Thermal batteries are designed to activate at high temperatures (~500℃), therefore, the electrodes used in these systems are typically made into pellet form using compression molding techniques that do not involve polymer binders. However, the compression molding technique poses limitations in scaling up the electrode area without increasing thickness for high-power properties. Additionally, the tape casting method has been studied as a way to solve with, but too low a loading level is still an obstacle to practical use. This study fabricated a film cathode of high loading level (35.79 mAh·cm-2) using the tape casting method for these problem. As utilized fabricated cathode, it investigated the influence of electrode thickness and density on electrochemical performance. Furthermore, a film cathode with a larger area but the same amount of active material as the pellet was fabricated, enabling the design of high-power cells with the same energy density. We expect that the fabricated film cathode with a high loading level and scalable area will enable the development of various thermal battery designs.
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Manufacturing Process Optimization of Oxide-Based Multilayer Ceramic Batteries Using Multilayer Ceramic Processing Technologies Won-Su Lee, Jong Kyu Lee, Jung Rag Yoon Journal of Electrical and Electronic Materials.2026; 39(5): 519. CrossRef
Thermal batteries are used in military power sources that require robustness and long storage life for applications in missiles and torpedoes. FeS2 powder is currently used as a cathode material because of its high specific energy density, environmental non-toxicity, and low cost. MS2 (M = Fe, Ni, Co) cathodes have been explored as novel candidates for thermal batteries in many studies; however, the discharge characteristics (1, 2, 3 plateau) of single cells in thermal batteries with different cathodes have not been elucidated in detail. In this study, we independently analyzed the discharge voltage and calculated the total polarizations of single cells using MS2 cathodes. Based on the results of this study, we propose NiS2 as a potential cathode material for use in thermal batteries.
For comparison to the Li-ion battery, evaluating a thermal battery must consider additional variables. The first one is the temperature difference between the battery and its unit cell. Thermal batteries and their unit cells have a temperature difference that is caused by the thermal battery activation mechanism and its shape. The second variable is the electrochemical reaction steps. Most Li-ion batteries have a constant electrochemical reaction at the electrode, and battery voltage is affected when the concentration of Li ions is changed. However, a thermal battery has several steps in its electrochemical reaction, and each step has a different potential. In this study, we used unit cell discharge tests based on interpolating a 4D lookup table to estimate the performance of a thermal battery. From the test results, we derived an estimation algorithm by interpolating the table, which is queried from specified profile groups. As a result, we found less than a 5 percent difference between estimation and experiment at the 1.3 V cut-off time.
Powder compaction technology is widely used to prepare thermal battery components. This method, however, is limited by the size, thickness, and geometry of the battery components. This limitation leads to excessive cell capacity, overweight, and higher cost of the pellets, which decreases the specific capacities and delays the activation time of thermal batteries. FeS2 thin-film cathodes were fabricated by tape-casting technology and analyzed by SEM and EDS in this paper. The residual organic binder of the FeS2 thin-film cathodes decreased with the temperature of the heat treatment, which improved the specific capacity because of the lower resistance. Specific capacities of the FeS2 thin-film cathodes decreased because of the higher residual binder and the restrictive reaction of active materials with molten salts as the thickness increased. FeS2 thin-film cathodes showed much higher specific capacity (1,212.2 As/g) than pellet cathodes (860.7 As/g) at the optimal heat-treatment temperature (230℃).
Pulverized FeS2 (pyrite) gives different discharge test results with as-received FeS2 electrodes. The as-received FeS2 electrode shows three voltage plateaus during the discharge test. However, the ball-milled FeS2 electrode shows two voltage plateaus. To interpret this result, the effect of FeS2 particle size on electrochemical reactions is investigated by unit cell discharge tests, SEM and XRD. As a result, it is found that the transition reaction product (Li2 + xFe + xS2) of FeS2 explains the difference. The as-received FeS2 reacts according to three reaction steps (FeS2 → Li3Fe2S4 → Li2 + xFe1 + xS2 → LiFe2S4). However, ball-milled FeS2 reacts without the Li2 + xFe1 + xS2 stage. In this study, this result is explained by the difference in electrochemical reaction mechanism. The as-received FeS2 has a larger radius than the ball-milled FeS2. Therefore, the lithium ion has to diffuse into the FeS2 unreacted core, and Li2 + xFe1 + xS2, the transition reaction product of as-received FeS2, is formed during this stage.
