A high-performance thermal battery electrolyte material and its preparation method

Abstract

This invention provides a high-performance thermal battery electrolyte material and its preparation method, belonging to the field of thermal battery technology. The high-performance thermal battery electrolyte material of this invention comprises the following raw materials in the following mass fractions: 25-40% inhibitor and 60-75% molten salt electrolyte; the inhibitor comprises hollow MgO powder, nano-γ-Al2O3, and magnesium fluoride; the mass ratio of hollow MgO powder, nano-γ-Al2O3, and magnesium fluoride is 2-4:1-3:1. This invention selects hollow MgO powder, nano-γ-Al2O3 powder, and magnesium fluoride powder together as inhibitors, and combines them with a quaternary or pentagonal molten salt electrolyte to significantly improve the conductivity and stability of the electrolyte material, lower the melting point of the electrolyte material, extend its service life, and broaden the operating temperature range of the thermal battery.

Description

Technical Field

[0001] This invention relates to the field of thermal battery technology, and in particular to a high-performance thermal battery electrolyte material and its preparation method. Background Technology

[0002] Thermal batteries are thermally activated, single-use reserve batteries, consisting of a positive electrode, electrolyte, negative electrode, heating system, activation system, and insulation system. Due to their characteristics such as low internal resistance, high specific energy and power, long storage time, low self-discharge, fast activation speed, and wide operating temperature range, thermal batteries are widely used in artillery, torpedoes, space exploration systems, and also extensively applied in emergency escape devices and underground high-temperature mining power supplies.

[0003] With the development of science and technology, there is a growing demand for longer operating lifespans of thermal batteries. Many fields now require thermal batteries to operate for tens of minutes or even several hours. Lowering the melting point of the thermal battery electrolyte allows it to remain in a molten state for a longer period, which is one way to extend battery life. Currently, the most commonly used electrolytes in thermal batteries are binary and ternary molten salt electrolytes. However, these electrolytes have drawbacks such as relatively high eutectic points and low conductivity, making it impossible to simultaneously meet the requirements of low melting point and high conductivity.

[0004] In thermal battery electrolytes, inhibitors such as MgO are typically added to prevent leakage and short circuits after the electrolyte melts upon heating. To increase the adsorption capacity of MgO powder on the electrolyte, the MgO powder content in the electrolyte must be increased. This inevitably leads to an increase in the internal resistance of the electrolyte, which is detrimental to the high-current output of the thermal battery. Furthermore, under prolonged operating conditions, the thermal battery electrolyte gradually thins, and its mechanical strength continuously decreases. The molten salt electrolyte can no longer be adsorbed into the MgO powder and will flow, severely affecting battery safety.

[0005] Therefore, it is of great significance to provide a thermal battery electrolyte material with low melting point, high conductivity, long working life and significantly improved stability prepared by a multi-element molten salt electrolyte and a composite inhibitor. Summary of the Invention

[0006] The purpose of this invention is to provide a high-performance thermal battery electrolyte material and its preparation method, addressing the shortcomings of existing technologies.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a high-performance thermal battery electrolyte material, which comprises the following raw materials by mass fraction: 25-40% inhibitor and 60-75% molten salt electrolyte; The inhibitor comprises hollow MgO powder, nano-γ-Al2O3 and magnesium fluoride; the mass ratio of hollow MgO powder, nano-γ-Al2O3 and magnesium fluoride is 2~4:1~3:1.

[0008] Preferably, the molten salt electrolyte is a quaternary molten salt electrolyte or a pentagonal molten salt electrolyte.

[0009] Preferably, the quaternary molten salt electrolyte comprises a mixture of lithium fluoride, lithium chloride, lithium bromide and cesium bromide, a mixture of lithium bromide, potassium bromide, cesium bromide and lithium iodide, or a mixture of lithium chloride, lithium bromide, potassium bromide and rubidium chloride. The pentaceous molten salt electrolyte comprises a mixture of lithium chloride, lithium bromide, potassium bromide, cesium bromide, and lithium iodide.

