Probing the active sites of 2D nanosheets with Fe-N-C carbon shell encapsulated FexC/Fe species for boosting sodium-ion storage performances
Huicong Xia, Pengfei Yuan, Lingxing Zan, Gan Qu, Yunchuan Tu, Kaixin Zhu, Yifan Wei, Zeyu Wei, Fangying Zheng, Mo Zhang, Yongfeng Hu, Dehui Deng, Jianan Zhang
Abstract
Developing stable but high active metal-nitrogen-carbon (M-N-C)-based hard carbon anode is a promising way to be the alternatives to graphene and blank hard carbon for sodium-ion batteries (SIBs), requiring the precise tailoring of the electronic structure for optimizing the Na+ intercalation behavior, yet is greatly challenging. Herein, Fe-N-C graphitic layer-encapsulating Fe3C species within hard carbon nanosheets (Fe-N-C/Fe3C@HCNs) are rationally engineered by pyrolysis of self-assembled polymer. Impressively, the Fe-N-C/Fe3C@HCNs exhibit outstanding rate capacity (242 mAh·g−1 at 2,000 mA·g−1), which is 2.1 and 4.2 times higher than that of Fe-N-C and N-doped carbon (N-C), respectively, and prolonged cycling stability (176 mAh·g−1 at 2,000 mA·g−1 after 2,000 cycles). Theoretical calculations unveil that the Fe3C species enhance the electronic transfer from Na to Fe-N-C, resulting in the charge redistribution between the interfaces of Fe3C and Fe-N-C. Thus, the optimized adsorption behavior towards Na+ reduces the thermodynamic energy barriers. The synergistic effect of Fe3C and Fe-N-C species maintains the structural integrity of electrode materials during the sodiation/desodiation process. The in-depth insight into the advanced Na+ storage mechanisms of Fe3C@Fe-N-C offers precise guidance for the rational establishment of confinement heterostructures in SIBs.