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The introduction of a functional interlayer between the cathode and anode in lithium–sulfur battery (LSB) technology results in significant improvements in electrochemical performance. Here, we developed hierarchically structured porous, conductive, and multifunctional N-doped carbon (N-C) nanofibers comprising homogeneously dispersed vanadium nitride quantum dots and hollow N-C nanocages as functional interlayers for advanced LSBs. The freestanding interlayer contains well-developed long-range channels and numerous interconnected hollow N-C nanocages derived from the metal–organic framework. Furthermore, the presence of a N-C framework and vanadium nitride quantum dots measuring several nanometers improves the redox reaction kinetics and provides numerous chemisorption sites for the effective trapping and reuse of lithium polysulfide. As a result, the assembled Li–S cell employing the unique nanostructured freestanding interlayer exhibits superior rate capability and stable cycling performance (decay rate of 0.02% per cycle at 0.5C) considering the high sulfur content (80 wt%) and loading (ca. 4 mg cm−2) in the sulfur electrodes. Even with an ultra-high sulfur loading of 11.0 mg cm−2, the Li–S cell delivered a stable areal capacity of 5.0 mA h cm−2 after 100 charge–discharge cycles at 0.05C. Thus, the uniquely nanostructured interlayer shows high potential for the development of advanced LSBs utilizing pure sulfur electrodes with realistic battery parameters.

Porous nanofibers composed of few-layered MoSe2 nanosheets and highly densified-entangled N-doped carbon nanotubes (N-CNTs) are designed as anodes for Na ion batteries. To maximize the electrical conductivity of the composite nanofibers, amorphous carbon formed by polyacrylonitrile (PAN) decomposition is selectively removed except N-CNTs by intermediate heat treatment. During this step, numerous mesopores are formed between the N-CNTs. Final selenization results in the formation of porous nanofibers composed of few-layered MoSe2 nanosheets and highly densified-entangled-N-CNTs (P-MoSe2/N-CNT NF). The discharge capacity of P-MoSe2/N-CNT NF after 300 cycles is 372 mA h g-1, which is a 100% capacity retention calculated from the 2nd cycle onward. P-MoSe2/N-CNT NF show capacities of 404, 318, 245, 210, 169, 144, 115, and 74 mA h g-1 at current densities of 0.2, 2, 5, 7, 10, 12, 15, and 20 A g-1, respectively. Synergetic effects of the N-CNT matrix, uniformly dispersed mesopores, and few-layered MoSe2 nanosheets result in efficient diffusion of Na+ during uptake/removal and rapid transport of electrons by improving the electrical contact between the MoSe2 nanosheets and electrodes.

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.