Flame-assisted ultrafast synthesis of functionalized carbon nanosheets for high-performance sodium storage

The unique structural features of hard carbon (HC) make it a promising anode candidate for sodium-ion batteries (SIB). However, traditional methods of preparing HC require special equipment, long reaction times, and large energy consumption, resulting in low throughputs and efficiency. In our contribution, a novel synthesis method is proposed, involving the formation of HC nanosheets (NS-CNs) within minutes by creating an anoxic environment through flame combustion and further introducing sulfur and nitrogen sources to achieve heteroatom doping. The effect of heterogeneous element doping on the microstructure of HC is quantitatively analyzed by high-resolution transmission electron microscopy and image processing technology. Combined with density functional theory calculation, it is verified that the functionalized HC exhibits stronger Na⁺ adsorption ability, electron gain ability, and Na⁺ migration ability. As a result, NS-CNs as SIB anodes provide an ultrahigh reversible capacity of 542.7 mAh g⁻¹ at 0.1 A g⁻¹, and excellent rate performance with a reversible capacity of 236.4 mAh g⁻¹ at 2 A g⁻¹ after 1200 cycles. Furthermore, full cell assembled with NS-CNs as the can present 230 mAh g⁻¹ at 0.5 A g⁻¹ after 150 cycles. Finally, in/ex situ techniques confirm that the excellent sodium storage properties of NS-CNs are due to the construction of abundant active sites based on the novel synthesis method for realizing the reversible adsorption of Na⁺. This work provides a novel strategy to develop novel carbons and gives deep insights for the further investigation of facile preparation methods to develop high-performance carbon anodes for alkali-ion batteries.