Thermal Battery Technology: How It Works and Where It’s Used

Thermal battery technology offers an innovative way to store energy and tackle challenges in power demand. This technology captures excess heat and converts it back to electricity or heating. Thus, thermal battery technology balances the intermittent nature of renewable energy sources with constant electricity demand. Let’s explore how exactly this technology works!

What is a Thermal Battery?

A thermal battery is a thermal storage system that captures and stores heat for later use. It uses a storage medium that absorbs and releases heat during phase changes or temperature variations.

Thermal batteries offer high density. They can be stored for years without performance degradation.

Before discussing thermal batteries in detail, let’s recall that heat batteries have been used for thousands of years as thermal energy storage systems! A house with thick walls can be considered a passive thermal battery. Walls absorb and store heat from sunlight or internal heating sources during the day and release it during cooler periods. This helps maintain a more stable indoor temperature without additional input. The walls don’t store energy like a traditional battery but still store thermal energy, making the house a passive thermal battery. Thermal batteries replace or supplement existing natural gas boilers in industrial plants for heating needs.

Thermal management of these devices differs from EV Battery Thermal Management because thermal batteries focus on storing and releasing heat rather than maintaining a narrow operational temperature range to protect electrochemical reactions, as in EV batteries.

Thermal batteries are made with materials that can absorb and store heat well, such as graphite, crushed rock, and bricks. Companies like Rondo Energy develop thermal batteries using conductive bricks that can heat to high temperatures for industrial applications.

How Does Thermal Battery Technology Work?

Thermal batteries’ unique design and chemistry make them ideal for scenarios requiring long shelf life, rapid activation, and reliable performance under extreme conditions. Let’s see how this works.

Thermal battery technology operates based on stacked electrochemical cells arranged in series or parallel configurations, depending on the desired power density and volume. For compact designs, a thermal battery may contain a single series stack of cells or multiple parallel stacks for applications requiring higher energy outputs.

Four components are present in cells:

N°1: The Cathode acts as an electron acceptor during discharge.

N°2: The Electrolyte is a solid-state material that conducts ions between the anode and cathode.

N°3: The Anode functions as the electron donor.

N°4: The Pyrotechnic Heat Source provides the thermal energy required to melt the electrolyte, activating the battery. This feature allows the battery to transition from dormant to active within milliseconds. “Pyrotechnic” is a controlled chemical composition that burns rapidly to produce heat.

Modern thermal batteries utilize advanced chemistry, such as the lithium silicon/iron disulfide (LiSi/FeS₂) couple, which offers four advantages: 

• High Density: LiSi/FeS₂ provides one of the highest capacities per unit volume, enabling compact designs without sacrificing performance. 
• Substantial Power Density: The chemistry allows for rapid delivery, which is crucial for applications requiring immediate power. 
• Low and Stable Internal Impedance: The battery maintains consistent internal resistance during operation, ensuring reliable performance and high efficiency. 
• Environmental Adaptability: These batteries are resilient and function effectively across various temperatures and pressures, making them suitable for demanding environments like aerospace and military applications.

A Little Bit of Physics of Thermal Batteries

A thermal battery stores heat in a storage medium and releases it when needed. It stores heat by warming up and sometimes melting a medium, and it releases it by cooling down and sometimes solidifying.

The amount of heat stored depends on three key factors:

1. Weight: A heavier medium can accumulate more.

2. Heat-holding ability: Water or special salts can hold more heat per kilogram.

3. Temperature range: The bigger the range between when the heat storage and heat release is released, the more it can accumulate.

These types of batteries are usually designed with the help of thermal modeling tools, similar to heat exchanger design software.

Types of Thermal Batteries

In this section, we will shortly review the main types of thermal batteries.

Phase Change Thermal Battery

Batteries absorb and release thermal energy during melting and solidification. Their advantages include high energy density, stable operations, compact size, and applicability in renewable power or industrial settings. Solar storage is an example of this, as it can be used for nighttime heating or off-grid electricity generation.

Molten Salt Thermal Battery

Molten salt systems utilize high-melting salts, efficiently recovering waste heat and storing solar thermal energy. They are employed in concentrated solar power plants to store excess heat during the day and generate electricity at night or during cloudy periods. Due to their thermal stability and high heat capacity, these systems are suitable for high-temperature applications, such as industrial processes and combined heat and power. Additionally, they are chemically stable and non-flammable, enhancing safety in large-scale, high-temperature operations.

Sensible Heat Thermal Battery

Sensible heat thermal batteries store energy by raising the temperature of a solid or liquid without changing its power density or phase. Common mediums include water, oil, and concrete.

Their advantages include simple design, low cost, and inexpensive and readily available materials. The technology is easy to implement and requires minimal maintenance. An example application is building heating systems, where water or concrete absorbs heat during the day and releases it at night to provide indoor comfort.

Thermochemical Thermal Battery

Thermochemical batteries are based on reversible chemical reactions such as A + Heat ⇌ B + C.