Thermal batteries use inorganic salt as electrolyte, which is inactive at room temperature. As soon as heat pellets are fired by an igniter, all the solid electrolytes are instantly melted into excellent ionic conductors. However, the abnormal heat generation by the igniter flame or heat pellets causes the thermal decomposition of the electrode and the melting of the anode, eventually leading to a thermal runaway, which results in overheating or explosion. The thermal runaway can be significantly reduced by the adoption of Zr/BaCrO4 heat papers. In this study, the heat papers with various ratios of fuel (Zr) and oxidizer (BaCrO4) were prepared by the paper-making process. We have investigated the calorimetric value, burning rate, and ignition sensitivity. The ignition test of heat pellets and the discharge test of thermal batteries were also carried out. At the composition of 40 wt.% of Zr, the heat papers showed the highest specific calorimetric value and burning rate. As a result, Zr/BaCrO4 heat paper made by the paper-making process has shown the applicability for thermal batteries.
Thermal batteries are heat-activated primary reserve power sources that use inorganic salt as electrolytes and specially designed to meet extremely long or environmentally severe storage requirements. They are primarily used to deliver high power for relatively short periods in such applications as fuzes, missiles, ordnance and other military applications. In this paper, we describe a general overview and research trends on electrode materials for thermal batteries.
Thermal batteries are primary power sources for military applications requiring high reliability, robustness and long storage life. Conventional electrodes for thermal batteries are prepared by compacting powder mixtures into pellets. Separator is composed of halide mixture, such as LiCl-KC1 eutectic salt, blended with MgO to immobilize the molten salt. In order to increase the power density and energy density, the resistance of electrolyte should be reduced because the resistance of electrolyte is predominant in thermal batteries. In this study, wetting behaviors and impregnation weight of molten salts as well as the micro structures of ceramic felt were investigated to be applicable to thin electrolyte. Discharge performances of single cell with the ceramic separator impregnated by molten salt were evaluated also. Zirconia felt with high porosity and large pore outperformed alumina felt in wetting characteristics and molten salt impregnation as well as discharge performances. Based on the results of this study, ceramic felt separator impregnated with molten salt have revealed as an alternative of conventional thick MgO based separator with no conspicuous sign of thermal runaway by short circuit.
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RETRACTED: Optimization of thermal battery electrolytes: Ionic diffusion, conductivity enhancement, and structural effects in lithium salt systems for military-grade thermal batteries Lifeng Zheng, Xing Li Case Studies in Thermal Engineering.2026; 83: 108191. CrossRef
Thermal batteries are primary reserve batteries that use inorganic salt as electrolytes which areinactive at room temperature. The two principal heat sources that have been used in thermal batteries areheat paper and heat pellets. As soon as the heat paper, which is ignited by the initiator, in turn ignites theheat pellets, all the solid electrolytes are melted into excellent ionic conductors. However, the highcombustion temperature by heat papers in thermal batteries causes thermal decomposition at the cathode,eventually leading to a thermal runaway. In this paper, we have attempted to prepare Zr/BaCrO4 heatpapers coated with KCl molten salt. We have also investigated the effect of a molten salt coating on theheat papers through the thermal characteristics such as calorimetric value, combustion temperature andburning rate. The calorimetric value and combustion temperature of heat papers were reduced with anincrease in the molten salt coating. As a result, the molten salt coating on heat papers greatly reducedrisk of a thermal runaway and improved the stability of thermal batteries.
Thermal batteries are used for military power sources that require robustness and long storagelife such as missiles and torpedoes. FeS2 powder is currently used for cathode materials because of itshigh specific energy density, environmental non-toxicity and low cost. However, large particle size ofconventional FeS2 has been deterred its possible application for higher power thermal batteries. In order toimprove the power density, high energy ball milling of FeS2 has been introduced to crush the micron-sizedFeS2. Discharge characteristics of the single cells fabricated with nano-materials and conventional FeS2powder were evaluated.
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