Nitrogen and sulfur dual-doped carbon films as flexible free-standing anodes for Li-ion and Na-ion batteries

Heteroatom doping is considered to be one of the most effective approaches to improve the electrochemical activity of carbon-based electrode materials for both Li-ion batteries (LIBs) and Na-ion batteries (SIBs) due to introduction of unbalanced electron atmosphere and enlarged interlayers of carbon materials. Here, we present nitrogen and sulfur dual-doped flexible carbon (NSC) film as a promising free-standing anode for stable high-power and high-energy LIBs or SIBs. The NSC film delivers high reversible capacities of 965.7 mAh g−1 in LIBs and 520.1 mAh g−1 in SIBs at a current density of 100 mA g−1. Particularly, the film electrodes exhibit excellent high-rate capability and remarkable long-term cyclability. For instance, as a LIBs anode, the NSC film remained a high capacity of 357.2 mAh g−1 at 2.0 A g−1 (∼10 min to full charge) after 2000 cycles; even in SIBs, a capacity of 155 mAh g−1 can also be reached at 1.0 A g−1. It is believed that the interconnected conducting structure of carbon backbones, heteroatomic defects and increased carbon interlayers distance by stable SC and NC bonds are beneficial to ultrafast ion diffusion and electron transport, making the NSC film become a high performance free-standing anode for LIBs or SIBs application.