How To Solve The Problem of Insufficient Pulse Discharge Capability in Lithium Thionyl Chloride Batteries?

Introduction

Lithium thionyl chloride (Li-SOCl₂) batteries are widely recognized for their exceptionally high energy density, ultra-low self-discharge rate, and long service life. These characteristics make them ideal for applications such as smart utility meters, IoT devices, asset tracking systems, industrial sensors, military equipment, and remote monitoring systems.

However, despite their many advantages, lithium thionyl chloride batteries have one well-known limitation: poor pulse discharge capability. While these batteries perform exceptionally well under low continuous current loads, they often struggle to supply the high current pulses required by modern electronic devices.

This article explores the reasons behind this limitation and the most effective methods for improving the pulse discharge performance of lithium thionyl chloride batteries.

What Is Pulse Discharge?

Pulse discharge refers to the battery's ability to deliver a relatively large current for a short period of time.

Examples include:

• Wireless data transmission

• GSM/GPRS communication modules

• LoRa and NB-IoT devices

• GPS positioning systems

• Remote monitoring equipment

• Alarm systems

• Smart metering data uploads

A device may consume only a few microamps or milliamps most of the time, but suddenly require hundreds of milliamps or even several amperes during transmission.

For example:

This short-term high-current demand is known as a pulse load.

Why Do Lithium Thionyl Chloride Batteries Have Limited Pulse Capability?

1. Bobbin-Type Structure

Most standard Li-SOCl₂ batteries use a bobbin construction.

Advantages:

• Very high capacity

• Long service life

• Low self-discharge

Disadvantages:

• High internal resistance

• Limited current output

Typical examples:

• ER14250

• ER14505

• ER18505

• ER26500

• ER34615

These batteries are optimized for long-term low-current applications rather than high-power output.

2. Passivation Effect

A unique characteristic of lithium thionyl chloride batteries is the formation of a passivation layer on the lithium anode.

This layer helps achieve:

• Extremely low self-discharge

• Shelf life exceeding 10 years

However, passivation also causes:

• Increased internal resistance

• Temporary voltage delay

• Reduced pulse performance

When a large current is suddenly demanded, the battery voltage may drop significantly before recovering.

3. High Internal Resistance

Compared with lithium-ion batteries, Li-SOCl₂ batteries naturally have higher internal resistance.

Consequences include:

• Voltage sag during pulse loads

• Reduced effective power output

• Inability to support communication modules directly

This is one of the primary challenges in IoT and telemetry applications.

Common Symptoms of Insufficient Pulse Capability

When pulse current requirements exceed the battery's capability, users may observe:

• Communication failures

• Device resets

• Voltage drop alarms

• Unstable operation

• Reduced battery utilization

• Shortened service life

In severe cases, devices may appear to have a depleted battery even though substantial capacity remains.

Solution 1: Use a Hybrid Capacitor (HLC)

One of the most effective solutions is combining the battery with a Hybrid Layer Capacitor (HLC).

How It Works

The battery supplies:

• Low continuous current

The HLC supplies:

• High pulse current

The capacitor stores energy slowly from the battery and releases it rapidly when needed.

Advantages

• Excellent pulse performance

• Reduced voltage drop

• Longer battery life

• Improved communication reliability

Typical Applications

• Smart gas meters

• Smart water meters

• Smart electricity meters

• NB-IoT devices

• LoRaWAN sensors

This is currently one of the most widely adopted solutions in the metering industry.

Solution 2: Add a Supercapacitor

A supercapacitor can also be connected in parallel with the battery.

Benefits

• Delivers very high peak currents

• Compensates for battery voltage sag

• Supports wireless communication bursts

Typical Capacitor Values

• 0.1F

• 0.47F

• 1F

• 10F

Selection depends on pulse duration and current requirements.

Example

A battery may provide:

• Continuous current: 10mA

A supercapacitor may supply:

• Pulse current: 1A

for several hundred milliseconds.

Solution 3: Use Spiral-Type Li-SOCl₂ Batteries

Unlike bobbin-type cells, spiral-type lithium thionyl chloride batteries are specifically designed for high-current applications.

Advantages

• Lower internal resistance

• Higher pulse capability

• Faster voltage recovery

Examples

• Saft LSH20

• Saft LSH14

• Tadiran PulsesPlus series

• EVE Spiral Series

Performance

Pulse currents can reach:

• Several amperes

• Tens of amperes in some cases

Trade-Off

Compared with bobbin cells:

• Lower capacity

• Higher self-discharge

• Higher cost

Solution 4: Use a Battery Capacitor Combination Pack

Many industrial battery packs combine:

• Li-SOCl₂ battery

• HLC

• Protection circuitry

into a single integrated solution.

Advantages

• Simplified installation

• Optimized performance

• Longer service life

• Improved reliability

This approach is common in industrial IoT and smart metering projects.

Solution 5: Optimize Device Power Consumption

Sometimes the issue can be addressed at the device level.

Strategies

• Reduce transmission frequency

• Shorten communication duration

• Optimize firmware

• Lower startup current

• Use energy-efficient communication protocols

Example

Instead of transmitting every minute:

• Transmit every 15 minutes

This significantly reduces pulse load requirements.

Solution 6: Reduce Passivation Through Proper Usage

Passivation can become more severe during long storage periods.

Methods to Reduce Passivation

• Perform periodic low-current discharge

• Use pulse conditioning circuits

• Avoid extremely long storage at elevated temperatures

• Select batteries designed for pulse applications

These measures help maintain lower internal resistance over time.

Solution 7: Select Batteries with Pulse-Optimized Designs

Several manufacturers offer specialized Li-SOCl₂ batteries designed specifically for pulse applications.

Examples include:

• Tadiran PulsesPlus

• Saft Xeno Energy series

• EVE ER+HLC solutions

• Fanso Pulse Series

These products incorporate optimized chemistry and capacitor technology to improve pulse performance significantly.

Choosing the Right Solution

The most suitable solution depends on the application's pulse current requirements.

Typical Application Examples

Smart Water Meter

Requirements:

• Sleep current: 5μA

• Transmission pulse: 200mA

Recommended:

• ER14505 + HLC

NB-IoT Tracker

Requirements:

• Average current: 50μA

• Transmission pulse: 1A

Recommended:

• ER26500 + Supercapacitor

Emergency Locator Beacon

Requirements:

• High-power RF transmission

Recommended:

• Spiral-type Li-SOCl₂ battery

Future Development Trends

As IoT technology continues to evolve, manufacturers are developing new solutions to improve pulse performance, including:

Advanced Hybrid Capacitors

Higher energy density and longer lifespan.

Lower Resistance Electrolytes

Improved current delivery capability.

Integrated Battery-Capacitor Modules

Simplified system design and enhanced reliability.

Smart Power Management Circuits

More efficient energy utilization and pulse control.

These innovations will further expand the application range of lithium thionyl chloride batteries.

Conclusion

Although lithium thionyl chloride batteries offer exceptional energy density, long shelf life, and ultra-low self-discharge, their pulse discharge capability is often limited by high internal resistance and passivation effects. Fortunately, this challenge can be effectively addressed through various methods, including the use of hybrid layer capacitors (HLCs), supercapacitors, spiral-type cells, battery-capacitor packs, and optimized device power management.

By carefully matching the battery solution to the application's pulse current requirements, engineers can achieve both long service life and reliable high-current performance, making lithium thionyl chloride batteries an excellent choice for modern industrial and IoT applications.