The Periodic System of Elements as the Limiting Factor for Galvanic Cell Design

In this chapter, we discuss a fundamental issue for batteries, which is the given limitation in energy density. Galvanic cells, the electrochemical workhorses, which convert chemical energy into electrical energy via spontaneous redox (reduction-oxidation) reactions, depend strongly on the materials forming their electrodes and electrolytes. The periodic system of elements offers a comprehensive catalogue of materials from which scientists and engineers can draw. However, the periodic system also presents limits and challenges that must be considered in the development of high-performance, safe, and durable batteries. No additional element than helium can be invented between hydrogen and lithium. We show that these limitations are based on inherent properties of the periodic system of elements. Among those are electronegativity and electropositivity - properties represented by elements such as lithium (one of the most electropositive ones) and fluorine (the most electronegative one). No compounds can surpass the specific properties of these elements regarding electron structure and thus electronegativity and electropositivity. In other words, if we consider battery cells, they cannot exceed specific voltages since their storage principle is based on chemical potential (redox reactions) rather than an electric field, as is the case with capacitors. Another issue is to make lightweight elements, respectively, ions, such as H+, Li+, and Na+ ions, ready for highly reversible rechargeable battery cells. This requires many more heavy elements, resulting in the fact that, for example, at the end, only about 3 wt.% metallic lithium is present in Li-ion cells. These critical and non-bridgeable facts, probably not in people’s minds due to the visibility of electromobility, deserve thorough discussion in the opening chapter of this book about precise energy.