Lithium thionyl chloride battery

The lithium thionyl chloride battery is a non-rechargeable lithium battery with lithium as the anode and a graphite electrode as the cathode , the thionyl chloride being reduced cathodically and serving as a solvent and electrolyte at the same time .

properties

Scheme of a lithium thionyl chloride battery (cylindrical shape)

The open-circuit voltage of the battery is 3.7 V and the typical load voltage is 3.4 V. Due to this favorable cell voltage compared to other lithium batteries and due to the low self-discharge , this type of battery has a difference compared to other oxyhalides such as phosphorus oxychloride (POCl ₃ ) or sulfuryl chloride (SO ₂ Cl ₂ ) enforced. The energy density for button cells is approx. 700 mWh / cm³ and the self-discharge is 0.08 to 0.16% / month, or 1–2% / year with a shelf life of 10 years.

Electrochemistry

During the discharge process, lithium is anodically oxidized with the release of electrons to lithium ions (Li ⁺ ), which react to lithium chloride . Thionyl chloride is cathodically reduced to elemental sulfur in several reaction steps , with sulfur dioxide being formed at the same time . The overall equation can be formulated as follows:

${\displaystyle \mathrm {4\ Li+2\ SOCl_{2}\rightarrow 4\ LiCl+S+SO_{2}} }$

The cathodic reaction products are deposited in the pores of the highly porous carbon electrode. Sulfur dioxide partially dissolves in the electrolyte. The anodic lithium chloride is deposited in crystalline form on the lithium and forms a protective film that protects the lithium from attack by the solvent and thus reduces self-discharge.

The electrolyte thionyl chloride also contains a conductive salt, especially lithium tetrachloroaluminate (LiAlCl ₄ ).

literature

• Günter Eichinger, Günter Semrau: Lithium batteries II - discharge reactions and complete cells. In: Chemie in our Zeit 24, No. 2, 1990, pp. 90-96, doi: 10.1002 / ciuz.19900240209 .