Page 77 - Handbook of Battery Materials

2.5 Lithium Primary Batteries 43

2.5
Lithium Primary Batteries
The electrode potential of lithium is −3.01 V vs normal hydrogen electrode (NHE),
which is the lowest value among all the metals. Lithium has the lowest density
−3
−1
(0.54 g cm ) and the lowest electrochemical equivalent (0.259 g Ah ) of all solids.
As a result of these physical properties, nonaqueous electrolyte batteries using
lithium offer the possibility of high voltage and a high energy density. Organic and
inorganic solvents which are stable with lithium are selected as the electrolytes for
lithium batteries.
Primary lithium batteries offer these advantages as well as good low-temperature
characteristics. There are many kinds of primary lithium batteries, with vari-
ous cathode active materials; the main ones are lithium–manganese dioxide,
lithium–carbon monofluoride, and lithium–thionyl chloride batteries [28].
2.5.1
Lithium–Manganese Dioxide Batteries

MnO 2 is used for the same purpose as the cathode active material in lithium–
manganese dioxide (Li–MnO 2 ) batteries; it has been used for a long time
in zinc–carbon and alkaline–manganese dioxide batteries, which are aqueous-
electrolyte systems. In 1975, the Sanyo Electric Co. identified a novel reaction be-
tween lithium and MnO 2 and succeeded in exploiting this as the Li–MnO 2 battery.
Sanyo has also granted the manufacturing technology for Li–MnO 2 batteries to
major battery manufacturers around the world, and more than 15 companies are
now producing it worldwide.
The following reaction mechanism is suggested to occur in Li–MnO 2 :
+
Anode reaction: Li → Li + e − (2.10)
−
Cathode reaction: MnO 2 + Li + e → MnO (Li ) (2.11)
+
−
+
2
+
Overall battery reaction: MnO 2 + Li → MnO (Li ) (2.12)
−
2
− +
where MnO (Li ) signifies that the lithium ion is introduced into the MnO 2
2
crystal lattice.
Figure 2.26 shows a schematic representation of the solid phase during the
discharge of the MnO 2 crystal lattice, where tetravalent manganese is reduced to
trivalent manganese.
In Li–MnO 2 batteries, lithium perchlorate (LiClO 4 ) or lithium trifluoromethane-
sulfonate (LiCF 3 SO 3 ) is widely employed as an electrolytic solute, and mainly
propylene carbonate (PC) and 1,2-dimethoxyethane (DME) are employed as
a mixed solvent. The PC–DME–LiCLO 4 electrolyte shows high conductivity
−1
(>10 −2 −1 cm ) and low viscosity (<3cP).
The requirements for the MnO 2 active material in Li–MnO 2 batteries are as
follows:
1) It must be almost anhydrous.
2) It must have an optimized crystal structure suitable for the diffusion of Li +
ions into the MnO 2 crystal lattice.