Contrary to popular misconceptions, lithium batteries are not all alike. Lithium battery chemistries differ in several important characteristics. The critical considerations are voltage, discharge current, service life and temperature range. Under the broad category of primary lithium battery types, several chemical systems are commonly used.
In the consumer area, Li/CFX (poly carbon monofluoride) and Li/MN02 (manganese dioxide) are found in cameras, calculators and watches. In the military area, Li/SO2 (sulfur dioxide) batteries are used in high power radios. Li/SOCl2 (thionyl chloride) and LiI2 (lithium iodine) are commonly utilized in industrial and medical applications.
Table 1. Characteristics of the main Lithium Battery Systems used in automotive applications.
Li/CFX cells have an OCV of 2.8 V and moderate energy density. Cylindrical types are manufactured with a spiral cathode for higher rate capability and have crimped plastic seals. Though generally safe, under extreme conditions, the elastomer seal can break, allowing the cell to fail due to loss of the low vapor point electrolyte. This is especially true in areas of high temperature and humidity.
Li/MN02 3.0 V cells are similar to Li/CFX cells in terms of construction and problems with high temperature and humidity. Their energy density and voltage is slightly better than Li/CFX cells, especially at cold temperatures.
Li/SO2 2.8 V cells are used almost exclusively in military/aerospace applications. Their chief attribute is the ability to deliver high current, especially at cold temperatures. The main drawback also stems from this high rate capability. The electrolyte within the cell is kept in a liquid state by maintaining 2 atmospheres of pressure within the cell. The cells are vented to prevent over pressurization. As a result, service life and energy density of Li/SO2 cells are typically less than half that of lithium thionyl chloride cells.
Li/SOCl2 -- Lithium thionyl chloride 3.6 V cells have the highest energy density and voltage of all commercial lithium types, with a service life of up to 15 to 20 years. These cells are ideal for applications requiring very low continuous-current and/or moderate pulse-currents. Extremely long service life and low self-discharge make them ideal for life-saving devices such as automatic external defibrillators that must be ready for use at all times without risk of battery failure.
Bobbin-type vs. Spirally Wound
Bobbin-type lithium Li/SOCl2 cells are particularly well suited for low-current applications due to their high energy density, very low self-discharge rate, and 15 to 20 year storage life. Bobbin-type lithium thionyl chloride cells also offer extended temperature ranges from -55°C to +150°C. High capacity, small size, and an ability to withstand broad fluctuations in pressure, temperature and shock make bobbin-type cells ideal for use in remote monitoring applications.
High current pulse "hybrid" solutions
Spirally wound lithium thionyl chloride batteries deliver the energy density demanded by high current pulse applications. However, this chemistry lacks the required capacity, and has a comparatively high rate of self-discharge, which limits their long-term operation. Bobbin-type cells have the ideal capacity and energy density, but have two main drawbacks: severe passivation problems after storage at elevated temperatures, and low current due to its low rate design.
To overcome these obstacles, engineers at Tadiran developed a hybrid lithium battery called PulsesPlus™ which combines a bobbin-type primary cell with a patented high rate, low impedance HLC (hybrid layer capacitor).
This hybrid system delivers extremely high currents with an excellent safety margin. This is accomplished simply because the HLC can store up to 700 Wh/Kg of energy. The rate at which energy can be stored by the HLC varies from 280 A/Sec. with smaller HLCs, to 1,120 A/Sec. with larger size HLCs.
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