# Electrospinning-Based Carbon Nanofibers for Energy and Sensor Applications
## 4 Application of Carbon Nanofibers
### Energy Storage Applications
#### 4.1.3 Lithium-Sulfur Battery  
Lithium-sulfur batteries operate using electron transfers from the electrode to the electrolyte, as well as interactions between lithium ions and sulfur molecules. During charging, the lithium-ion can be oxidized into sulfur and the opposite happens in the discharge process. Improving the electrical conductivity or surface resistance of electrodes is one of the most popular ways to improve the working performance of a lithium-sulfur device [100].  
[PERSON] et al. introduced sulfur-host porous CNFs containing MoS\({}_{2}\) that act as cathode material for a lithium-sulfur battery (Figure 14a) [101]. The precursor solution is PAN  
Figure 13: (a) Lithium-ion battery using CNF-decorated MnO\({}_{2}\) nanosheets for anode material [96]. (b) Anode constructed from CNFs containing MXene used for lithium-ion battery [97]. (c) Hollow CNF-embedded Si nanoparticles on inner wall [98]. (d) CNFs/urchin-shaped V\({}_{2}\)O\({}_{5}\) particle for lithium-ion battery electrode [99].  
mixed with ammonium tetrathiomolybdate ((NH\({}_{4}\))\({}_{2}\)MoS) and hydrophobic-fumed silica powder. After calcination, the collected CNFs contain both MoS\({}_{2}\) and silica oxide (SiO\({}_{2}\)). The material is then subjected to a chemical etching process to remove SiO\({}_{2}\) and create a porous fiber structure. The fiber precursor containing (NH\({}_{4}\))\({}_{2}\)MoS was found to be more stable compared to the precursor without (NH\({}_{4}\))\({}_{2}\)MoS. It can retain the fiber structure after annealing at high temperatures. The results showed that CNFs with MoS\({}_{2}\) had a greater pore volume and capacity.  
ZIF is a MOF material that contains a large number of nitrogen function groups, so the decoration of ZIF material can be a potential method of increasing the capacity of energy storage devices [102]. [PERSON] et al. investigated a nitrogen-doped CNFs framework with ZIF-8 as the host of the functional groups (Figure 14b) [103]. Though the deposited ZIF could not enhance the surface area or the pore volume, it was able to reduce the surface resistance of the electrode. The smaller resistance allowed for smoother electron flow and an increase in material capacity.  
To increase the working performance of the CNFs with surface modifications, we can increase the pore volume or the surface area of the outside wall. [PERSON] et al. described the effect of the inner wall on the battery capacity with multichannel CNFs (Figure 14c) [104]. The authors prepared two different CNFs using PMMA, MMA, and PAN. Although one sample carried multichannel CNFs, the other was created with one big channel in the middle of the CNFs using a dual nozzle. Though the surface area of the sample fabricated with the dual nozzle is smaller, the pore volume seems to be much larger. The cycle stability has also been proven to be an advantage of the larger-sized channel. Another work based on the multichannel CNFs was conducted by [PERSON] et al. (Figure 14d) [105]. In this study, the pore network was made by the base-treatment method using potassium hydroxide (KOH). This method created a larger pore volume compared to the pores obtained from PMMA decomposition in the study of [PERSON] et al. [104]. In addition, KOH-treated multichannel CNFs appear to have longer cycle stability when embedded with sulfur and are operating as a lithium-sulfur battery.  
Figure 14: (**a**) Porous CNFs embedded with sulfur applied for lithium\(-\)sulfur batteries [101]. (**b**) CNFs contain MOF material for nitrogen function group doping [103]. (**c**) Porous, hollow multichannel CNFs for lithium-sulfur battery [104]. (**d**) Multichannel porous CNFs using KOH-treatment process embedded with sulfur [105].