A eutectic salt for thermal batteries

Abstract

This invention relates to a eutectic salt for thermal batteries, belonging to the field of electrochemical technology. The eutectic salt for thermal batteries of this invention comprises LiCl, LiBr, LiF, and BaCl2, with the following mass percentage contents: LiCl 11%–20%, LiBr 50%–70%, LiF 6%–12%, and BaCl2 16%–30%. This invention uses a LiCl-LiBr-LiF-BaCl2 eutectic salt with a melting point of 421.6℃. This is approximately 18.2℃ lower than the commonly used LiCl-LiBr-LiF eutectic salt (melting point 439.8℃). This invention has the following significant advantages: First, using the eutectic salt of this invention as an electrolyte in thermal batteries can extend the operating temperature range of the thermal battery, thus extending its thermal life and operational life. Second, the lower melting point reduces the amount of heating agent required, while simultaneously improving the specific energy and safety of the thermal battery. Third, this eutectic salt retains the high conductivity advantage of the LiCl-LiBr-LiF eutectic salt.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a low-eutectic salt for thermal batteries. Background Technology

[0002] A thermal battery is a high-temperature storage primary battery. At room temperature, the electrolyte is solid and non-conductive. During use, a heating element is ignited through electrical or mechanical activation. Under the action of a heating agent, the internal temperature of the battery rises rapidly, causing the electrolyte to melt and form a highly conductive ionic conductor. This initiates the thermal battery's operation, allowing it to output electrical energy to the power system within a short time. Thermal batteries offer advantages such as short activation time, high output power, wide operating temperature range (-50℃ to 70℃), long storage time, strong resistance to mechanical environments, and high reliability. Currently, thermal batteries are widely used in advanced weaponry, such as missiles, nuclear weapons, various advanced bombs, artillery shells, mines, and ignition devices of some combat weapons.

[0003] Once activated, the battery remains operational as long as the eutectic salt remains molten, until all the active materials involved in the reaction are exhausted. However, due to heat loss, the battery will prematurely stop operating once the temperature drops below the electrolyte's eutectic point, causing the eutectic salt to re-solidify.

[0004] When the amount of electroactive material is certain and sufficient, the thermal life determines the working life of the thermal battery. A longer thermal life can be achieved by adjusting the thermal design, but higher heat levels reduce the safety and reliability of the thermal battery.

[0005] Common methods for extending the thermal life of thermal batteries include:

[0006] 1) Enhance the insulation effect by using high-performance insulation materials or thickening the insulation layer. However, high-performance insulation materials are expensive and thickening the insulation layer takes up a lot of space.

[0007] 2) Increase the heat capacity of the thermal battery stack, for example, by adding heat storage plates at appropriate locations in the battery structure. However, adding heat storage plates will reduce the specific energy and specific power of the thermal battery.

[0008] 3) Use low-melting-point eutectic salts to reduce the internal and external temperature difference during thermal battery operation.

[0009] 4) Within the operating temperature range of the thermal battery, the internal operating temperature of the thermal battery is designed to be in the high-temperature range, and the time for the internal temperature of the thermal battery to drop to the solidification of the eutectic salt is extended by increasing the internal heat capacity.

[0010] 5) Using low-melting-point eutectic salts widens the operating temperature range of the thermal battery without causing other significant adverse effects on the thermal battery.

[0011] Commonly used eutectic salts for thermal batteries include LiCl-KCl, LiF-LiCl-LiBr, LiF-KCl-LiBr, and LiF-KBr-LiBr. Among them, LiF-LiCl-LiBr is often used in thermal batteries that require high current density output due to its high conductivity, but its melting point is 449℃ and its operating temperature is relatively high.

[0012] Currently, the ternary eutectic salt LiF-LiCl-LiBr, which is commonly used in thermal batteries, is widely applied due to its good electrical conductivity. Summary of the Invention

[0013] (a) Technical problems to be solved

[0014] The technical problem to be solved by the present invention is how to provide a low eutectic salt for thermal batteries, in order to solve the problem of how to retain the high conductivity of the low eutectic salt and reduce the melting point of the low eutectic salt.

