Molten salt electrolyte and application thereof

Abstract

The invention discloses a molten salt electrolyte. The molten salt electrolyte provided by the invention is prepared from the following components: 3.0 mol% to 6.0 mol% of LiF, 5.0 mol% to 15.0 mol% of LiCl, 60.0 mol% to 75.0 mol% of LiBr and 18.0 mol% to 25.0 mol% of CsCl. The invention also discloses application of the molten salt electrolyte in the fields of thermal batteries and molten salt heat transfer and energy storage. According to the invention, the LiF-LiCl-LiBr-CsCl molten salt electrolyte with the melting point of 269.0 + / -2.0 DEG C, the conductivity of not less than 1.89 S / cm at the temperature of 500.0 DEG C and the decomposition temperature of 804.0 DEG C is provided and prepared for the first time. Compared with a common LiCl-LiBr-KBr electrolyte, the molten salt electrolyte has the advantages that the melting point is reduced by 52.0 DEG C, the conductivity at 500.0 DEG C is improved by at least 0.16 S / cm, the energy consumption is reduced by 93.9 J / g, the decomposition temperature is improved by 40.0 DEG C, and the electrochemical window is widened by at least 20.0 mV (400.0-500.0 DEG C), so that the service life of a thermal battery can be effectively prolonged, the activation time of the thermal battery can be effectively shortened, the working temperature range of the thermal battery can be widened, and the service life of the thermal battery can be prolonged. The fused salt electrolyte is a very potential candidate fused salt electrolyte, and has a huge application value in the fields of thermal batteries and fused salt heat transfer and energy storage.

Description

Technical Field

[0001] This invention relates to a molten salt electrolyte, belonging to the field of thermal battery and molten salt heat transfer and energy storage technology. Background Technology

[0002] Thermal batteries are primary irreversible chemical power sources that use molten salt as the electrolyte. Due to their advantages such as high specific energy, high output power, long storage time, compact structure, and resistance to harsh conditions, they are widely used as power sources in aerospace, electronic warfare, artillery shells, and missiles. Thermal batteries have become ideal power sources for modern weapons, playing an indispensable role in the military industry. With the rapid development of advanced weaponry, the performance requirements for thermal batteries, as key energy components, such as long lifespan and high reliability, are becoming increasingly prominent. Lowering the melting point of the molten salt electrolyte used in thermal batteries and improving its conductivity and thermal stability not only allows the thermal battery to remain in a molten state for extended periods but also reduces the internal and external temperature difference and widens its operating temperature range, which is a crucial measure to improve thermal battery performance. Therefore, it is essential to develop new electrolytes for thermal batteries with low melting points and high conductivity to meet the electrolyte material requirements of power sources for advanced weapons.

[0003] Currently, commonly used electrolytes for thermal batteries include LiF-LiCl-LiBr, LiCl-KCl, and LiCl-LiBr-KBr. Among them, LiF-LiCl-LiBr exhibits high conductivity (3.39 S / cm @ 500.0). o C) is a commonly used electrolyte in thermal batteries, but this salt has a melting point of 443.0°C. o C) Problems such as high efficiency and low anode utilization limit its development potential. LiCl-KCl has a relatively low melting point of 353.0°C. o C, High electrical conductivity (1.85 S / cm @ 500.0) o C) It is also commonly used as an electrolyte in thermal batteries, but during long-term use, polarization easily occurs at the interface between the positive electrode and the electrolyte, causing the electrolyte to solidify prematurely and leading to premature battery failure. LiCl-LiBr-KBr has a low melting point of 321.0°C. o C, but its conductivity is relatively low, at 1.73 S / cm @ 500.0 o C, which limits their high-current discharge capability, allowing them to only meet discharge requirements under normal current conditions. Although they are commonly used electrolytes in thermal batteries, they still suffer from problems such as high melting point, low conductivity, or insufficient specific energy. In particular, it is difficult to balance low melting point and high conductivity, making it impossible to meet the requirements of modern weapons for thermal battery electrolyte materials.

