Molten salt electrolyte material, preparation method thereof and fluorine ion thermal battery prepared from molten salt electrolyte material

Abstract

The invention discloses a molten salt electrolyte material, a preparation method thereof and a prepared fluorine ion thermal battery, a porous silicon dioxide material adsorbs molten eutectic salt at high temperature to prepare the molten salt electrolyte material, and the molten salt electrolyte material is applied to the fluorine ion thermal battery. In the obtained electrolyte material, silicon dioxide is used as a molten salt adsorbent and a flow inhibitor, and a larger specific surface area can adsorb a higher proportion of molten eutectic salt, so that the rapid conduction capability of fluorine ions in the electrolyte is enhanced. The silicon dioxide and the fluorine ion thermal battery positive and negative electrode material are inert in high-temperature reaction, so that side reaction in the discharge process is avoided, and the utilization efficiency of the fluorine ion thermal battery positive and negative electrodes is improved. In addition, the silicon dioxide with relatively strong adsorption capacity can block the dissolving shuttling of positive and negative electrode materials, so that the high-temperature no-load safety is improved, and the discharge performance of the fluorine ion thermal battery is further improved.

Description

Technical Field

[0001] This invention belongs to the field of fluorine-ion thermal battery technology, specifically relating to a molten salt electrolyte material, its preparation method, and the fluorine-ion thermal battery prepared therefrom. Background Technology

[0002] A thermal battery is an energy storage device that achieves a single high-energy-density discharge through an irreversible redox reaction by melting and activating an inorganic eutectic salt electrolyte under external thermal triggering. It possesses core advantages such as high specific power, rapid activation speed, and good environmental adaptability, making it an irreplaceable special power source in high-power military scenarios such as aerospace, missiles, and torpedoes. However, with the increasing demands of modern weapon systems for instantaneous energy density, discharge life, and reliability in extreme environments, traditional thermal battery systems are gradually facing performance bottlenecks. Therefore, developing high-specific-energy thermal battery systems based on novel electrode materials to break through existing technological limitations has become an urgent need in the defense science and technology field.

[0003] Fluorine-ion batteries, as a novel energy storage system, use metal fluorides as the positive electrode material. Their negative electrode materials (alkaline earth or rare earth metals and their fluorides) possess high melting points and thermal stability, fundamentally avoiding the liquid metal leakage risks associated with lithium-ion batteries. Fluorine-ion batteries convert chemical energy into electrical energy through the migration of fluorine ions as charge carriers. Their unique working mechanism demonstrates groundbreaking potential. Benefiting from the low atomic mass of fluorine, the high voltage of the metal fluoride positive electrode material, and the high specific capacity due to the participation of multiple electrons in redox reactions, the theoretical energy density of fluorine-ion batteries reaches as high as 5000 Wh / L. -1 Therefore, fluoride-ion thermal batteries have inherent advantages in both energy density and safety, providing a revolutionary solution for thermal batteries. In the electrolyte membrane of fluoride-ion thermal batteries, porous magnesium oxide is typically used as an adsorption carrier and flow inhibitor for molten eutectic salts, adsorbing the high-temperature molten eutectic salts and preventing short circuits caused by their flow. However, magnesium oxide has a low specific surface area, resulting in a low content of molten salt for conducting fluoride ions in the electrolyte membrane, leading to poor ionic conductivity. Furthermore, magnesium oxide has poor high-temperature chemical stability with commonly used negative electrode metals (such as Al) in fluoride-ion thermal batteries, causing compatibility issues at the negative electrode / electrolyte interface. This hinders the fluorination reaction at the negative electrode, severely impacting the discharge capacity and energy density of the fluoride-ion thermal battery.