[0015] (II) Technical Solution

[0016] To solve the above-mentioned technical problems, the present invention proposes a eutectic salt for thermal batteries, which comprises LiCl, LiBr, LiF and BaCl2, with the following mass percentage contents: LiCl 11% to 20%, LiBr 50% to 70%, LiF 6% to 12%, and BaCl2 16% to 30%.

[0017] The present invention also provides a method for preparing an electrolyte for a thermal battery, the method comprising the following steps:

[0018] S1. Pretreatment: The LiCl, LiBrg, LiF, BaCl2, and MgO are dried in a vacuum oven and then ball-milled and sieved.

[0019] S2. Preparation of electrolyte: Using an electronic scale with an accuracy of 0.1g, weigh LiCl, LiBr, LiF and BaCl2 according to the following mass percentages: LiCl 11%~20%, LiBr 50%~70%, LiF 6%~12%, BaCl2 16%~30%. First, put LiCl, LiBr, LiF and BaCl2 into a crucible and melt them. After melting, stir in the crucible with a quartz rod and quickly pour the melt into a stainless steel pan, spread it into a thin sheet and crush it. Crush it with a pulverizer to obtain the eutectic salt LiCl-LiBr-LiF-BaCl2 powder.

[0020] S3. Then, MgO is added to the eutectic salt LiCl-LiBr-LiF-BaCl2 powder and mixed evenly to melt it. The melt is then quickly poured into a stainless steel pan, spread into thin sheets, and crushed. After being crushed with a pulverizer, the electrolyte LiCl-LiBr-LiF-BaCl2-MgO is obtained.

[0021] (III) Beneficial Effects

[0022] This invention proposes a low-melting-point eutectic salt for thermal batteries. The proposed salt is a LiCl-LiBr-LiF-BaCl2 low-melting-point eutectic salt with a melting point of 421.6℃. This is approximately 18.2℃ lower than the commonly used LiCl-LiBr-LiF low-melting-point eutectic salt (melting point 439.8℃). This invention offers the following significant advantages: First, using this low-melting-point eutectic salt as an electrolyte in thermal batteries can extend the operating temperature range, thermal life, and operational life of the batteries. Second, the lower melting point reduces the amount of heating agent required, while simultaneously improving the specific energy and safety of the thermal batteries. Third, this low-melting-point eutectic salt retains the high conductivity advantage of the LiCl-LiBr-LiF low-melting-point eutectic salt.

[0023] Practical application: The novel eutectic salt LiCl-LiBr-LiF-BaCl2 of this invention was used in a certain type of thermal battery, and the working time of the thermal battery was 36 seconds. Attached Figure Description

[0024] Figure 1 Thermal analysis curves of eutectic salts for thermal batteries and LiCl-LiBr-LiF eutectic salts. Detailed Implementation

[0025] To make the objectives, contents, and advantages of the present invention clearer, the specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples.

[0026] This invention provides a novel low-melting-point eutectic salt for thermal batteries. Using this electrolyte in thermal batteries can effectively extend the thermal life and operational life of the batteries while reducing the amount of heating agent required. This eutectic salt retains the high conductivity advantage of LiCl-LiBr-LiF eutectic salts.

[0027] The thermal battery eutectic salt included in this invention adopts the following technical solution:

[0028] The first technical problem to be solved by the present invention is to retain the high electrical conductivity of the eutectic salt, thereby retaining its good electrical conductivity, and retaining the three components of LiCl, LiBr and LiF in the main components.

[0029] The second technical problem to be solved by the present invention is to lower the melting point of eutectic salts by adding new inorganic salts to form quaternary eutectic salts.

[0030] The novel eutectic salt for thermal batteries described in this invention comprises LiCl, LiBr, LiF, and BaCl2, with the following mass percentage contents: LiCl 11%–20%, LiBr 50%–70%, LiF 6%–12%, and BaCl2 16%–30%.