[0004] To improve the overall performance of existing molten salt electrolytes, researchers have conducted extensive studies. Zhong Jin et al. (CN102569836A) developed a LiBr-KBr-CsBr-LiI molten salt electrolyte (20.0~25.0 wt%, 12.0~18.0 wt%, 25.0~30.0 wt%, 27.0~43.0 wt%) with a melting point of 236.4 ℃, but its conductivity was only 0.142 S / cm (500.0 ℃). Wu Qibing et al. (CN102437345A) developed a LiBr-KBr-CsBr-LiI molten salt electrolyte (25.0~35.0 wt%, 10.0~22.0 wt%, 45.0~53.0 wt%, 8.0~13.0 wt%) with a melting point below 200.0 ℃ and a conductivity greater than 1.8 S / cm (500.0 ℃). Although both electrolytes have melting points below 236.5 ℃, they both contain air-sensitive iodides, which are easily oxidized to elemental iodine. This places high demands on the preparation environment of the thermal battery, restricting its large-scale production and application. Yang Xiaowei et al. (CN111490261A) developed a LiCl-LiBr-KBr-RbCl (34.0~40.0 wt%, 30.0~40.0 wt%, 20.0~30.0 wt%, 5.0~15.0 wt%) molten salt electrolyte, but its melting point is relatively high, at 293.0-303.0 ℃; at the same time, RbCl is expensive and has a high lattice energy, which will increase the energy consumption of the thermal battery, thus limiting its practical application.

[0005] In summary, while significant research has been conducted on electrolytes with superior overall performance, current technologies remain incomplete. Existing electrolytes often suffer from high melting points, low conductivity, or high energy consumption, failing to meet the demands of thermal batteries for electrolytes with low melting points, high conductivity, and high stability. Therefore, research and development of electrolytes with low melting points and high conductivity, without compromising their suitability for large-scale production and application, should be accelerated. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a molten salt electrolyte that has the characteristics of low melting point, high conductivity and low energy consumption, and has excellent comprehensive performance, which can better meet the needs of fields such as thermal batteries and molten salt heat transfer and energy storage.

[0007] The present invention specifically adopts the following technical solutions to solve the above-mentioned technical problems: A molten salt electrolyte having the following composition: 3.0–6.0 mol% LiF, 5.0–15.0 mol% LiCl, 60.0–75.0 mol% LiBr, and 18.0–25.0 mol% CsCl.

[0008] In the first embodiment, the composition is: 5.0 mol% LiF, 12.0 mol% LiCl, 63.0 mol% LiBr, and 20.0 mol% CsCl.

[0009] In the second embodiment, the composition is: 4.0 mol% LiF, 9.6 mol% LiCl, 64.4 mol% LiBr, and 22.0 mol% CsCl.

[0010] In the third embodiment, the composition is: 3.4 mol% LiF, 7.2 mol% LiCl, 65.4 mol% LiBr, and 24.0 mol% CsCl.

[0011] In the fourth embodiment, the composition is: 3.4 mol% LiF, 6.5 mol% LiCl, 70.8 mol% LiBr, and 19.3 mol% CsCl.

[0012] Preferably, the molten salt electrolyte is prepared by the following method: after mixing the components evenly in proportion, heating to 450.0-650.0 ℃ at a heating rate of 2.0-9.0 ℃ / min under an inert atmosphere and holding at that temperature for 0.5-9.0 h, and then cooling to room temperature.

[0013] More preferably, a glass carbon rod is used to stir the mixture during the heat preservation process to ensure uniform mixing.

[0014] Applications of molten salt electrolytes in thermal batteries and molten salt heat transfer energy storage as described in any of the above technical solutions.

[0015] Compared with the prior art, the technical solution of the present invention has the following beneficial effects: This invention, based on LiF-LiCl-LiBr, creatively adds CsCl and, through regulation and optimization of the molten salt composition, yields a LiF-LiCl-LiBr-CsCl molten salt electrolyte with a melting point of 269.0±2.0 ℃, a conductivity of no less than 1.89 S / cm at 500.0 ℃, and a decomposition temperature as high as 804.0 ℃. Compared with existing LiCl-LiBr-KBr molten salt electrolytes, this invention's molten salt electrolyte exhibits a 52.0 ℃ lower melting point, an at least 0.16 S / cm increase in conductivity at 500.0 ℃, a 93.9 J / g lower energy consumption, a 40.0 ℃ higher decomposition temperature, and a widened electrochemical window of at least 20.0 mV (400.0-500.0 ℃). This effectively extends the working life of thermal batteries, shortens their activation time, and broadens their operating temperature range, making it a highly promising candidate molten salt electrolyte with significant application value in thermal batteries and molten salt heat transfer energy storage. Attached Figure Description

[0016] Figure 1 This is the DSC curve of Example 1; Figure 2 This is the DSC curve of Example 2; Figure 3 This is the DSC curve of Example 3; Figure 4 This is the DSC curve of Example 4; Figure 5 This is the DSC curve for comparison 1; Figure 6 This is the DSC curve for Comparative Example 2; Figure 7 This is the DSC curve for Comparative Example 3; Figure 8 This is the DSC curve for Comparative Example 4.

