Page 337 - Lindens Handbook of Batteries

LiTHiUM PriMAry BATTerieS 14.5

by this reaction may ignite the hydrogen that is formed and the lithium will then also burn. Because
of this reactivity, however, lithium must be handled in a dry atmosphere and, in a battery, be used with
nonaqueous electrolytes. (The lithium/water and lithium/air batteries are described in Chap. 33.)

14.2.2 Cathode Materials
A number of inorganic and organic materials have been examined for use as the cathode in primary
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lithium batteries. The critical requirements for this material to achieve high performance are high
battery voltage, high energy density, and compatibility with the electrolyte (that is, being essentially
nonreactive or insoluble in the electrolyte). Preferably the cathode material should be conductive,
although there are few such materials available and solid cathode materials are usually mixed with
a conducting material, such as carbon, and applied to a conductive grid to provide the needed con-
ductivity. if the cathode reaction products are a metal and a soluble salt (of the anode metal), this
feature can improve cathode conductivity as the discharge proceeds. Other desirable properties of the
cathode material are low cost, availability (noncritical material), and favorable physical properties,
such as nontoxicity and nonflammability. Table 14.4 lists some of the cathode materials that have
been studied for primary lithium batteries and gives their cell reaction mechanisms and the theoreti-
cal cell voltages and capacities.

14.2.3 Electrolytes
The reactivity of lithium in aqueous solutions requires the use of nonaqueous electrolytes for lithium
anode batteries. Polar organic liquids are the most common electrolyte solvents for the active
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primary cells, except for the thionyl chloride (SOCl ) and sulfuryl chloride (SO Cl ) cells, where
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these inorganic compounds serve as both the solvent and the active cathode material. The important
properties of the electrolyte are:
1. it must be aprotic, that is, have no reactive protons or hydrogen atoms, although hydrogen atoms
may be in the molecule.
2. it must have low reactivity with lithium (or form a protective coating on the lithium surface to
prevent further reaction) and the cathode.
3. it must be capable of forming an electrolyte of good ionic conductivity.
4. it should be liquid over a broad temperature range.
5. it should have favorable physical characteristics, such as low vapor pressure, stability, nontoxic-
ity, and nonflammability.
A listing of the organic solvents commonly used in lithium batteries is given in Table 14.5. These
solvents are typically employed in binary or ternary combination. These organic electrolytes, as well
as thionyl chloride (mp -105°C, bp 78.8°C) and sulfuryl chloride (mp -54°C, bp 69.1°C), are liquid
over a wide temperature range with low freezing points. This characteristic provides the potential for
operation over a wide temperature range, particularly low temperatures.
The Jet Propulsion Laboratory (Pasadena, CA) has evaluated several types of lithium primary
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batteries to determine their ability to operate planetary probes at temperatures of -80°C and below.
individual cells were evaluated by discharge tests and electrochemical impedance Spectroscopy. Of
the five types considered (Li/SOCl , Li/SO , Li/MnO , Li-BCX, and Li-CFx), lithium-thionyl chlo-
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ride and lithium-sulfur dioxide were found to provide the best performance at -80°C. Lowering the
electrolyte salt to ca. 0.5 molar was found to improve performance with these systems at very low
temperatures. in the case of D-size Li/SOCl batteries, lowering the LiAlCl concentration from 1.5
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to 0.5 molar led to a 60% increase in capacity on a baseline load of 118 ohms with periodic 1-min
pulses at 5.1 ohms at -85°C.
Lithium salts, such as LiClO , LiBr, LiCF SO , Lii, and LiAlCl , are the electrolyte solutes most
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commonly used to provide ionic conductivity. The solute must be able to form a stable electrolyte