Hierarchically Well‐Developed Porous Graphene Nanofibers Comprising N‐Doped Graphitic C‐Coated Cobalt Oxide Hollow Nanospheres As Anodes for High‐Rate Li‐Ion Batteries

Abstract

Hierarchically well‐developed porous graphene nanofibers comprising N‐doped graphitic C (NGC)‐coated cobalt oxide hollow nanospheres are introduced as anodes for high‐rate Li‐ion batteries. For this, three strategies, comprising the Kirkendall effect, metal–organic frameworks, and compositing with highly conductive C, are applied to the 1D architecture. In particular, NGC layers are coated on cobalt oxide hollow nanospheres as a primary transport path of electrons followed by graphene‐nanonetwork‐constituting nanofibers as a continuous and secondary electron transport path. Superior cycling performance is achieved, as the unique nanostructure delivers a discharge capacity of 823 mAh g−1 after 500 cycles at 3.0 A g−1 with a low decay rate of 0.092% per cycle. The rate capability is also noteworthy as the structure exhibits high discharge capacities of 1035, 929, 847, 787, 747, 703, 672, 650, 625, 610, 570, 537, 475, 422, 294, and 222 mAh g−1 at current densities of 0.5, 1.5, 3, 5, 7, 10, 12, 15, 18, 20, 25, 30, 40, 50, 80, and 100 A g−1, respectively. In view of the highly efficient Li+ ion/electron diffusion and high structural stability, the present nanostructuring strategy has a huge potential in opening new frontiers for high‐rate and long‐lived stable energy storage systems.

Porous nanofibers comprising hollow Co 3 O 4 / Fe 3 O 4 nanospheres and nitrogen‐doped carbon derived by Fe@ ZIF ‐67 as anode materials for lithium‐ion batteries

“…In the N 1s XPS spectrum (Figure 4E), the pyrrolic-N at 400 eV, graphitic-N at 400.9 eV, and oxidized-N species at 401.9 eV are detected. 26,39 These peaks confirm N-doping into carbon. Raman spectroscopy is analyzed as shown in Figure 4F to confirm the crystallinity of the carbon material of A300NF.…”

“…2-mIM, as an organic linker of Fe@ZIF-67, acts as an Ndoping source under N 2 atmosphere. 25,26 Further, during carbothermal reduction, metallic Co and CoFe crystals play the role of catalysts for the graphitization of carbon formed by PAN. 25,26 Thus, carbonization of both the organic linker of Fe@ZIF-67 and PAN into graphitic carbon (GC) doped with N leads to metallic Co and CoFe nanospheres coated with N-doped GC (N-GC) in the structure.…”

“…25,26 Further, during carbothermal reduction, metallic Co and CoFe crystals play the role of catalysts for the graphitization of carbon formed by PAN. 25,26 Thus, carbonization of both the organic linker of Fe@ZIF-67 and PAN into graphitic carbon (GC) doped with N leads to metallic Co and CoFe nanospheres coated with N-doped GC (N-GC) in the structure. After the second heat treatment in an air atmosphere, the filled Co and CoFe metals dispersed within the N-GC matrix are converted into hollow structured Co 3 O 4 and Fe 3 O 4 nanospheres by the well-known Kirkendall diffusion effect (Scheme 1-③).…”

“…Thus, smaller I D /I G ratio indicates higher is degree of ordering in carbon materials. 26,30 The Co/CoFe/N-GC composite nanofibers exhibit I D /I G ratio of $0.96; it demonstrates that the carbon matrix in the composite is ordered, that is, it is graphitic carbon. From the HR-TEM image (Figure 2E), metallic particles are surrounded by the GC layer, and they show the core shell structure.…”

Nanostructured Graphene Oxide-Based Hybrids as Anodes for Lithium-Ion Batteries

“…The use nitrogen-doped rGO (N-rGO) is a promising strategy for the development of anode materials for LIBs with high electrochemical performance [491,492]. Li et al [492] Hierarchically well-developed porous graphene nanofibers comprising N-doped graphitic carbon (NGC)-coated cobalt oxide hollow nanospheres were tested as anodes for high-rate Li-ion batteries [493]. This nanostructured composite delivers a discharge capacity of 823 mAh g −1 after 500 cycles at 3.0 A g −1 current density with a low decay rate of 0.092% per cycle.…”