[0010] Preferably, the method for preparing the hollow MgO powder includes the following steps: 1) A precursor solution is obtained by mixing glucose solution and magnesium salt; the precursor solution is subjected to hydrothermal reaction and drying in sequence to obtain carbon spheres@MgO powder; 2) The carbon spheres@MgO powder is heat-treated to remove the nano-carbon spheres in the carbon spheres@MgO powder, resulting in hollow MgO powder.

[0011] Preferably, the glucose concentration in the glucose solution is 20-60 g / L, and the magnesium salt concentration in the precursor solution is 0.1-0.18 mol / L, wherein the magnesium salt is magnesium chloride or magnesium nitrate.

[0012] Preferably, the hydrothermal reaction temperature in step 1) is 150~180℃, the hydrothermal reaction time is 2~4h, the drying temperature is 80~95℃, and the drying time is 0.5~1.5h.

[0013] Preferably, the heat treatment temperature in step 2) is 500~700℃ and the heat treatment time is 0.5~1.5h.

[0014] Preferably, the hollow MgO powder has a particle size of 1~2.5μm and a specific surface area ≥360m². 2 / g; The magnesium fluoride and nano γ-Al2O3 are magnesium fluoride and nano γ-Al2O3 treated at high temperature, the temperature of which is 500~700℃ and the time is 1~3h.

[0015] The present invention also provides a method for preparing the high-performance thermal battery electrolyte material, comprising the following steps: ball milling an inhibitor and a molten salt electrolyte to obtain a mixture; melting and sintering the mixture; pulverizing and sieving the sintered product to obtain the high-performance thermal battery electrolyte material.

[0016] Preferably, the melting and sintering temperature is 500~600℃ and the melting and sintering time is 6~12h.

[0017] The beneficial effects of this invention are: 1) Magnesium fluoride has a good inhibitory effect on flowing electrolytes and excellent thermal stability. It is compatible with electrode materials and does not react. The combination of magnesium fluoride and magnesium oxide can improve the wetting and adsorption behavior of the interface between molten salt electrolyte and inhibitor, accelerate the ion conduction rate, improve ionic conductivity and the discharge capacity of thermal batteries, and meet the discharge requirements of thermal batteries. Hollow MgO powder can adsorb and fix more molten salt electrolytes, improve electrolyte retention at high temperatures, and make the electrolyte shape stable in the working range of thermal batteries, avoiding the problem of battery capacity reduction and battery failure caused by the reduction of structural strength of electrolyte in the later stage of discharge.

[0018] 2) The components of the quaternary molten salt electrolyte and the pentagonal molten salt electrolyte of the present invention work synergistically to regulate the ion conduction network, resulting in a lower melting point and higher conductivity. In the electrochemical system, they have the advantages of long discharge time and high discharge capacity, and reduce the lower operating temperature of the thermal battery.

[0019] 3) This invention selects hollow MgO powder, nano-γ-Al2O3 powder and magnesium fluoride powder as inhibitors, and combines them with quaternary molten salt electrolyte or pentagonal molten salt electrolyte to significantly improve the conductivity and stability of electrolyte materials, greatly reduce the melting point of electrolyte materials, extend working life, and broaden the working temperature range of thermal batteries. Detailed Implementation

[0020] This invention provides a high-performance thermal battery electrolyte material, which comprises the following raw materials by mass fraction: 25-40% inhibitor and 60-75% molten salt electrolyte; The inhibitor comprises hollow MgO powder, nano-γ-Al2O3 and magnesium fluoride; the mass ratio of hollow MgO powder, nano-γ-Al2O3 and magnesium fluoride is 2~4:1~3:1.

[0021] In the high-performance thermal battery electrolyte material of the present invention, the inhibitor is preferably 28-36%, more preferably 30-35%, and even more preferably 32-33%, and the molten salt electrolyte is preferably 64-72%, more preferably 65-70%, and even more preferably 67-68%.

