Ultrafine FeS2 nanocrystals/porous nitrogen-doped carbon hybrid nanospheres encapsulated in three-dimensional graphene for simultaneous efficient lithium and sodium ion storage

Abstract

Exploring advanced electrode materials with simultaneous efficient lithium and sodium ion storage is highly desired but remains a considerable challenge mainly due to the significant difference of lithium and sodium ion sizes. Transition metal sulfides (TMSs) have shown great potential in lithium/sodium ion batteries (LIBs/SIBs), however, they still face the critical issues of poor electrical conductivity, sluggish ion diffusion, huge volume expansion and agglomeration of highly reactive nano-metal products. Herein, we deliberately design a multiple-scale nanostructured and flexible anode by a facile one-step sulfidation strategy, in which ultrafine metal sulfide nanocrystals are isolated and protected by porous nitrogen-doped carbon nanospheres (PNC) and then encapsulated into three-dimensional graphene microsheets (3DG). It can effectively eliminate the above issues of TMSs, which makes them a very promising candidate for both LIBs and SIBs for the first time. Thus, the resultant FeS₂/PNC@3DG anode delivers ultrahigh reversible capacities (1208 mA h g⁻¹ for LIBs and 597 mA h g⁻¹ for SIBs at 0.2 A g⁻¹), excellent rate capabilities (829 mA h g⁻¹ for LIBs and 316 mA h g⁻¹ for SIBs at 5 A g⁻¹), and superior long-term cycling performance with a capacity retention of 94.2% for LIBs and 85.2% for SIBs, which has rarely been achieved in previously reported various anodes. Moreover, its highly efficient Li⁺/Na⁺ storage mechanisms are systematically investigated by reaction kinetics analysis and density functional theory calculations, which further provide important insights into the development of high-performance energy storage materials.