Interlayer and Doping Engineering in Partially Graphitic Hollow Carbon Nanospheres for Fast Sodium and Potassium Storage

Constructing anodes with fast ions/electrons transfer paths is an effective strategy to achieve high-performance sodium ion batteries (SIBs)/potassium ion batteries (PIBs). Amorphous carbon is a promising candidate anode for SIBs/PIBs owing to its disordered carbon layers, abundant defects/pores, and low-cost resources. However, the larger radius of Na+/K+ leading to depressed kinetics and poor cycling performance, impeding their further applications. Herein, we propose an efficient strategy to construct of nitrogen, sulfur co-doped hollow carbon nanospheres (NS-HCS) involving an in situ growth of polydopamine on nano-Ni(OH)2 template with subsequent sulfur doping process. During the formation process, the produced Ni nanospheres play as the hard template and catalyst for the formation of hollow carbon nanosphere with partially graphite microcrystalline structure, while the sulfur doping process can enlarge the interlayer space and create more defects on the surface of carbon nanospheres, thus synchronous improve the Na+/K+ insertion and adsorption ability in NS-HCS. With the synergistic control of the enlarged interlayer spacing, high content of pyridinic N/pyrrolic N and graphitization, a hybrid storage mechanism facilitates the transport kinetics and endows the NS-HCS electrode with high capacities and good cycling stability in SIBs and PIB. Benefit from the multiple effects, NS-HCS exhibits the improved capacity of 274.8 mAh/g at 0.1 A/g and excellent cycling stability of 149.5 mAh/g after 5000 cycles at 2.5A/g in SIBs, as well as good potassium ion storage behavior with a high capacity retention of 76.5% after 700 cycles at 1.0 A/g, demonstrating the potential applications of NS-HCS for high-performance SIBs and PIBs