[0004] For example, CN202010207655.1 describes a novel fluorine-ion thermal battery and its preparation method. This fluorine-ion thermal battery does not lose capacity at high temperatures, can improve the specific energy of the thermal battery, and reduce the battery's height. CN202411652924.X describes an alloy anode material and its preparation method, and the prepared fluorine-ion thermal battery, which can improve the utilization rate of the metal anode and enhance discharge performance. However, while the above-mentioned novel fluorine-ion thermal battery preparation methods and rationalized alloy anode material preparation methods can improve the discharge specific energy when applied to fluorine-ion thermal batteries, the electrolyte materials used all employ magnesium oxide as a molten salt adsorbent and flow inhibitor. This not only leads to side reactions between magnesium oxide and electrode materials at high temperatures, affecting the specific energy of the fluorine-ion thermal battery, but also the excessive use of inert magnesium oxide adsorbent can affect the ionic conductivity of the molten salt electrolyte, resulting in excessive discharge internal resistance of the fluorine-ion thermal battery. Furthermore, the limited adsorption capacity of magnesium oxide cannot effectively suppress the dissolution and shuttle of electrode materials in the molten eutectic salt at high temperatures, which can easily cause safety hazards in the thermal battery. Summary of the Invention

[0005] To address the technical challenges of poor ionic conductivity and poor high-temperature chemical stability of magnesium oxide-containing electrolyte membranes in fluoride-ion thermal batteries, this invention provides a molten salt electrolyte material, its preparation method, and the resulting fluoride-ion thermal battery.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a molten salt electrolyte material, comprising, by mass percentage, 10%-60% adsorbent carrier and 40%-90% molten eutectic salt.

[0007] The adsorption carrier is a porous silica material.

[0008] The molten eutectic salt is one of LiF-BeF2, NaF-BeF2, LiF-NaF-BeF2, LiF-ZrF4, NaF-ZrF4, KF-ZrF4, RbF-ZrF4, LiF-NaF-ZrF4, LiF-NaF-KF, NaF-KF-CsF, LiF-NaF-KF-CsF, and LiF-NaF-RbF.

[0009] The preparation method of the above-mentioned molten salt electrolyte material includes the following steps: (1) Place the porous silica material in a high-temperature furnace, heat and keep it warm to remove high-temperature unstable impurities; (2) Weigh the cooled silica and eutectic salt according to the target stoichiometric ratio and mix them evenly; (3) Place the mixed materials in a high-temperature furnace, heat and keep warm under a special atmosphere; (4) After the heat preservation is completed, take out the molten salt electrolyte material and pour it into a cooling pan to cool to room temperature; (5) The cooled molten salt electrolyte is crushed and sieved to obtain molten salt electrolyte powder.

[0010] The porous silica material has an average pore size of 20-50 nm and a specific surface area of ​​100-200 m². 2 / g.

[0011] The purity of the silicon dioxide material is ≥99%.

[0012] The purity of the eutectic salt raw materials is ≥99%.

[0013] The silicon dioxide firing temperature is 300~800℃.

[0014] The silicon dioxide firing and holding time is 1 to 6 hours.

[0015] The special atmosphere is either argon or nitrogen, with a purity of 99.99% or higher.

[0016] The molten salt electrolyte is heated at a temperature of 320~600℃.

[0017] The molten salt electrolyte is heated and kept at a constant temperature for 1 to 3 hours.

[0018] A fluorine-ion thermal battery, wherein the electrolyte material is the molten salt electrolyte material described above or the molten salt electrolyte material prepared by the above preparation method.

[0019] The beneficial effects of this invention are as follows: The molten salt electrolyte for fluoride-ion batteries prepared using porous silica as a molten salt adsorbent and flow inhibitor is convenient to prepare, uses readily available and simple raw materials, and has a reasonable composition design. Silica material exhibits good high-temperature chemical stability compared to commonly used electrode materials in fluoride-ion thermal batteries, which is beneficial for improving the effective utilization rate of the positive and negative electrode active materials in fluoride-ion thermal batteries. Porous silica material has a high specific surface area, allowing it to adsorb more molten eutectic salt at a lower content, resulting in higher ionic conductivity of the molten salt electrolyte and reducing the discharge internal resistance of the fluoride-ion thermal battery. The strong adsorption performance of silica adsorbent can effectively block the dissolution and shuttle of positive and negative electrode materials at high temperatures, improving the high-temperature no-load safety of fluoride-ion thermal batteries. Attached Figure Description

[0020] Figure 1 This is a SEM image of the molten salt electrolyte powder material prepared in Example 1 of the present invention.

[0021] Figure 2 This is a nitrogen adsorption-desorption curve of the porous silica material prepared in Example 2 of the present invention.

[0022] Figure 3EIS images of the molten salt electrolyte electrodes prepared in Example 1 and Comparative Example 1 of this invention.

