ASB Thermal Battery: The Power of Reliability

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A Review of Advances in Thermal Battery Technology

New generations of Aeronautic systems demand high power capabilities, even for miniaturised defence systems. The modern power source requires being more robust to cope with higher velocity and environmental conditions, more reliable due to the high costs of modern systems, have more design optimisation due to specific constraints and have a longer storage life to reduce life cycle costs. Among primary battery solutions, the thermal battery features unexploited benefits for innovative applications. Thermal batteries have been traditionally used in defense applications; they are now utilized in other domains which require reliability and performance under harsh environments.

Technology to Your Advantage

A thermal battery is a unique reserve primary battery, the name of which might appear misleading. A thermal battery provides its power not by converting thermal energy to electrical energy, but from a reactive electrochemical couple. The operating principle of a thermal battery is simple compared to typical reserve batteries in which liquid electrolyte has to be stored and transferred before use when the battery is activated. Thermal battery cells contain an electrolyte which is solid and non-conductive under normal temperature conditions and a heat source which produces sufficient energy to melt the electrolyte when activated. Once melted the electrolyte becomes highly conductive and allows the battery to discharge. Discharge is either terminated by exhaustion of the cell materials or by solidification of the electrolyte by cooling.

Consequently, the operational advantages of the thermal battery are:

• The very long shelf life in a ready state without degradation in performance.
• “Instant” activation: fast start designs can provide useful power in fractions of a second, crucial for applications such as ejection seats.
• Totally inert until activated satisfying the most severe safety standards.
• Very high Specific Power (W/kg).
• Very high demonstrated reliability and ruggedness following long-term storage over a wide temperature range and severe dynamic environments: current data puts battery reliability at around 99.98% at a confidence level of 95%.
• No maintenance required: can be permanently installed in equipment.
• No self-discharge: before activation a thermal battery has practically no output.
• Wide operating temperature range, No outgassing: the battery is hermetically sealed, Custom designed for specific voltage, start time, current and physical configuration requirements.
• Totally safe in operation: thermal batteries are classified as non-explosive and non-pyrotechnic for transportation & storage.

What is not so well known is the important field of technology research results in steadily increasing performances of thermal batteries. Every aspect is researched: better understanding of physical phenomena, enhanced methods for battery designs optimisation, experimental and computational tools, new materials for the anode (lithium derivatives) and for the cathode (new sulfides more thermally stable than pyrite, etc.). For the electrolyte, new binders, new manufacturing techniques for thinner cells production, new materials and designs for the thermal insulation, etc.

The general distinction of thermal battery technology is related to the type of anodes. From an electrochemical point of view, lithium is the most valuable element due to its high reducing potential and its high specific coulombic capacity.  As its melting point is lower than the thermal battery operating temperature, alloyed forms are used such as Li/Al (Lithium Aluminium), LiSi (Lithium Silicon) or a lithium-iron mixture, named LAN (Lithium Anode, an exclusive ASB technology). For very specific applications calcium anodes may also be used.

Each technology has its particular advantages: calcium is associated with very fast activation, for instance in ejection seats, while Li-Si offers high electro-motive force and would preferably be selected for high voltage but low energy batteries. Li/Al represents a cost-effective optimum down to very small batteries. At the other end, LAN technology is the most suitable solution for high capacity, high current density and high robust cases. It is therefore the appropriate electrochemistry for the new generation of high power batteries, for application fields such as underwater systems, decoys and sono-buoys. It is also used in emergency power supplies in UAVs and fighter aircrafts, as well as space actuator systems.

None of these individual technologies could offer a universal solution for a specific application. Therefore the ASB-Group have developed a vast resource of experience and expertise in all of them in order to provide the customer with an appropriate combination to meet his specific requirements. Combined with the extensive use of our predictive thermal battery model, our technology range is guaranteed to provide an optimal custom design.

New Power for New Applications

The most promising area of research concerns the extension of the specific power and energy of the thermal battery. With extensive use of the predictive electro-thermal model “Ether” combined with the on-going innovation in manufacturing processes and material technologies, the ASB-Group can offer advanced solutions with a higher specific energy density. The Specific Energy Density has been multiplied by 4 over the last 10 years: performance of in-production designs is up to 120Wh/kg, and 160Wh/kg at cell level. The use of pure lithium (LAN) has reduced the size of the batteries to as much as one-tenth of earlier designs using lithium alloys.

In conjunction with inherent improvement of the thermal battery technology, this widening of the performance range responds to new demanding applications. For instance, thermal battery solutions are now replacing several old generation batteries on board large missiles and torpedoes. The ability to provide several output voltages from the same battery allows a reduction in the number of batteries required. Thanks to the longer operating duration (more than one hour) as well as low internal impedance due to LAN electro chemistry, some thermal batteries can now power both electronics and actuators.

Another field of interest is the high voltage power supply. Thermal batteries can be connected in series and parallel in battery sets. An important rising demand is focused on power supplies for Thrust Vector Control (TVC) and actuation system of exhaust nozzles, for large missiles and space launchers. The key features are the robustness of the thermal battery solution, their compatibility with high pulse regime and reverse charging, their reliability and their price.

At the other extreme end of the battery range, ASB-Group have developed a miniaturised “smart” battery family, primarily dedicated to new artillery applications. By combining innovative manufacturing processes and new electro chemistries, a power output of 2 watts is now available from a volume of around 1.5cc. This battery activation can be autonomous, thanks to percussion mechanisms that can be fitted within the battery. This built-in striker mechanism is designed to operate under the launch acceleration shock, while remaining insensitive to the full transportation and handling conditions. The fully integrated power supply within the artillery shell can thus be stored without any limitation for years and supply the required power at launch initiation without any external connections. This technology is particularly well suited to the requirements of modern battlefield equipment. It is dedicated to equip proximity fuses, safety and arming units, dropped sensors, smart munitions, grenades and other embarked micro-systems.

The Power of Reliability

Great strides have been made in improving the thermal battery technologies: various electro chemistries are now available in order to provide custom designed solutions to meet any type of requirements. The intensive use of the predictive model “Ether” allows the finest selection and design tuning. This expertise of the European leader ASB-Group is now offered to the Indian market.

Thermal Batteries’ intrinsic advantages make them ideal solutions wherever power needs to be combined with reliability.  The requirement for secure power sources is growing in many applications. Thermal battery technology provides unexploited benefits for innovative applications.