Design Nitrogen (N) and Sulfur (S) Co-Doped 3D Graphene Network Architectures for High-Performance Sodium Storage

To develop high-performance sodium-ion batteries (NIBs), electrodes should possess well-defined pathways for efficient electronic/ionic transport. In this work, high-performance NIBs are demonstrated by designing a 3D interconnected porous structure that consists of N, S co-doped 3D porous graphene frameworks (3DPGFs-NS). The most typical electrode materials (i.e., Na₃ V₂ (PO₄ )₃ (NVP), MoS₂ , and TiO₂ ) are anchored onto the 3DPGFs-NS matrix (denoted as NVP@C@3DPGFs-NS; MoS₂ @C@3DPGFs-NS and TiO₂ @C@3DPGFs-NS) to demonstrate its general process to boost the energy density of NIBs. The N, S co-doped porous graphene structure with a large surface area offers fast ionic transport within the electrode and facilitates efficient electron transport, and thus endows the 3DPGFs-NS-based composite electrodes with excellent sodium storage performance. The resulting NVP@C@3DPGFs-NS displays excellent electrochemical performance as both cathode and anode for NIBs. The MoS₂ @C@3DPGFs-NS and TiO₂ @C@3DPGFs-NS deliver capacities of 317 mAhg^-1 at 5 Ag^-1 after 1000 cycles and 185 mAhg^-1 at 1 Ag^-1 after 2000 cycles, respectively. The excellent long cycle life is attributed to the 3D porous structure that could greatly release mechanical stress from repeated Na⁺ extraction/insertion. The novel structure 3D PGFs-NS provides a general approach to modify electrodes of NIBs and holds great potential applications in other energy storage fields.