[0023] Figure 4 The high-temperature no-load curves are for the fluorine-ion thermal batteries assembled in Application Example 1 and Comparative Example 1 of this invention. Detailed Implementation

[0024] The present invention will be further illustrated below with reference to specific embodiments. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. Furthermore, it should be understood that after reading the disclosure of this invention, those skilled in the art can make various modifications or alterations to the present invention, and these equivalent forms also fall within the protection scope defined by this invention.

[0025] Example 1 Weigh 50g of porous silica material with a purity of 99% and place it in a crucible; place the crucible in a high-temperature furnace and heat it to 600°C. The mixture was kept at temperature C for 4 hours and then cooled to room temperature. The cooled silica powder and LiF-NaF-KF-CsF eutectic salt powder were weighed at a mass ratio of 3:7 and ball-milled in a ball mill jar for 2 hours. The homogeneous mixture was then placed in a crucible and heated to 480°C in a high-temperature furnace under a high-purity argon atmosphere of 99.99%. The mixture was kept at temperature C for 3 hours. After the holding time, the molten salt electrolyte material was poured into a cooling pan and cooled to room temperature. The cooled electrolyte material was then placed in a ball mill and ball-milled for 2 hours until it passed through an 80-mesh sieve to obtain SiO2@LiF-NaF-KF-CsF electrolyte powder. The morphology of the prepared SiO2@LiF-NaF-KF-CsF electrolyte powder was characterized by scanning electron microscopy, as shown below. Figure 1 As shown.

[0026] Example 2 Weigh 50g of porous silica material with a purity of 99% and place it in a crucible; place the crucible in a high-temperature furnace and heat it to 800°C. Hold at temperature C for 1 hour, then cool to room temperature. Weigh the cooled silica powder and LiF-NaF-KF eutectic salt powder at a mass ratio of 6:4, and ball mill them in a ball mill jar for 2 hours. Place the homogeneous mixture in a crucible. Place the crucible in a high-temperature furnace and heat to 480°C under a high-purity argon atmosphere of 99.99%. The material was heated to temperature C and held at that temperature for 3 hours. After the holding time, the molten salt electrolyte material was poured into a cooling pan and cooled to room temperature. The cooled electrolyte material was then placed in a ball mill and ball-milled for 2 hours until it passed through an 80-mesh sieve to obtain SiO2@LiF-NaF-KF electrolyte powder. The heat-treated porous silica material was subjected to nitrogen adsorption-desorption experiments, and the BET curves are shown below. Figure 2 As shown, this indicates that the material has a loose and porous structure.

[0027] Example 3 Weigh 50g of porous silica material with a purity of 99% and place it in a crucible; place the crucible in a high-temperature furnace and heat it to 300°C. The mixture was kept at temperature C for 6 hours and then cooled to room temperature. The cooled silica powder and NaF-KF-CsF eutectic salt powder were weighed at a mass ratio of 1:9 and ball-milled in a ball mill jar for 2 hours. The homogeneous mixture was then placed in a crucible and heated to 320°C in a high-temperature furnace under a high-purity nitrogen atmosphere of 99.99%. C and keep warm for 3 hours; after the heat preservation is completed, pour the molten salt electrolyte material into a cooling pan and cool it to room temperature; put the cooled electrolyte material into a ball mill jar and ball mill for 2 hours to make it pass through an 80-mesh sieve to obtain SiO2@NaF-KF-CsF electrolyte powder.

[0028] Application Example 1 Using SiO2@LiF-NaF-KF-CsF powder from Example 1 as the electrolyte membrane material, aluminum-silicon alloy powder as the negative electrode material, and NiF2 as the positive electrode material, electrode sheets of Ф54mm were pressed under 37 tons of pressure and assembled into a single cell by adding a heating unit. Fifteen single cells were connected in series to assemble a fluorine-ion thermal battery. After being kept at a constant temperature of +70℃ for 4 hours in a high-temperature oven, an open-load test was conducted. The open-load discharge curve is shown below. Figure 4 As shown.