[0017] Figure 9 This is a comparison chart of electrochemical window data for Example 4 and Comparative Example 4; Figure 10 This is a comparison of the impedance spectra of Example 4 and Comparative Example 4; Figure 11 This is a comparison chart of energy consumption data between Example 4 and Comparative Example 4; Figure 12 This is a comparison chart of the thermal stability test results of Example 4 and Comparative Example 4. Detailed Implementation

[0018] To address the shortcomings of existing technologies in meeting the electrolyte requirements of thermal batteries, this invention creatively adds CsCl to the widely used ternary molten salt LiF-LiCl-LiBr. By regulating and optimizing the molten salt composition, a molten salt electrolyte with superior overall performance, characterized by low melting point, high conductivity, and low energy consumption, is obtained, thereby better meeting the needs of thermal batteries, molten salt heat transfer and energy storage, and other fields.

[0019] The molten salt electrolyte proposed in this invention has the following composition: 3.0–6.0 mol% LiF, 5.0–15.0 mol% LiCl, 60.0–75.0 mol% LiBr, and 18.0–25.0 mol% CsCl.

[0020] Preferably, the molten salt electrolyte is prepared by the following method: after mixing the components evenly in proportion, heating to 450.0-650.0 ℃ at a heating rate of 2.0-9.0 ℃ / min under an inert atmosphere and holding at that temperature for 0.5-9.0 h, and then cooling to room temperature.

[0021] More preferably, a glass carbon rod is used to stir the mixture during the heat preservation process to ensure uniform mixing.

[0022] To facilitate public understanding, the technical solution and its effects of the present invention will be described in detail below through specific embodiments and comparative examples, in conjunction with the accompanying drawings: Anhydrous LiF (analytical grade, 99.5%), LiCl (analytical grade, 99.5%), LiBr (analytical grade, 99.5%), and CsCl (analytical grade, 99.0%) molten salts were placed in a glove box containing a high-purity inert atmosphere beforehand. Then, these molten salts were placed separately into glassy carbon crucibles and transferred to a high-temperature resistance furnace within the glove box. The furnace was heated to 180.0 °C at a heating rate of 5.0 °C / min and held at that temperature for 8.0 h to remove moisture from the molten salts. The remaining molten salts were then stored in the glove box for later use.

[0023] Example 1 In this embodiment, the composition of the molten salt electrolyte is: 5.0 mol% LiF, 12.0 mol% LiCl, 63.0 mol% LiBr, and 20.0 mol% CsCl.

[0024] The pretreated 1.4 g of LiF, 5.4 g of LiCl, 57.7 g of LiBr, and 35.5 g of CsCl were weighed separately using an electronic balance (accuracy 0.1 mg). After thorough mixing, the mixture was placed in a glassy carbon crucible and then transferred to a high-temperature resistance furnace. The furnace was heated to 550.0 °C at a heating rate of 5.0 °C / min and held at that temperature for 6.0 h. During the holding period, the mixture was stirred with a glassy carbon rod to ensure uniform mixing. Finally, the liquid molten salt was poured out and cooled to room temperature to obtain the LiF-LiCl-LiBr-CsCl molten salt electrolyte of this embodiment. All these experimental operations were carried out in a glove box containing a high-purity inert atmosphere.

[0025] The prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using a differential scanning calorimeter. The test results are as follows: Figure 1 As shown, the melting point of this embodiment is 271.0 °C, and the enthalpy of fusion is 46.7 J / g. The conductivity of the prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using the continuously varying cell constant method, and the conductivity of the molten salt electrolyte in this embodiment at 500.0 °C was found to be 1.95 S / cm.

[0026] Example 2 In this embodiment, the composition of the molten salt electrolyte is: 4.0 mol% LiF, 9.6 mol% LiCl, 64.4 mol% LiBr, and 22.0 mol% CsCl.

