Ion-catalyzed synthesis of N/O co-doped carbon nanorods with hierarchical pores for high-rate Na-ion storage.

Appropriate heteroatom doping and pore structure optimization are cost-effective technologies to improve the electronic conductivity and ion diffusion kinetics of hard carbons (HCs). Here, we report an ion-catalyzed synthesis of N/O co-doped carbon nanorods (NOCNRs) with abundant hierarchical pores, achieving high-capacity and high-rate Na-ion storage (336 mA h g-1 at 0.1 A g-1 and 196 mA h g-1 at 20.0 A g-1).

Enhancing High-Capacity and High-Rate Sodium-Ion Storage through Synergistic N,S Dual Doping of Hard Carbon.

Hard carbon, as the most promising commercial anode materials of sodium-ion batteries (SIBs), has suffered from the coupling limitations on initial Coulombic efficiency (ICE), capacity, and rate capability. Herein, to break such coupling limitations, sulfur-rich nitrogen-doped carbon nanomaterials (S-NC) were synthesized by a synergistic modification strategy, including structure/morphology regulation and dual heteroatom doping. The small specific surface area of S-NC is beneficial for inhibiting excessive growth of solid electrolyte interphase (SEI) film and irreversible interfacial reaction. The covalent S can serve as active electrochemical sites by Faradaic reactions and provide extra capacity. Benefit by N, S co-doping, S-NC shows large interlayer spacing, high defects, good electronic conductivity, strong ion adsorption performance, and fast Na+ ion transport, which combined with a more significant pore volume result in speedier reaction kinetics. Hence, S-NC possesses a high reversible specific capacity of 464.7 mAh g-1 at 0.1 A g-1 with a high ICE of 50.7%, excellent rate capability (209.8 mAh g-1 at 10.0 A g-1 ), and superb long-cycle capability delivering a capacity of 229.0 mAh g-1 (85% retention) after 1800 cycles at 5.0 A g-1 .

Regulating Oxygen Configuration in Hierarchically Porous Carbon Nanosheets for High-Rate and Durable Na+ Storage.

Surface oxygen functionalities (particularly C-O configuration) in carbon materials have negative influence on their electrical conductivity and Na+ storage performance. Herein, we propose a concept from surface chemistry to regulate the oxygen configuration in hierarchically porous carbon nanosheets (HPCNS). It is demonstrated that the C-O/C=O ratio in HPCNS reduces from 1.49 to 0.43 and its graphitization degree increases by increasing the carbonization temperature under a reduction atmosphere. Remarkably, such high graphitization degree and low C-O content of the HPCNS-800 are favorable for promoting its electron/ion transfer kinetics, thus endowing it with high-rate (323.6 mAh g-1 at 0.05 A g-1 and 138.5 mAh g-1 at 20.0 A g-1 ) and durable (96 % capacity retention over 5700 cycles at 10.0 A g-1 ) Na+ storage performance. This work permits the optimization of heteroatom configurations in carbon for superior Na+ storage.