The advantages are high density, long-term storage without loss, and suitability for transportable and seasonal usage. Heat remains stored  until a reverse reaction is triggered! Thus, hydrogen-based setups use reversible chemical reactions to capture thermal input and release it later for industrial applications or electricity generation.

Applications of Thermal Batteries

This section reviews key applications of thermal batteries, particularly in renewable electricity. Thermal batteries store excess thermal energy from renewables, ensuring a consistent supply when production dips.

Industrial Processes

Thermal batteries recover waste heat in industrial facilities. They capture heat from steel manufacturing or chemical production, storing it for preheating materials, generating steam, or powering other processes, boosting efficiency and lowering costs.

A real-world example is using thermal batteries in steel plants to store heat from hot exhaust gases during steel production. The batteries can later be used to preheat incoming raw materials or generate steam for turbines, significantly reducing the need for burning fossil fuels.

Military and Aerospace Applications for Thermal Battery

Thermal batteries have supported military and aerospace applications for decades, especially where long shelf life and reliability are essential. They provide a maintenance-free solution that activates quickly after dormancy. Their high power density and rapid activation are advantageous. For example, the battery remains inactive in missile guidance systems until launch, then supplies reliable, immediate power to critical electronics, ensuring operation under extreme conditions.

Grid Stabilization and Load Leveling

Thermal batteries stabilize the electrical grid by storing excess energy during low demand and releasing it during peak demand. They can be integrated into heating and cooling systems, storing heat during off-peak hours and releasing it during high demand, which helps reduce strain on the grid.

A real-life example of thermal batteries stabilizing the electrical grid is large-scale thermal energy storage in Denmark’s district heating systems. Denmark has pioneered Pit Thermal Energy Storage with Solar District Heating for seasonal use. This system stores excess thermal energy generated during low demand for later use during peak times, reducing grid strain. It enhances efficiency and aids the decarbonization of heating.

Differences between a Thermal Battery and an EV Battery

Thermal and EV batteries both store energy but serve different functions.

Thermal batteries store thermal energy for industrial heating, managing excess heat in processes such as manufacturing or balancing energy during intermittent renewable generation. They contribute to the energy transition by improving efficiency and reducing reliance on fossil fuels in heating and industrial processes, potentially helping lower industrial emissions. On the other hand, EV batteries store electrical energy to power electric vehicles, supporting the shift towards cleaner transportation. The US Department of Energy (DoE) is exploring integrating such systems for greater energy efficiency. While thermal batteries and EV batteries are distinct technologies, both are essential to achieving sustainability goals. Future synergies could further enhance their role in reducing emissions and optimizing energy use across industries.

Another difference is, for example, the cooling techniques used to maintain operational efficiency and safety. Thermal batteries rely on passive systems such as insulation, while EV batteries rely on active systems such as immersion cooling.

Advantages and Challenges Thermal Batteries

Let us briefly review the main advantages of thermal batteries.

Challenges and Future Prospects

What are the main challenges and opportunities for thermal batteries and storage? 

• Material Optimization. The performance of thermal batteries depends on materials and design. Research focuses on materials with higher thermal capacity and optimizing heat transfer fluids.
• Integration with Technologies. Integrating thermal batteries with current systems offers both opportunities and challenges.
• Market Adoption and Support. Green policies can speed up deployment and innovation for thermal battery technology to succeed in this sector.

Conclusions

Thermal batteries balance intermittent energy generation (solar or wind) with consistent energy demand by employing thermal energy storage solutions. These systems are cost-effective across various applications and efficiently store excess thermal energy generated during periods of low demand, which can later be used when demand peaks.

Thermal batteries’ advantages include their scalability, long lifespan, and low cost. These make them suitable for energy storage in residential heating systems for large-scale industrial applications. These benefits position them as a potential solution for enhancing grid stability, improving efficiency, and supporting clean energy integration.

However, challenges like optimizing materials, enhancing design, and boosting operational efficiency still hinder widespread adoption. Continuous research is essential to refine thermal storage technologies, improve heat retention, and tackle response time and thermal loss issues so that they can realize their full potential.

FAQs

How efficient are thermal batteries?

Thermal batteries are highly efficient, with minimal loss over time, especially when using phase change techniques.

What is the best material for a thermal battery?

Common materials include phase change materials, salts, water, and concrete, depending on the application.

Who are the leading thermal battery manufacturers?

EaglePicher Technologies, Saft, and Tadiran provide high-performance, reliable energy storage solutions for military, aerospace, and industrial applications.

What are the disadvantages of thermal batteries?

Thermal batteries can require high temperatures and specialized infrastructure, which can limit their applications and increase costs.

How long do those batteries last?

Depending on the thermal conductivity and the specific heat capacity, it can last from hours to days.

What are the environmental benefits of thermal batteries?

Thermal batteries help reduce carbon emissions by enabling the efficient storage and use of renewable energy sources, such as solar and wind, and by optimizing industrial heating and manufacturing processes. Their capability to store excess energy during off-peak hours and release it when necessary reduces reliance on fossil fuels, making them a sustainable energy solution.

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