Page 336 - Lindens Handbook of Batteries

14.4 PriMAry BATTerieS

14.2 CHEMISTRY

14.2.1 Lithium

The main requirements for electrode materials used for high-performance (high specific energy and
energy density) batteries are a high electrochemical equivalence (high coulombic output for a given
weight of material) and a high electrode potential. it is apparent from Table 14.2, which lists the
characteristics of metals used as battery anodes, that lithium is an outstanding candidate. its stan-
dard potential and electrochemical equivalence are the highest of the metals; it excels in theoretical
gravimetric energy density; and, with its high potential, it is inferior only to aluminum and mag-
nesium on a volumetric energy basis (watthours per liter). Aluminum, however, has not been used
successfully as an anode except in reserve systems, and magnesium has a low practical operating
voltage. Furthermore, lithium is preferred to the other alkali metals because of its better mechanical
characteristics and lower reactivity. Calcium has been investigated as an anode, in place of lithium,
because of its higher melting point (838°C compared with 180.5°C for lithium). To date, practical
cells using calcium have not been produced.

TABLE 14.2 Characteristics of Anode Materials
electrochemical equivalence
Atomic Standard potential Density, Melting Valence
Material weight, g at 25°C, V g/cm 3 point, °C change Ah/g g/Ah Ah/cm 3
Li 6.94 -3.05 0.534 180 1 3.86 0.259 2.08
Na 23.0 -2.7 0.97 97.8 1 1.16 0.858 1.12
Mg 24.3 -2.4 1.74 650 2 2.20 0.454 3.8
Al 26.9 -1.7 2.7 659 3 2.98 0.335 8.1
Ca 40.1 -2.87 1.54 851 2 1.34 0.748 2.06
Fe 55.8 -0.44 7.85 1528 2 0.96 1.04 7.5
Zn 65.4 -0.76 7.1 419 2 0.82 1.22 5.8
Cd 112 -0.40 8.65 321 2 0.48 2.10 4.1
Pb 207 -0.13 11.3 327 2 0.26 3.87 2.9

Lithium is one of the alkali metals, and it is the lightest of all the metallic elements, with a
density about half that of water. When first made or freshly cut, lithium has the luster and color of
bright silver, but it tarnishes rapidly in moist air. it is soft and malleable, can be readily extruded
into thin foils, and is a good conductor of electricity. Table 14.3 lists some of the physical properties
of lithium. 3,4
Lithium reacts vigorously with water, releasing hydrogen and forming lithium hydroxide

2Li + 2HO → 2 2LiOH H 2
+
This reaction is not as vigorous as that of sodium and water, probably due to the fairly low solubility
and the adherence of LiOH to the metal surface under some conditions, however, the heat generated

TABLE 14.3 Physical Properties of Lithium
Melting point 180.5°C
Boiling point 1347°C
3
Density 0.534 g/cm (25°C)
Specific heat 0.852 cal/g (25°C)
6
Specific resistance 9.35 × 10 Ω·cm (20°C)
Hardness 0.6 (Mohs scale)