[0029] Comparative Example 1 MgO@LiF-NaF-KF-CsF powder, with magnesium oxide as the adsorbent, was used as the electrolyte membrane material. Aluminum-silicon alloy powder was used as the negative electrode material, and NiF2 as the positive electrode material. Electrode sheets with a diameter of Ф54 mm were pressed under 37 tons of pressure and assembled into a single-cell battery by adding a heating unit. The ionic conductivity of the prepared MgO@LiF-NaF-KF-CsF monolayer electrode and the SiO2@LiF-NaF-KF-CsF monolayer electrode from Example 1 were compared by electrochemical impedance spectroscopy. Figure 3 As shown in the figure. Fifteen individual cells were connected in series to assemble a fluorine-ion thermal battery. After being kept at a constant temperature of +70℃ for 4 hours, an open-load test was conducted. The open-load discharge curve is shown in the figure. Figure 4 As shown.

[0030] The results of the no-load discharge curves of the fluorine-ion thermal batteries assembled in Application Example 1 and Comparative Example 1 show that when 24V is selected as the cutoff voltage, the high-temperature no-load time of the fluorine-ion thermal battery using porous silica as the molten salt adsorbent is extended by 32% compared with that of the fluorine-ion thermal battery using magnesium oxide as the adsorbent. This indicates that after reasonable alloying design of the molten salt adsorbent in the electrolyte of the fluorine-ion thermal battery, the good chemical stability and strong adsorption capacity of silica with the positive and negative electrode materials suppress the dissolution shuttle of the positive and negative electrode materials at high temperature, effectively extending the high-temperature no-load time.

[0031] The experimental results are shown in the table below.

[0032]

[0033] Experimental results show that, thanks to the good chemical stability and large specific surface area of ​​porous silica materials, the high-temperature no-load time of the fluoride ion thermal battery composed of silica-adsorbed molten salt electrolytes prepared in Examples 1-3 is extended by more than 20% compared with that of the magnesium oxide-adsorbed molten salt electrolyte in Comparative Example 1, and the electrolyte ionic conductivity is increased by more than 6.7%. This proves that the rationally designed molten salt electrolyte effectively improves the high-temperature no-load performance of the fluoride ion thermal battery.

[0034] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A molten salt electrolyte material, characterized in that, Based on mass percentage, it includes 10%-60% adsorbent carrier and 40%-90% molten eutectic salt.

2. The molten salt electrolyte material according to claim 1, characterized in that, The adsorption carrier is a porous silica material.

3. The molten salt electrolyte material according to claim 1, characterized in that, The molten eutectic salt is one of LiF-BeF2, NaF-BeF2, LiF-NaF-BeF2, LiF-ZrF4, NaF-ZrF4, KF-ZrF4, RbF-ZrF4, LiF-NaF-ZrF4, LiF-NaF-KF, NaF-KF-CsF, LiF-NaF-KF-CsF, and LiF-NaF-RbF.

4. The method for preparing the molten salt electrolyte material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Place the porous silica material in a high-temperature furnace, heat and keep it warm to remove high-temperature unstable impurities; (2) Weigh the cooled silica and eutectic salt according to the target stoichiometric ratio and mix them evenly; (3) Place the mixed materials in a high-temperature furnace, heat and keep warm under a special atmosphere; (4) After the heat preservation is completed, take out the molten salt electrolyte material and pour it into a cooling pan to cool to room temperature; (5) The cooled molten salt electrolyte is crushed and sieved to obtain molten salt electrolyte powder.

5. The method for preparing the molten salt electrolyte material according to claim 4, characterized in that, The porous silica material has an average pore size of 20-50 nm and a specific surface area of ​​100-200 m². 2 / g.

6. The method for preparing the molten salt electrolyte material according to claim 4, characterized in that, The purity of the silicon dioxide material is ≥99%; the purity of the eutectic salt raw materials is ≥99%.

7. The method for preparing the molten salt electrolyte material according to claim 4, characterized in that, The silicon dioxide is fired at a temperature of 300~800℃ and held for 1~6 hours.

8. The method for preparing the molten salt electrolyte material according to claim 4, characterized in that, The special atmosphere is either argon or nitrogen, with a purity of 99.99% or higher.

9. The method for preparing the molten salt electrolyte material according to claim 4, characterized in that, The molten salt electrolyte is heated at a temperature of 320~600℃ and held for 1~3 hours.

10. A fluorine-ion thermal battery, characterized in that, The electrolyte material is the molten salt electrolyte material according to any one of claims 1-3 or the molten salt electrolyte material prepared by any one of claims 4-9.

Images