[0022] In this invention, the molten salt electrolyte is preferably a quaternary molten salt electrolyte or a pentagonal molten salt electrolyte.

[0023] In this invention, the quaternary molten salt electrolyte preferably comprises a mixture of lithium fluoride, lithium chloride, lithium bromide and cesium bromide, a mixture of lithium bromide, potassium bromide, cesium bromide and lithium iodide, or a mixture of lithium chloride, lithium bromide, potassium bromide and rubidium chloride. The pentaceous molten salt electrolyte preferably comprises a mixture of lithium chloride, lithium bromide, potassium bromide, cesium bromide, and lithium iodide.

[0024] In this invention, the mass ratio of lithium fluoride, lithium chloride, lithium bromide, and cesium bromide in the mixture is preferably 8~15:20~25:50~55:10~20, more preferably 10~12:22~23:52~54:12~18, and even more preferably 11:23:53:15~16; the mass ratio of lithium bromide, potassium bromide, cesium bromide, and lithium iodide in the mixture is preferably 30~35:15~20:40~5 The mass ratio of lithium chloride, lithium bromide, potassium bromide and rubidium chloride in the mixture is preferably 35-40:30-36:25-30:5-12, more preferably 36-39:32-34:26-29:7-10, and even more preferably 37-38:33:27-28:8-9.

[0025] In this invention, the mass ratio of lithium chloride, lithium bromide, potassium bromide, cesium bromide, and lithium iodide in the mixture is preferably 10~15:25~30:15~20:25~30:10~20, more preferably 11~14:26~29:16~19:26~29:12~18, and even more preferably 12~13:27~28:17~18:27~28:15~16.

[0026] In this invention, the method for preparing the hollow MgO powder includes the following steps: 1) A precursor solution is obtained by mixing glucose solution and magnesium salt; the precursor solution is subjected to hydrothermal reaction and drying in sequence to obtain carbon spheres@MgO powder; 2) The carbon spheres@MgO powder is heat-treated to remove the nano-carbon spheres in the carbon spheres@MgO powder, resulting in hollow MgO powder.

[0027] In the glucose solution of the present invention, the concentration of glucose is preferably 20-60 g / L, more preferably 30-50 g / L, and even more preferably 40 g / L. In the precursor solution, the concentration of magnesium salt is preferably 0.1-0.18 mol / L, more preferably 0.12-0.16 mol / L, and even more preferably 0.14-0.15 mol / L. The magnesium salt is preferably magnesium chloride or magnesium nitrate.

[0028] In this invention, the temperature of the hydrothermal reaction in step 1) is preferably 150~180℃, more preferably 160~170℃, and even more preferably 165℃; the time of the hydrothermal reaction is preferably 2~4h, more preferably 2.5~3.5h, and even more preferably 3h; the temperature of the drying is preferably 80~95℃, more preferably 83~92℃, and even more preferably 85~90℃; the drying time is preferably 0.5~1.5h, and even more preferably 1h.

[0029] In this invention, the heat treatment temperature in step 2) is preferably 500~700℃, more preferably 550~650℃, and even more preferably 600℃, and the heat treatment time is preferably 0.5~1.5h, and even more preferably 1h.

[0030] In this invention, the hollow MgO powder preferably has a particle size of 1~2.5μm, more preferably 1.5~2μm, and a specific surface area preferably ≥360m². 2 / g, further optimized to ≥400m 2 / g; the magnesium fluoride and nano-γ-Al2O3 are preferably magnesium fluoride and nano-γ-Al2O3 after high-temperature treatment. The high-temperature treatment temperature is preferably 500~700℃, more preferably 550~650℃, and more preferably 600℃. The high-temperature treatment time is preferably 1~3h, more preferably 1.5~2.5h, and more preferably 2h.

[0031] In this invention, the specific surface area of ​​nano-γ-Al2O3 is preferably 180~230 m². 2 / g, with a preferred particle size of 20~70nm.