[0031] Example 1:

[0032] The present invention will be further illustrated below with reference to specific embodiments. These embodiments should be understood as being used only to illustrate the present invention and not as limiting the scope of protection of the present invention.

[0033] The method for preparing the electrolyte for a thermal battery according to the present invention includes the following steps:

[0034] S1. Pretreatment: Drying is carried out in a vacuum oven at a temperature of 150℃~200℃; the dried LiCl, LiBrg, LiF, BaCl2, and MgO are then ball-milled and sieved.

[0035] S2. Preparation of the electrolyte: Using an electronic scale with an accuracy of 0.1g, weigh out the following mass percentages: LiCl 11%–20%, LiBr 50%–70%, LiF 6%–12%, and BaCl2 16%–30%. First, place LiCl, LiBr, LiF, and BaCl2 into a crucible and melt them in a box-type resistance furnace at 550℃ for 90 minutes. After melting, stir the mixture in the crucible with a quartz rod, and quickly pour the melt into a stainless steel pan, spread it into thin sheets, and crush it. Then, pulverize the powder using a pulverizer to obtain the aforementioned eutectic salt LiCl-LiBr-LiF-BaCl2 powder.

[0036] S3. Then, add MgO to the eutectic salt LiCl-LiBr-LiF-BaCl2 powder and mix evenly. Melt in a box-type resistance furnace at 550℃ for 90 minutes, and then quickly pour the melt into a stainless steel pan, spread it into a thin sheet and crush it. After crushing with a pulverizer, the electrolyte LiCl-LiBr-LiF-BaCl2-MgO is obtained.

[0037] Test method: The melting point of the eutectic salt LiCl-LiBr-LiF-BaCl2 was tested using a Netzsch STA409PC differential scanning calorimeter (DSC). The heating and cooling rates were both 20℃ / min, under nitrogen protection, and the DSC curves were recorded. The results are shown in the attached figure. The melting point of the eutectic salt used in this thermal battery is 421.6℃.

[0038] Practical application: The electrolyte LiCl-LiBr-LiF-BaCl2, prepared by the low eutectic salt of the thermal battery of the present invention, is used in a certain type of thermal battery. The working time of the thermal battery is 36s.

[0039] Comparative Example

[0040] Electrolyte preparation: Using an electronic scale with an accuracy of 0.1g, weigh 22.0g of pretreated LiCl, 68.44g of LiBr, and 9.56g of LiF and place them in a crucible. Melt in a box-type resistance furnace at 500℃ for 45min. After melting, stir in the crucible with a quartz rod and quickly pour the melt into a stainless steel pan, spread it into thin sheets, crush it, and pulverize it with a pulverizer to obtain the eutectic salt LiCl-LiBr-LiF powder. Weigh 50g of the eutectic salt LiCl-LiBr-LiF powder and 50g of active magnesium oxide, mix them evenly, and pour them into a crucible. Melt in a box-type resistance furnace at 550℃ for 60min. Spread the mixture into sheets, pulverize it, and sieve it to obtain the electrolyte LiCl-LiBr-LiF-MgO.

[0041] Test method: The melting point of the eutectic salt LiCl-LiBr-LiF-MgO was determined using a Netzsch STA409PC differential scanning calorimeter (DSC). The heating and cooling rates were both 20℃ / min, under nitrogen protection, and the DSC curves were recorded. The test results showed... Figure 1 The results show that the melting point of the eutectic salt LiCl-LiBr-LiF is 439.8℃.

[0042] Practical application: The electrolyte LiCl-LiBr-LiF-MgO, prepared from the LiCl-LiBr-LiF eutectic salt, was used in the same type of thermal battery as in the example, with an appropriate reduction in the amount of heating agent. All other conditions were the same as in the example, and the working time of the thermal battery was 25 seconds.

[0043] The results above show that the eutectic salt LiCl-LiBr-LiF-BaCl2 used in this invention for thermal batteries has a melting point of 421.6℃. This is approximately 18.2℃ lower than the commonly used LiCl-LiBr-LiF eutectic salt (439.8℃). Using the electrolyte of this invention in thermal batteries can effectively extend the thermal life and working life of the batteries, reduce the amount of heating agent used, and simultaneously improve the specific energy and application safety performance of the thermal batteries.

