## 3 Results and Discussion
### Comparison of the Results Obtained from Nanostructured Electrodes Cycled at Different Temperatures  
Figure 11 shows a comparison of the battery response at different temperatures; in all cases, the 500 th cycle was reported. The battery maintained a voltage of below 3 V in all cases, and had no peaks indicating gas production at the electrode surface. Figure 11: Comparison between charge and discharge curves (500 th cycle) at different temperatures. Figure 10: SEM images at different magnifications of Pb and PbO\({}_{2}\) NW electrode after 100 cycles at 10 C at the end of the 1000 th discharge at 40 \(\pm\) 2 \({}^{\circ}\)C: **(a,b)** Pb electrode and **(c,d)** PbO\({}_{2}\) electrode. In the discharge curves, a gradual increase in the plateau of the curves can be seen as the temperature increases. This increase denotes a higher usable energy of the battery, and thus higher efficiency [35]. In particular, for the discharge curve relative to the temperature of 40 \(\pm\) 2 \({}^{\circ}\)C, the cut-off is no longer achieved. This means that the efficiency of this battery has reached 90% and thus all the battery capacity can be converted into usable energy. The discharge curves remained constant over the whole cycling duration at the three temperatures, but different efficiency levels were reached. In particular, battery efficiency increases with temperature, and the maximum efficiency achieved at \(-\)20 \(\pm\) 2 \({}^{\circ}\)C was about 50%. This is a very satisfactory result when compared to the maximum efficiency value of conventional lead-acid batteries, which is 30% under optimum operating conditions. The summarized cyclization results at various temperatures are shown in Table 1. The maximum efficiency increases with temperature; in fact, an efficiency value of 90% was reached at a temperature of 40 \(\pm\) 2 \({}^{\circ}\)C.  
Figure 12 shows, for a better comparison, the SEM images of the Pb (Figure 12a-c) and PbO\({}_{2}\) (Figure 12d-f) nanostructured electrodes after testing at different temperatures. In Figure 12a-c, the Pb electrode is shown and the formation of lead sulfate crystals of different sizes is clearly visible on the electrode surface. In particular, there was a decrease in the average grain size with decreasing temperature. However, the post-cycling electrode surface at different temperatures remained highly porous, which allows the electrolyte to penetrate the active mass and the electrodes to be used for further charge/discharge cycles at high C rates. The post-cycled PbO\({}_{2}\) electrodes, shown in Figure 12d-f, have a widely varying morphology as the operating condition changes. In particular, in Figure 12e, showing a top view of the nanostructured PbO\({}_{2}\) electrode at \(-\)20 \({}^{\circ}\)C, the presence of sulfate agglomerates (of similar shape) can be observed, with sizes of approximately 10-12 \(\upmu\)m distributed over the entire surface, but in particular, a highly porous surface under the agglomerates can be distinguished. The particle size and porosity of lead sulfate is strongly dependent on the discharge conditions, but also temperature, current density, solution concentration and depth of discharge can all affect the lead sulfate crystal structure, leading to a different life cycle. The result of this morphology confirms the trend of the charge and discharge curves shown above and confirms the possibility of diffusion of the electrolyte within the active mass, thus achieving better performance and longer life times despite the critical conditions to which the batteries have been subjected. In all analyzed cases, the presence of small sulfate crystals distributed over the entire electrode surface can be observed. From the micrographs of the nanostructured lead and lead oxide electrodes, it can be seen that the formation of lead sulfate on the electrode surface never occurs as a compact layer, but rather as a mixture of granules that ensure a good porosity for the electrode, which allows battery operation above 1000 charge/discharge cycles.