate from a synergistic effect between the MWCNT conductive backbone and carbon shell protective layer. The MWCNT backbone can enhance the conductivity and serve as a framework to disperse Sn₄P₃ nanoparticles, thus helping to accommodate the large volume changes during cycling, while the carbon shell not only can further enhance the conductivity but also minimize the side reaction between Sn₄P₃ nanoparticles and electrolytes.