[0044] This invention utilizes a LiCl-LiBr-LiF-BaCl2 eutectic salt with a melting point of 421.6℃. This is approximately 18.2℃ lower than the commonly used LiCl-LiBr-LiF eutectic salt (melting point 439.8℃). This invention offers the following significant advantages: First, using this eutectic salt as an electrolyte in thermal batteries can extend the operating temperature range, thermal life, and operational life of the batteries. Second, the lower melting point reduces the amount of heating agent required, while simultaneously improving the specific energy and safety of the thermal batteries. Third, this eutectic salt retains the high conductivity of the LiCl-LiBr-LiF eutectic salt.

[0045] Practical application: The novel eutectic salt LiCl-LiBr-LiF-BaCl2 of this invention was used in a certain type of thermal battery, and the working time of the thermal battery was 36 seconds.

[0046] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A eutectic salt for thermal batteries, characterized in that, The eutectic salt comprises LiCl, LiBr, LiF, and BaCl2, with the following mass percentage contents: LiCl 11%–20%, LiBr 50%–70%, LiF 6%–12%, and BaCl2 16%–30%.

2. A method for preparing an electrolyte for a thermal battery, characterized in that, The method includes the following steps: S1. Pretreatment: The LiCl, LiBrg, LiF, BaCl2, and MgO are dried in a vacuum oven and then ball-milled and sieved. S2. Preparation of electrolyte: Using an electronic scale with an accuracy of 0.1g, weigh LiCl, LiBr, LiF and BaCl2 according to the following mass percentages: LiCl 11%~20%, LiBr 50%~70%, LiF 6%~12%, BaCl2 16%~30%. First, put LiCl, LiBr, LiF and BaCl2 into a crucible and melt them. After melting, stir in the crucible with a quartz rod and quickly pour the melt into a stainless steel pan, spread it into a thin sheet and crush it. Crush it with a pulverizer to obtain the eutectic salt LiCl-LiBr-LiF-BaCl2 powder. S3. Then, MgO is added to the eutectic salt LiCl-LiBr-LiF-BaCl2 powder and mixed evenly to melt it. The melt is then quickly poured into a stainless steel pan, spread into thin sheets, and crushed. After being crushed with a pulverizer, the electrolyte LiCl-LiBr-LiF-BaCl2-MgO is obtained.

3. The method for preparing the electrolyte for a thermal battery as described in claim 2, characterized in that, In step S1, the drying temperature is 150℃~200℃.

4. The method for preparing the electrolyte for a thermal battery as described in claim 2, characterized in that, In step S2, the material is melted in a box-type resistance furnace at 550°C.

5. The method for preparing the electrolyte for a thermal battery as described in claim 4, characterized in that, In S2, the melting time is 90 minutes.

6. The method for preparing the electrolyte for a thermal battery as described in claim 2, characterized in that, In step S3, the material is melted in a box-type resistance furnace at 550°C.

7. The method for preparing the electrolyte for a thermal battery as described in claim 6, characterized in that, In S3, the melting time is 90 minutes.

8. The method for preparing an electrolyte for a thermal battery according to any one of claims 2-7, characterized in that, The method also includes: using differential scanning calorimetry (DSC) to test the melting point of the eutectic salt LiCl-LiBr-LiF-BaCl2, with both heating and cooling rates at 20℃ / min, under nitrogen protection, and recording the DSC curves.

9. The method for preparing the electrolyte for a thermal battery as described in claim 8, characterized in that, The differential scanning calorimeter used is STA409PC.

10. The method for preparing the electrolyte for a thermal battery as described in claim 8, characterized in that, The eutectic salt LiCl-LiBr-LiF-BaCl2 was formulated into an electrolyte, LiCl-LiBr-LiF-BaCl2-MgO, which was then used in a certain type of thermal battery.

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