[0032] The present invention also provides a method for preparing the high-performance thermal battery electrolyte material, comprising the following steps: ball milling an inhibitor and a molten salt electrolyte to obtain a mixture; melting and sintering the mixture; pulverizing and sieving the sintered product to obtain the high-performance thermal battery electrolyte material.

[0033] In this invention, the melting and sintering temperature is preferably 500~600℃, more preferably 520~580℃, and even more preferably 550~560℃, and the melting and sintering time is preferably 6~12h, and even more preferably 8~10h.

[0034] The electrolyte material of this invention, when used in lithium-based thermal batteries, can significantly improve the discharge voltage and discharge capacity of lithium-based thermal batteries, thereby enhancing their electrical performance.

[0035] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0036] In the embodiments, the preparation process of the quaternary molten salt electrolyte or the pentagonal molten salt electrolyte is as follows: each component is sintered at 230°C and under an argon atmosphere for 6 hours and then pulverized into 100-mesh powder. The powder is then mixed according to the mass ratio of each component of the molten salt electrolyte. The mixture is sintered at 500°C under an argon atmosphere for 5 hours and then pulverized into 100-mesh powder to obtain the quaternary molten salt electrolyte or the pentagonal molten salt electrolyte.

[0037] Nano-γ-Al₂O₃ was treated at 600℃ for 2 h to obtain a specific surface area of ​​200 m². 2 / g, nano-γ-Al2O3 powder with a particle size of 50nm; magnesium fluoride was treated at 600℃ for 2h to obtain magnesium fluoride powder with a particle size of 50μm.

[0038] Example 1

[0039] A precursor solution was prepared by mixing 0.1 L of glucose aqueous solution (glucose concentration 40 g / L) with magnesium chloride, with a magnesium chloride concentration of 0.15 mol / L. The precursor solution was subjected to hydrothermal reaction at 165 °C for 3 h, followed by drying at 90 °C for 1 h to obtain carbon spheres@MgO powder. The carbon spheres@MgO powder was then heat-treated at 600 °C for 1 h to remove the nano-carbon spheres, resulting in a particle size of 1.5–2 μm and a specific surface area of ​​400 m². 2 / g hollow MgO powder.

[0040] Hollow MgO powder, nano-γ-Al2O3 powder, and magnesium fluoride powder were mixed evenly in a mass ratio of 3:2:1 to obtain the inhibitor; the quaternary molten salt electrolyte was a mixture of lithium fluoride, lithium chloride, lithium bromide, and cesium bromide, with a mass ratio of 11:23:53:15.

[0041] The inhibitor with a mass fraction of 35% and the quaternary molten salt electrolyte with a mass fraction of 65% were mixed and ball-milled. The diameter of the zirconia beads used for ball milling was 20 mm, the ball milling speed was 100 r / min, and the time was 1 h to obtain a mixture. The mixture was melt-sintered at 550℃ for 9 h, and the sintered product was crushed and passed through a 100-mesh sieve to obtain the thermal battery electrolyte material.

[0042] Example 2

[0043] A precursor solution was prepared by mixing 0.1 L of glucose aqueous solution (glucose concentration of 30 g / L) with magnesium nitrate, with a magnesium nitrate concentration of 0.12 mol / L. The precursor solution was subjected to hydrothermal reaction at 155 °C for 4 h, followed by drying at 85 °C for 1.5 h to obtain carbon spheres@MgO powder. The carbon spheres@MgO powder was then heat-treated at 650 °C for 0.5 h to remove the nano-carbon spheres, resulting in a particle size of 1–2.5 μm and a specific surface area of ​​390 m². 2 / g hollow MgO powder.

[0044] Hollow MgO powder, nano-γ-Al2O3 powder and magnesium fluoride powder were mixed evenly in a mass ratio of 2.5:1.5:1 to obtain the inhibitor; the quaternary molten salt electrolyte was a mixture of lithium chloride, lithium bromide, potassium bromide and rubidium chloride, with a mass ratio of lithium chloride, lithium bromide, potassium bromide and rubidium chloride of 37:33:27:8.

