**5. Working principle and design of ideal solid polymer batteries**

An ideal polymer battery exhibiting a polymer electrolyte membrane, a positive electrode and a negative electrode. The positive electrode is flexible with elastic materials and the negative electrode consists of metal foil. During the recharging process, the direction of flow of electrons takes place in the opposite (anode-to-cathode) direction. Designing new solid-state batteries that have better performance over the life cycle also depends on the outstanding operation of electrode–electrolyte interfaces, as shown in **Figure 12**.

Most polymeric materials are insulators that do not conduct electricity in the medium through ions or electrons. Some of the polymers are "immobile solvents" at which the salt and the polymer are completely mixed and act as a polymer electrolyte [27–31]. Compared to solid electrolytes, polymer electrolytes have both cations and anions in the mobile state. Due to this, polymer batteries designed to be rechargeable face several challenges. Fabrication of polymer batteries is an important method to pass ions from the anode to the cathode. Here, sodium metal was considered an anode and carbon mixed with iodine was taken as a cathode material.

**Figure 12.** *Schematic diagram of a solid polymer battery.*

**Figure 13.** *Fabrication and operation of a solid-state battery.*

For some PEO N:LiCF3SO3, mobilization takes place at the anode due to anions, and it reacts with Li + cations, which form a thin layer of lithium salt and act as a conducting medium.

$$\text{Li}^\* + \text{X}^- \text{LiX}$$

The results show that the battery resistance is increased, and Li + ions decrease the capacity. Polarization takes place in an electrolyte due to the mobility of ions in the battery system with respect to negative ions.

#### **5.1 Discharge characteristics of a solid-state battery**

Solid-state batteries provide well-contained energy conversion devices, which greatly contribute to the needs of humankind. Zero-emission vehicles of the future will be battery powered only. Many nonpolluting energy conversion devices, such as photovoltaic systems, require the concomitant use of rechargeable batteries for energy storage. Batteries may be considered storehouses for electrical energy [1–4, 6–10]. The size of a battery ranges from a tiny coin to that of a large house. Tiny coin and button-sized cells are used for electronic applications requiring only small capacity. Liter-container sized batteries are commonly used in motor vehicles for starting, lighting, and ignition purposes. The basis for battery technology is that the chemical energy derived from the chemical reactions in the battery is transformed into electrical energy. **Figure 13** shows the fabrication and operation of a solid-state battery.
