The lithium thionyl chloride (Li-SOCl2) battery

This specific type may have a liquid cathode, suitable for temperatures as low as -55°C, which puts it firmly in the category suitable for low-temperature performance. Unlike other battery technologies using liquids that produce a gas by-product, this technology is very good, with limited emissions even under abusive conditions. Unfortunately, the electrolyte is toxic and reacts with water.

The battery has a high specific energy and low weight, but makes sacrifices for a very high internal resistance, and therefore has a low-rate-only discharge with limited short-circuit current. An additional concern is that, following long-term storage, the battery exhibits a delay in producing a good terminal voltage when finally put into service. At least one company has compensated for some of these shortcomings by including a capacitor inside the package.

Very low-current versions of this technology find use in battery backup for memories and remote monitoring-metering, while higher-current versions are used in some military and automotive applications. Safety concerns (such as explosion and its Class 9 Hazmat shipping classification) and high cost have prevented more widespread use of this technology. 

• Specific energy: approximately 500 Wh/kg
• Energy density: approximately 1200 Wh/L
• Specific power: approximately 18 W/kg
• Discharge efficiency: 6 to 94 % (highly dependent on load)
• Energy/consumer-price: 5.1 Wh/dollar
• Self-discharge rate: 0.08 %/month
• Cycle durability: (primary battery)
• Nominal cell voltage: 3.5V typical (3.65V new, open circuit)
• Cut-off voltage: 3 volts per cell, loaded
• Temperature range: -55 to +85°C typical (some specialty types up to +130°C)

Chemistry
4Li + 2SOCl₂ → 4LiCl + S + SO₂

The following images illustrate some interesting characteristics associated with lithium thionyl chloride batteries:

Figure 1. Half AA size, Blue curve=180K Ohms for four years. Grey curve=180 Ohms for 30 hours. Zoom circles are closeup of voltage recovery whenever the discharge is interrupted.

Figure 2. Voltage delay effect, terminal voltage verses time.

Figure 3. Dependence of capacity on current -- self-discharge increases with operation life.

Figure 4. Terminal voltage and internal resistance with depth of discharge for two load types.