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What is the battery of the heat battery? How does the heat battery work?
**What is a Thermal Battery?**
A thermal battery, also known as a heat battery, is a type of primary reserve battery that is activated by heating. It uses molten salt as an electrolyte, which becomes conductive when melted. This makes it ideal for applications where high energy density, long shelf life, and reliable performance under extreme conditions are required. Due to its ability to operate across a wide temperature range, compact design, and low maintenance, it has become a key power source in military technology, especially for missiles, artillery, and nuclear weapons.
Early thermal batteries were based on cup-shaped structures, with cathodes made of materials like WO3 or V2O5, and anodes made of calcium or magnesium. The electrolyte was usually a LiCl-KCl eutectic mixture soaked into glass cloth, while the ignition material was often Zr-BaCrO4 paper. These early designs had issues such as short discharge times, complex construction, and significant electrical noise, limiting their practical use.
In the 1960s, the Ca/CaCrO4 thermal battery introduced a more advanced sheet structure, using LiCl-KCl as the electrolyte and Fe/KClO4 as the heating agent. This improved the battery's performance, simplified manufacturing, and extended its operational life, although electrical noise remained a challenge.
By the 1970s, the LiMx/FeS2 thermal battery (where LiMx is a lithium alloy) marked a major breakthrough. It not only reduced electrical noise but also significantly increased specific energy and power, making it one of the most advanced thermal battery systems available today. This development set the stage for modern thermal battery technology.
China began developing thermal batteries in the 1970s, catching up quickly with global advancements. By the 1980s, the country had made significant progress, producing various models that were successfully used in military applications. Today, LiMx/FeS2 thermal batteries are among the preferred power sources for new weapon systems, with a competitive and well-established production system in place.
**How Do Thermal Batteries Work?**
Thermal batteries are thermally activated primary reserve batteries. They typically consist of multiple single-cell units connected in parallel, along with a heating sheet, all enclosed in a protective casing. The battery’s stack is connected to the terminal via a drain bar, and the entire unit is sealed using argon arc welding.
Each cell includes a positive electrode, an electrolyte, and a negative electrode, with a heating sheet at both ends. When the battery is needed, an external signal or mechanical trigger ignites the internal igniter, activating the heating system. This raises the temperature of the cell to around 400–600°C, melting the solid electrolyte into a conductive liquid. At this point, electrochemical reactions between the electrodes begin, generating electricity.
Once connected to an external circuit, the battery enters its working state. The lifespan of a thermal battery depends on two factors: electrical life and thermal life. Electrical life refers to how long the battery can deliver power within a certain voltage range, while thermal life relates to how long the battery can maintain its operating temperature. When the active materials are consumed or the temperature drops below the electrolyte’s freezing point, the battery stops functioning.
The operation of a thermal battery involves two main stages: activation and discharge. During activation, the battery rapidly heats up from room temperature to about 550°C. Once activated, it begins discharging, and the internal temperature gradually decreases. As the temperature drops, the electrolyte’s ionic conductivity weakens, increasing the internal resistance. Eventually, the electrolyte solidifies, ending the battery’s operational life.