**3. Battery Technologies**

## *3.1. Lead–Acid Battery*

The lead–acid battery, created in 1859, is the first kind of rechargeable battery ever developed [23]. Lead–acid batteries have a suboptimal energy density when compared to contemporary rechargeable batteries.

Lead–acid cells are composed of lead alloy grids (solid electrodes) that operate as current collectors and mechanically support the positive and negative active elements. The grids are interlaced with a permeable, electrically isolator and arrayed as positive and negative plates. The plate stack is embedded into an adequately contoured polymer housing to embody the cell elements and the electrolyte with the coupled positive and negative plates, terminals, a lid and venting arrangements. The construction of a lead–acid battery is shown in Figure 5.

The operating voltage of the lead–acid cell is reasonably high at approximately 2.05 V. The positive active material (PAM) is considerably permeable lead dioxide (PbO2) and the negative active material (NAM) is delicately isolated lead. The electrolyte utilized in the discharge process is thinned liquefied sulfuric acid (HSO4). HSO4 ions move to the negative electrode during discharge, producing H+ ions and lead sulfate (SO4 <sup>2</sup>−). Lead dioxide reacts with the electrolyte at the positive electrode to yield lead sulfate particles and water (H2O), as shown in Figure 6. Both electrodes are discharged to a feeble conductor, lead sulfate (PbSO4), and the electrolyte is incrementally diluted as the discharge progresses. On charging, the reactions are reversible [24,25].

**Figure 5.** Lead–acid battery construction.

**Figure 6.** Chemistry of lead–acid battery.

The most recent innovations [26,27] have used enhanced lead batteries in a variety of grid-related plans as well as smaller-scale industrial and domestic energy storage applications. In recent years, systems with integrated super-capacitors have been described in addition to conventional lead–acid batteries; they are commonly referred to as carbonenhanced (LC) lead batteries. These could have a negative electrode made of a mix of lead–acid and supercapacitor negatives made of carbon. The positive electrode is exactly like the one in a typical lead–acid battery in every way. The current tendency in operating renewable energy sources, especially solar PV sources, is for periodic discharges rather than a continuous restoration of the battery to a full state of charge (SOC). This partial state-of-charge (PSoC) behavior can be detrimental to lead–acid batteries since it induces permanent corrosion of the negative electrode, and sustainable development strategies are still being investigated [28,29].
