Lithium sulfur dioxide battery

The lithium-sulfur dioxide battery is a non-rechargeable lithium battery with lithium as the anode and an inert electrode ( carbon black - Teflon mixture on a metal mesh) as the cathode , the sulfur dioxide being reduced cathodically. Acetonitrile with lithium bromide as the conductive salt is mainly used as electrolyte and solvent for sulfur dioxide . Inside the battery there is a pressure of up to 4 bar due to the vapor pressure of sulfur dioxide, depending on the temperature  . This type of battery was one of the first technically used lithium batteries and was developed in 1938. It is characterized above all by a wide operating temperature range from −55 ° C to +70 ° C and low self-discharge with a comparatively good energy density.

properties

The open circuit voltage of the battery is 3.0 V and the typical load voltage is 2.7 V. The very flat discharge curve can be increased to approx. 3.9 V by adding bromine chloride . The practically achievable energy density for cylindrical round cells is 400–450 mWh / cm ³ . The self-discharge is approx. 0.16 percent / month. Types from 0.9 to 13 Ah are produced as sizes, button cells do not exist for this battery type.

Due to the high pressure of sulfur dioxide inside the battery, there is a risk of the housing exploding in the event of an electrical short circuit or at high temperatures such as a fire. The acetonitrile used as the conductive salt forms the very toxic hydrogen cyanide at high temperatures . Furthermore, the production costs per cell are comparatively high. For these reasons, lithium-sulfur dioxide batteries are primarily only used for certain industrial and, in particular, military purposes, such as emergency radio beacons , where low self-discharge and the wide temperature range are important.

Electrochemistry

During the discharge process, lithium is anodically oxidized to lithium ions (Li ⁺ ), releasing electrons . Sulfur dioxide is several reaction steps and radicals formed in the meantime to cathodic dithionite reduced . The overall equation can be formulated as follows:

${\displaystyle \mathrm {2\ Li+2\ SO_{2}\rightarrow Li_{2}S_{2}O_{4}} }$

Donor half-cell : ${\displaystyle \mathrm {2\ Li\longrightarrow 2\ Li^{+}+2\ e^{-}} }$

Acceptor half cell : ${\displaystyle \mathrm {2\ SO_{2}+2\ e^{-}\longrightarrow S_{2}O_{4}^{2-}} }$

The poorly soluble lithium dithionite Li ₂ S ₂ O _{4 formed} is deposited in the pores of the cathode and, due to the additional polarization voltage, increases the resistance of the cell.

literature

• Günter Eichinger, Günter Semrau: Lithium batteries II - discharge reactions and complete cells. In: Chemie in our Zeit 24, No. 2, ISSN  0009-2851 , 1990, pp. 90-96.

Web links

• USPHC Managing Lithium Sulfur Dioxide Batteries (PDF; 40 kB)
• Fraunhofer ICT: Description of the lithium-sulfur dioxide battery

Individual evidence

1. ↑ Ivan Cowie: All About Batteries, Part 10: Lithium Sulfur Dioxide (LiSO2). Retrieved February 26, 2019 .