[0045] The inhibitor with a mass fraction of 28% and the quaternary molten salt electrolyte were mixed and ball-milled. The diameter of the zirconia beads used for ball milling was 20 mm, the ball milling speed was 100 r / min, and the time was 1 h to obtain a mixture. The mixture was melt-sintered at 500℃ for 10 h, and the sintered product was crushed and passed through a 100-mesh sieve to obtain the thermal battery electrolyte material.

[0046] Example 3

[0047] A precursor solution was prepared by mixing 0.1 L of glucose aqueous solution (50 g / L glucose concentration) with magnesium chloride to obtain a precursor solution with a magnesium chloride concentration of 0.16 mol / L. The precursor solution was subjected to hydrothermal reaction at 175 °C for 2 h, followed by drying at 95 °C for 0.5 h to obtain carbon spheres@MgO powder. The carbon spheres@MgO powder was then heat-treated at 550 °C for 1.5 h to remove the nano-carbon spheres, resulting in a particle size of 1–1.5 μm and a specific surface area of ​​420 m². 2 / g hollow MgO powder.

[0048] Hollow MgO powder, nano-γ-Al2O3 powder, and magnesium fluoride powder were mixed evenly in a mass ratio of 4:3:1 to obtain an inhibitor; the pentagonal molten salt electrolyte was a mixture of lithium chloride, lithium bromide, potassium bromide, cesium bromide, and lithium iodide, with a mass ratio of 12:27:17:28:16.

[0049] The inhibitor with a mass fraction of 36% and the pentagonal molten salt electrolyte were mixed and ball-milled. The diameter of the zirconia beads used for ball milling was 20 mm, the ball milling speed was 100 r / min, and the time was 1 h to obtain a mixture. The mixture was melt-sintered at 600℃ for 8 h, and the sintered product was crushed and passed through a 100-mesh sieve to obtain the thermal battery electrolyte material.

[0050] Comparative Example 1

[0051] The hollow MgO powder in Example 1 was replaced with ordinary MgO powder with a particle size of 1.5~2μm. Cesium bromide was omitted from the quaternary molten salt electrolyte. Lithium fluoride, lithium chloride and lithium bromide in a mass ratio of 11:23:53 were used to form a ternary molten salt electrolyte. Other process conditions were the same as in Example 1.

[0052] Comparative Example 2

[0053] The magnesium fluoride powder of Example 1 was omitted. Hollow MgO powder and nano γ-Al2O3 powder with a mass ratio of 1:2 were mixed evenly to obtain the inhibitor. The inhibitor with a mass fraction of 45% and the quaternary molten salt electrolyte with a mass fraction of 55% were used to prepare the electrolyte material for the thermal battery. Other process conditions were the same as in Example 1.

[0054] Comparative Example 3

[0055] The hollow MgO powder of Example 2 was omitted, and nano γ-Al2O3 powder and magnesium fluoride powder were mixed evenly in a mass ratio of 4:1 to obtain the inhibitor; rubidium chloride in the quaternary molten salt electrolyte was omitted, and lithium chloride, lithium bromide and potassium bromide in a mass ratio of 37:33:27 were used to form the ternary molten salt electrolyte; other process conditions were the same as in Example 2.

[0056] The conductivity, melting point and stability of the thermal battery electrolyte materials of Examples 1-3 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0057] Conductivity testing method: The conductivity of the electrolyte material is determined by the continuously changing cell constant method (CVCC method). At 500℃, the resistance of the molten salt between the two electrodes is measured by electrochemical impedance spectroscopy at different displacements of the working electrode, and the conductivity at 500℃ is obtained by the CVCC method.

[0058] Melting point test method: The melting point of the electrolyte material was tested using a Hitachi STA200RV simultaneous thermogravimetric analyzer, using an Al2O3 crucible, with argon gas as the analytical atmosphere, and a heating rate of 10℃ / min.

