High-rate, long cycle-life Li-ion battery anodes enabled by ultrasmall tin-based nanoparticles encapsulation

Tin (Sn)-based materials are potential alternatives to the commercial graphite anode for next generation Li-ion batteries, but their successful application is always impeded by fast capacity fading upon cycling that stemmed from huge volume variations during lithiation and delithiation. We develop an applicable strategy of encapsulating sub-10-nm-sized Sn-based nanoparticles (i.e., Sn and SnO₂) in nitrogen/phosphorus codoped hierarchically porous carbon (NPHPC) or NPHPC-reduced graphene oxide hybrid (NPHPC-G) to effectively solve the issues of Sn-based anodes. Benefiting from the peculiar structure, the composites exhibit unprecedented electrochemical behaviors, for example, NPHPC-G@Sn and NPHPC-G@SnO₂ deliver a high reversible capacity of ~1158 and ~1366 mAh g^-1 at 200 mA g^-1, respectively, and maintain at ~1099 mAh g^-1 after 500 cycles and ~1117 mAh g^-1 after 300 cycles. In situ transmission electron microscopy and ex situ scanning electron microscopy observations unveil that these composites are able to withstand the volume changes of Sn-based nanoparticles while sustaining the framework of the architectures and hence conferring outstanding electrochemical properties. Our present work provides both in situ and ex situ techniques for understanding the so-called synergistic effect between metals or metal oxides and carbons, which may offer rational guidance to design carbon-based functional materials for energy storage.