## 3 Results
### Strategies to Improve the Electrochemical Performance of the Investigated Samples
#### 3.4.2 Incorporating the Oxide in a Carbonaceous Matrix  
Incorporating the active oxide particles in a carbonaceous matrix is a commonly adopted strategy to improve the electrochemical performance of anode materials prepared using different methods [43; 44]. The carbon matrix favours the electrical transport and withstands the large volume changes, preventing the pulverization of the oxide particles.  
Here, a composite carbon/HESO sample, coded as C5 MF-b, is produced by ES followed by stabilization and carbonization. The sample, with nominal composition C/(Cr\({}_{0.2}\)Mn\({}_{0.2}\)Fe\({}_{0.2}\)Co\({}_{0.2}\)Zn\({}_{0.2}\))\({}_{3}\)O\({}_{4}\), exhibits a fibrous structure, similar to pure HESO (Figures S12 and S13). TEM/EDX analysis (Figure S14) reveals that the sample contains both C-poorer (Figure S13a,c) and C-richer NFs (Figure S14b,d). In the former, the oxide grains are generally larger (Figure S13a), whereas in the latter, they are finer (Figure S13b-d), in agreement with the well assessed ability of carbon to reduce the size of oxide grains and prevent their agglomeration [42; 43; 44]. In the micro-Raman spectrum of sample C5 MF-b (Figure S15), the Raman fingerprints of both amorphous carbon [35; 36] and (Cr,Mn,Fe,Co,Zn) HESO particles are detected.  
Figure 7 compares the electrochemical properties of anodes 5 MF-b and C5 MF-b. Looking at their CV profiles (Figure 7a,b), it can be seen that the peak intensity and CV curve area of C5 MF-b are higher than that of 5 MF-b, implying that C/HESO NFs have better electrochemical kinetics [70]. Moreover, the second and third charge/discharge curves of anode C5 MF-b are overlapped very well (Figure 7d), unlike those of 5 MF-b (Figure 7c). This indicates that the composite NFs have better stability and reversibility for Li\({}^{+}\) insertion and extraction reactions than the pure HESO NFs [43]. Due to the specific capacity of carbon (372 mAh g\({}^{-1}\)) [42; 43; 44], the C/HESO NFs exhibit lower initial lithiation/delithiation capacities compared to HESO NFs (1159/777 against 1297/950 mAh g\({}^{-1}\)). Figure 7e,f compares the results of the rate capability test carried out on anodes 5 MF-b and C5 MF-b. The measured delithiation capacities of C/HESO NFs are 834, 835, 784, 727, 610, 526, 471 and 345 mAh g\({}^{-1}\) at 20, 50, 100, 200, 500, 1000 and 2000 mA g\({}^{-1}\), respectively. These values are higher than those measured in pure HESO NFs, especially at high current density, as expected [42; 43; 44]. In the long-term cyclability test (Figure 7g), the capacity decreases during the first 100 cycles and then increases. These capacity changes can be explained by the activation process and structural reconstruction associated with the  
Active material [31]. After 400 cycles at a rate of 500 mA g\({}^{-1}\), C/HESO NFs deliver a capacity of around 545 mAh g\({}^{-1}\), which is much higher than that of 5 MF-b (265 mAh g\({}^{-1}\)). The results of EIS measurements (Figure 7h) evidence that the charge transfer resistance of C5 MF-b is significantly lower than that of 5 MF-b, confirming that the improvement in the electrochemical performance can be ascribed to the enhanced eletronic conductivity and mechanical stability promoted by carbon rather than to changes in the ionic transport.