[0059] Electrolyte stability test: The electrolyte material was pressed into an electrolyte sheet with a thickness of 0.5 mm under 20 MPa, and then heat-treated at 500℃ for 2 h to test the electrolyte retention rate.

[0060] Table 1 Performance test results of different electrolyte materials

[0061] As can be seen from the examples and comparative examples, the present invention obtains an inhibitor by combining hollow MgO powder, nano γ-Al2O3 powder and magnesium fluoride powder, and combines it with a specific quaternary molten salt electrolyte or pentagonal molten salt electrolyte to control the proportion of each raw material, which significantly improves the conductivity and retention rate of the electrolyte material and lowers the melting point, thus significantly improving the electrical performance of the thermal battery and widening its operating temperature range.

[0062] 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 principle 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 high-performance thermal battery electrolyte material, characterized in that, The high-performance thermal battery electrolyte material comprises the following raw materials by mass fraction: 25-40% inhibitor and 60-75% molten salt electrolyte; The inhibitor comprises hollow MgO powder, nano-γ-Al2O3 and magnesium fluoride; the mass ratio of hollow MgO powder, nano-γ-Al2O3 and magnesium fluoride is 2~4:1~3:

1.

2. The high-performance thermal battery electrolyte material according to claim 1, characterized in that, The molten salt electrolyte is a quaternary molten salt electrolyte or a pentagonal molten salt electrolyte.

3. The high-performance thermal battery electrolyte material according to claim 1 or 2, characterized in that, The quaternary molten salt electrolyte comprises a mixture of lithium fluoride, lithium chloride, lithium bromide and cesium bromide, a mixture of lithium bromide, potassium bromide, cesium bromide and lithium iodide, or a mixture of lithium chloride, lithium bromide, potassium bromide and rubidium chloride. The pentaceous molten salt electrolyte comprises a mixture of lithium chloride, lithium bromide, potassium bromide, cesium bromide, and lithium iodide.

4. The high-performance thermal battery electrolyte material according to claim 3, characterized in that, The method for preparing the hollow MgO powder includes the following steps: 1) A precursor solution is obtained by mixing glucose solution and magnesium salt; the precursor solution is subjected to hydrothermal reaction and drying in sequence to obtain carbon spheres@MgO powder; 2) The carbon spheres@MgO powder is heat-treated to remove the nano-carbon spheres in the carbon spheres@MgO powder, resulting in hollow MgO powder.

5. The high-performance thermal battery electrolyte material according to claim 4, characterized in that, In the glucose solution, the concentration of glucose is 20~60 g / L, and in the precursor solution, the concentration of magnesium salt is 0.1~0.18 mol / L, and the magnesium salt is magnesium chloride or magnesium nitrate.

6. The high-performance thermal battery electrolyte material according to claim 4 or 5, characterized in that, Step 1) The hydrothermal reaction temperature is 150~180℃, the hydrothermal reaction time is 2~4h, the drying temperature is 80~95℃, and the drying time is 0.5~1.5h.

7. The high-performance thermal battery electrolyte material according to claim 6, characterized in that, Step 2) The heat treatment temperature is 500~700℃ and the heat treatment time is 0.5~1.5h.

8. The high-performance thermal battery electrolyte material according to claim 7, characterized in that, The hollow MgO powder has a particle size of 1~2.5μm and a specific surface area ≥360m². 2 / g; The magnesium fluoride and nano γ-Al2O3 are magnesium fluoride and nano γ-Al2O3 treated at high temperature, the temperature of which is 500~700℃ and the time is 1~3h.

9. A method for preparing the high-performance thermal battery electrolyte material according to any one of claims 1 to 8, characterized in that, The process includes the following steps: ball milling the inhibitor and molten salt electrolyte to obtain a mixture; melting and sintering the mixture; pulverizing and sieving the sintered product to obtain a high-performance thermal battery electrolyte material.

10. The preparation method according to claim 9, characterized in that, The melting and sintering temperature is 500~600℃, and the melting and sintering time is 6~12h.

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