Lithium thionyl chloride batteries are primary batteries. This means they produce electricity through a non-reversible chemical reaction. So why is lithium thionyl usually not rechargeable?
Their Operation Depends On Lithium Metal At Negative
Their operation depends on lithium metal at the negative electrode and thionyl chloride as the liquid cathode material and electrolyte. During discharge, lithium is oxidised, releasing electrons that travel through the external electrical circuit.
At the positive electrode, the thionyl chloride participates in the reduction reaction. The overall reaction produces electrical energy, together with lithium chloride and sulphur-containing compounds.
Why Is Lithium Thionyl Chloride Chemistry Not Reversible?
In a rechargeable battery, the chemical reactions must be sufficiently reversible to allow the original active materials to be restored during charging. Lithium thionyl chloride chemistry does not provide this reversibility in its conventional commercial design.
Attempting To Recharge Causes Unwanted Chemical Reactions
Attempting to recharge an ordinary lithium thionyl chloride cell can cause unwanted chemical reactions. These include gas generation, internal pressure and potentially dangerous failure.
It is therefore essential never to connect one to a conventional battery charger. This is whylithium thionyl usually not rechargeable.
Another Interesting Feature Is Passivation
Another interesting feature is passivation. When a lithium thionyl chloride battery is stored, a thin lithium chloride layer forms on the surface of its lithium electrode. This layer helps prevent unwanted reactions and greatly reduces self-discharge.
This Is Beneficial Because It Allows The Battery To Retain
Passivation is beneficial because it allows the battery to retain its energy during long periods of storage. However, it can temporarily increase internal resistance when the battery is first used, causing a voltage delay under certain loads.
Researchers Continue Investigating Ways To Improve
Researchers continue investigating ways to improve this chemistry. A 2023 study reported that adding iodine to the electrolyte could improve discharge performance and make rechargeable operation possible under experimental conditions.
This research is scientifically interesting, but it does not mean ordinary commercial lithium thionyl chloride batteries have become rechargeable.
These Batteries Should Always Be Single-Use
For practical purposes, these batteries should always be treated as single-use power sources. Once exhausted, they must be replaced and disposed of or recycled through an appropriate battery-handling system.
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