contrary to popular misconception,
lithium batteries are not created equal

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 arena, LiCFX (poly carbon monofluoride) and LiMN02 (manganese dioxide) are found in cameras, calculators and watches. In the military arena, LiSO2 (sulfur dioxide) batteries are used in high power radios. LiSOCl2 (thionyl chloride) and LiI2 (lithium iodine) are commonly utilized in industrial and medical applications.

LiCFX 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 LiCFX cells in terms of construction and problems with high temperature and humidity. Their energy density and voltage is slightly better than LiCFX cells, especially at cold temperatures.

 

LiSO2 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. Their main drawback also results 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 LiSO2 cells are typically less than half that of lithium thionyl chloride cells.

 

LiSOCl2-- 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 40 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 (AEDs) that must be ready for use at all times without risk of battery failure.

 

 

Bobbin-type vs. Spirally Wound

 

Two types of lithium thionyl chloride cells are available: bobbin and spirally wound construction. With both versions, the non-aqueous electrolyte results in relatively high impedance. One way to solve this impedance problem is to increase the surface area by going to a wound cathode. Unfortunately, this solution is not without cost. The drawbacks to spirally wound construction include reduced energy density (you now have more inactive material within the cell) and shorter operating life (extra surface area results in a higher self-discharge rate).

 

Bobbin-type LiSOCl2 cells are particularly well suited for low-current applications due to their high energy density, very low self-discharge rate, and up to 40-year operating. Bobbin-type lithium thionyl chloride cells also offer an extended temperature range from -55°C to +125°C. High capacity, small size, and an ability to withstand broad fluctuations in pressure, temperature and shock make bobbin-type LiSOCl2 cells ideal for use in remote locations and extreme environments.

 

 

High current pulse "hybrid" solutions

 

A growing number of applications require high current pulses, presenting technical challenges to both spirally wound and bobbin-type lithium batteries. Typically, these applications involve low continuous current (or no continuous current) coupled with high pulse currents of up to several Amperes for a period of seconds up to 20 minutes.

 

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, Tadiran developed a hybrid lithium battery called PulsesPlus™ that 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 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.

 

 

Tadiran engineers solutions for extreme environments

 

Recognized globally as a leading source for lithium batteries, Tadiran is continually looking to improve its innovative lithium battery technology. Working closely with customers and government research organizations, Tadiran is  committed to developing new lithium battery technologies that enhance the performance capabilities of industrial grade batteries.

 

Our chemists and engineers are continuously developing new product  innovations to meet and exceed the needs of our customers…now and in the future.

 

RElated articles

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Combining low-power communications protocols with long-life lithium batteries (as appeared in ZigBee Resource Guide)

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