## 3 Results and Discussion
Figure 3b shows a morphology almost close to the initial one, where the nanowires are still evident, although they have a more pronounced roughness. In addition, lead sulfate microcrystals are also visible on the electrode surface. Based on these results, it can be concluded that nanostructures formed by template electrodeposition change their morphology during the cyclization, generating in situ a porosity that cannot be obtained by other methods. In addition, the increase in volume during discharge does not interrupt the electrolytic continuity between the active electrode material and the current collector, providing a high degree of utilization of the active material. This is perhaps the biggest difference from commercial plates, where the volume increase associated with the conversion reaction interrupts electrolytic continuity between the current grid and the far regions, lowering the degree of utilization of the active material by up to 50%, with associated performance consequences. To limit these problems, commercial plates are cycled at low speeds. Figure 3: SEM images of PbO\({}_{2}\) NW electrode: (**a**) top view before the conditioning phase, (**b**) top view after the conditioning phase, (**c**) cross-sectional view before the conditioning phase and (**d**) cross-sectional view after the conditioning phase. On the Pb NW electrode, after the post-conditioning step, in particular at the end of the 100 th discharge, a quantitative XRD analysis was performed to determine the amount of lead and lead sulfate present in the electrode. Figure 4 shows the result of this analysis. As expected, for an almost fully discharged electrode, PbSO4 is almost 98.9%, while Pb is 1.1%. After the conditioning step, the nanostructured electrodes were tested at different temperatures. Operating temperature is a very important factor for lead-acid batteries and can strongly influence their performance. For example, it has been observed that at high temperatures, internal resistances decrease and reaction kinetics occurring at the electrodes are favored, resulting in an increased capacity and higher energy delivered. However, high temperatures also facilitate self-discharge processes and the consequent capacity loss. If the kinetics is favored at high temperatures, it is disadvantaged at low temperatures. The reactions of the cells slow down, but in spite of this, in the charging phase, it is possible to obtain a final microporous morphology of the electrode (so a very large active surface) that allows to optimize the performance. In this work, nanostructured lead-acid electrodes were tested at 25, \(-\)20 and 40 \({}^{\circ}\)C, the last two being the critical temperatures for a lead-acid battery according to EN 61427-1:2013 [31], at which commercial electrodes are normally tested in order to ensure good performance even at critical temperatures. In this case, the nanostructured electrodes were tested at a C-rate of 10 C, which means charging/discharging the battery in 6 min, with a cut-off of 1.2 V and a discharge rate of 90% of the charge. A number of charge/discharge cycles of 1000 was set for these tests. After the conditioning phase, an initial test was performed at a temperature of \(25\pm 2\) \({}^{\circ}\)C. Figure 5a shows the charging and discharging curves of the battery, while Figure 5b displays the discharge capacity and the efficiency of the nanostructured battery. Figure 5a shows a strong polarization of the electrodes in the first 50 cycles, which decreases with cyclization. The charge curves do not show peaks, meaning that there is a very limited gas development on the electrodes' surface despite the high cyclization rate. The discharge curves show an increase of the plateau with cyclization, which means an increase of usable energy of the battery. We can observe how the curves initially start at a voltage slightly below 3 V and drop to lower voltage values as the number of cycles increases.