BATTERIES

# Lithium Thionyl Chloride

## Overview

Lithum thionyl chloride batteries are good for long-term power applications such as wireless remote sensors, backup power for non-persistant memory ICs, and real-time clocks.

## Voltage

Lithium thionyl chloride batteries have a nominal voltage of 3.6V.

## Current Draw

This is where Lithium thionyl chloride batteries show their weakness. They are really bad at providing large pulse currents, due to their high internal resistance. This can make the batteries bad at powering pulse-current drawing things like cellular modems. You can add super-capacitors to provide the pulse current in some applications. Some manufacturers have begun selling a combined battery/supercap module which allows for higher pulse currents.

## Leakage Current

Lithium thionyl chloride batteries have a really low leakage current.

## Discharge Characteristics

They have a pretty flat voltage discharge characteristic.

## Energy Density

They have an energy density of 970mWh/cm^3 (when the discharge current is 100uA).

## Temperature Range

They can be used over a wide temperature range of $$-55^\circ C$$ to $$+85^\circ C$$.

## Chemical Reaction

Lithium thionyl chloride batteries use liquid thionyl chloride ($$SOCl_2$$ as the positive active material, and lithium (Li) as the negative active material.

Note that the following table describes the reactions for discharging, the reactions occur in the opposite direction when the battery is recharging.

 Positive Reaction: $$2SOCl_2 + 4Li^+ + 4e^- -> 4LiCl + S + SO_2$$ Negative Reaction: $$Li -> Li^+ + e^-$$ Combined Reaction: $$2SOCl_2 + 4Li -> 4LiCl + S + SO_2$$