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This paper proposes low-melting-point eutectic salts containing RbCl as electrolytes for light weight thermal batteries. The handleability of the eutectic salts was remarkably improved for commercialisation. Their performance as thermal battery molten-salt electrolytes was verified using tests on a single cell and a 12-cell stacked battery.

High-energy-density rechargeable batteries have been gaining considerable importance in the field of renewable energy, and Li-infused anodes are potential candidates for the development of such batteries. However, the poor cycling and dimensional stability of Li affects their performance. As most materials used in battery manufacturing are lithiophobic to molten Li, infusion of Li into the porous structures with an intrinsically lithiophobic surface presents challenges in the development of Li batteries. Optimising and improving the wettability of molten Li is one approach to address this. Herein, we propose a very practical and straightforward oxidation method for achieving an ultra-lithiophilic NiO layer on the surface of a three-dimensional Ni-foam. Oxidation of the Ni-foam in air resulted in a remarkable increase in the wettability of molten Li on the Ni surface, with a decrease in the wetting angle from 120° to 0°. A NiO layer was epitaxially grown on the surface of the Ni-foam, with a thickness of several hundreds of nanometres. This layer was lithiophilic and showed high electrical conductivity. An anode prepared using Li-infused oxidised Ni-foam showed no evidence of short circuits or dendrite formation after 1000 cycles of stripping and plating at 0.1 and 0.5 mA cm−2, whereas a pure Li anode showed unstable stripping and plating behaviour at 0.5 mA cm−2. The proposed surface-treatment method is considered the most simple and practical method among those reported to date, and the Ni-foam produced using this method showed excellent anode performance. Hence, the proposed method will facilitate further development of rechargeable lithium-metal battery technology.

Although numerous cathode materials with excellent properties have been developed for use in molten salt thermal batteries, similar progress is yet to be made with anode materials. Herein, a high-performance lithium-impregnated metal foam anode (LIMFA) is fabricated by impregnating molten lithium into a gold-coated iron–chrome–aluminum (FeCrAl) foam at 400°C. A test cell employing the LIMFA FeCrAl anode exhibited a specific capacity of 2,627 As·g−1. For comparison, a cell with a conventional Li(Si) anode was also discharged, demonstrating a specific capacity of 982 As·g−1. This significant improvement in performance can be attributed to the large amount (18 wt.%) of lithium incorporated into the FeCrAl foam and the ability of the FeCrAl foam to absorb and immobilize molten lithium without adopting a cup system. For thermal batteries without a cup, the LIMFA FeCrAl provides the highest-reported specific capacity and a flat discharge voltage curve of molten lithium. After cell discharge, the FeCrAl foam exhibited no lithium leakage, surface damage, or structural collapse. Given these advantageous properties, in addition to its high specific capacity, LIMFA FeCrAl is expected to aid the development of thermal batteries with enhanced performance.

In this study, effects of pyrite () particle sizes on the electrochemical characteristics of thermal batteries are investigated using unit cells made of pulverized pyrite by ball-milling. At unit cell discharge test, the electrochemical capacity of pyrite-cell largely increases compared to pyrite-cell, and their internal resistances also decrease. These results are attributed to the increase in the active reaction area of pyrite by ball milling. However, at unit cell discharge test, a pyrite cell shows lower internal resistance than that of pyrite cell only at Z-phase region (). After that, a pyrite cell shows a decrease in the cell voltage and an rapid increase of the internal resistance in J-phase region () is observed compared to those of pyrite cell. It can be concluded that at the higher temperature, the thermally unstable pulverized pyrite is decomposed thermally as well as self discharged, simultaneously, which causes the higher resistance and lower capacity at in J-phase than that of pyrite cell.

Microstructure and thermal stability of mechanically ball milled were investigated. The average particle size and distribution of powder were changed in two steps with the increased ball milling time. The average particle size drastically decreased from to 1.01 and after ball milling of 10 h and 30 h, respectively. However, the distribution was broad and a shoulder appeared at because the pulverization was still in process at 10 h ball milling. After 60 h ball milling, the distribution became narrower. After ball milling of 120 h, the average particle size increased because of particle agglomeration. Therefore, the particle size distribution became broaden again. Finally, after ball milling of 170 h, with the narrowest size distribution can be obtained. Thermal stability of was unstable as the particle was pulverized. Therefore, the activation energy of the fine size particles is 27% lower than that of the as-received .

Lithium-impregnated metal foam anodes (LIMFAs) are fabricated and investigated. The LIMFAs are prepared by the impregnation of lithium into molten-salt-coated nickel metal foam. A single cell with the LIMFA exhibits a specific capacity of 3009 As g−1. For comparison, a single cell with a LiSi alloy anode is also discharged, demonstrating a specific capacity of 1050 As g−1. These significant improvements can be attributed to the large amount of lithium impregnated into the metal foam as well as the molten lithium holding capability of the foam. Due to their excellent electrochemical properties, LIMFAs are suitable for use in thermal batteries.

4 Agency for defense development, chochiwongil 462, Yuseong-Ku, Daejeon 305-152, Korea Abstract >> A proper stacking force and assembly are important to the performance of fuel cell. Improper assembly pressure may lead to leakage of fuels and high interfacial contact resistance, excessive assembly pressure may result in damage to the gas diffusion layer and other components. The pressure distribution of gas diffusion layer is important to make interfacial contact resistance less for stack performance. To analyze the influence of design parameter factors for pressure distribution, and to optimize stack design, DOE (Design of Experiment) was used for polymer electrolyte membrane fuel cell stack pressure test. As commonly known, the higher clamping force improves the fuel cell stack performance. However, non-uniformity of stress distribution is also increased. It shows that optimization between clamping force and stress distribution is needed for well designed structure of fuel cell stack. In this study, stack design optimization method is suggested by using FEM (Finite Element Methode) and DOE for light-weighted fuel cell stack.

3 Agency for defense development, chochiwongil 462, Yuseong-Ku, Daejeon 305-152, Korea Abstract >> In this paper, the development and performance analysis of a fuel cell-powered unmanned aerial vehicle is described. A fuel cell system featuring 1 kW proton exchange membrane fuel cell combined with a highly pressurized fuel supply system is proposed. For the higher fuel consumption efficiency and simplification of overall system, dead-end type operation is chosen and each individual system such as purge system, fuel supply system, cooling system is developed. Considering that fluctuation of exterior load makes it hard to stabilize fuel cell performance, the power management system is designed using a fuel cell and lithium-ion battery hybrid system. After integration of individual system, the performance of unmanned aerial vehicle is analyzed using data from flight and laboratory test. In the result, overall system was properly operated but for more duration of flight, research on weight lighting and improvement of fuel efficiency is needed to be progressed.

Thermal batteries have excellent mechanical robustness, reliability, and long shelf life. Due to these characteristics as well as their unique activation mechanism, thermal batteries are widely adopted as military power sources. Li(Si)/ thermal batteries, which are used mostly in these days, use LiCl-KCl and LiBr-LiCl-LiF as molten salt electrolyte. However, it is known that Li(Si)/ thermal batteries have high internal resistance. Especially, cathode accounts for the greater part of internal resistance in unit cell. Many efforts have been put into to decrease the internal resistance of thermal batteries, which result in the development of new electrode material and new electrode manufacturing processes. But the applications of these new materials and processes are in some cases very expensive and need complicated additional processes. In this study, internal resistance study was conducted by adding carbon black and carbon nano-tube, which has high electron conductivity, into the cathode. As a results, it was found that the decrease of internal resistance of cathode by the addition of carbon black and carbon nano-tube.