[0027] The pretreated 1.1 g of LiF, 4.1 g of LiCl, 57.1 g of LiBr, and 37.7 g of CsCl were weighed separately using an electronic balance (accuracy 0.1 mg). After thorough mixing, the mixture was placed in a glassy carbon crucible and then transferred to a high-temperature resistance furnace. The furnace was heated to 550.0 °C at a heating rate of 5.0 °C / min and held at that temperature for 6.0 h. During the holding process, the mixture was stirred with a glassy carbon rod to ensure uniform mixing. Finally, the liquid molten salt was poured out and cooled to room temperature to obtain the LiF-LiCl-LiBr-CsCl molten salt electrolyte of this embodiment. All these experimental operations were carried out in a glove box containing a high-purity inert atmosphere.

[0028] The prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using a differential scanning calorimeter. The test results are as follows: Figure 2As shown, the melting point of this embodiment is 269.0 °C, and the enthalpy of fusion is 55.2 J / g. The conductivity of the prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using the continuously varying cell constant method, and the conductivity of the molten salt electrolyte in this embodiment at 500.0 °C was found to be 1.92 S / cm.

[0029] Example 3 In this embodiment, the composition of the molten salt electrolyte is: 3.4 mol% LiF, 7.2 mol% LiCl, 65.4 mol% LiBr, and 24.0 mol% CsCl.

[0030] The pre-treated 0.9 g of LiF, 3.0 g of LiCl, 56.2 g of LiBr, and 39.9 g of CsCl were weighed separately using an electronic balance (accuracy 0.1 mg). After thorough mixing, the mixture was placed in a glassy carbon crucible and then transferred to a high-temperature resistance furnace. The furnace was heated to 550.0 °C at a heating rate of 5.0 °C / min and held at this temperature for 6.0 h. During the holding process, the mixture was stirred with a glassy carbon rod to ensure uniform mixing. Finally, the liquid molten salt was poured out and cooled to room temperature to obtain the LiF-LiCl-LiBr-CsCl molten salt electrolyte of this embodiment. All these experimental operations were carried out in a glove box containing a high-purity inert atmosphere.

[0031] The prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using a differential scanning calorimeter. The test results are as follows: Figure 3 As shown, the melting point of this embodiment is 269.0 °C, and the enthalpy of fusion is 54.2 J / g. The conductivity of the prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using the continuously varying cell constant method, and the conductivity of the molten salt electrolyte in this embodiment at 500.0 °C was found to be 1.89 S / cm.

[0032] Example 4 In this embodiment, the composition of the molten salt electrolyte is: 3.4 mol% LiF, 6.5 mol% LiCl, 70.8 mol% LiBr, and 19.3 mol% CsCl.

[0033] The pre-treated 0.9 g of LiF, 2.8 g of LiCl, 62.9 g of LiBr, and 33.4 g of CsCl were weighed separately using an electronic balance (accuracy 0.1 mg). After thorough mixing, the mixture was placed in a glassy carbon crucible and then transferred to a high-temperature resistance furnace. The furnace was heated to 550.0 °C at a heating rate of 5.0 °C / min and held at that temperature for 6.0 h. During the holding period, the mixture was stirred with a glassy carbon rod to ensure uniform mixing. Finally, the liquid molten salt was poured out and cooled to room temperature to obtain the LiF-LiCl-LiBr-CsCl molten salt electrolyte of this embodiment. All these experimental operations were carried out in a glove box containing a high-purity inert atmosphere.

[0034] The prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using a differential scanning calorimeter. The test results are as follows: Figure 4 As shown, the melting point of this embodiment is 267.0 °C and the enthalpy of fusion is 46.7 J / g. The conductivity of the prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using the continuously varying cell constant method, and the conductivity of the molten salt electrolyte in this embodiment at 500.0 °C was found to be 1.98 S / cm.

[0035] The electrochemical performance of the molten salt electrolyte in this embodiment was measured using a three-electrode system. Cyclic voltammetry (CV) was used to measure the electrochemical window of the molten salt electrolyte in the range of 400.0-500.0 °C. The scan rate was 0.1 V / s, and the scan potential range was -2.5 V to 1.8 V. Three repeated scans were performed, and the test results are as follows. Figure 9 As shown, the electrochemical window obtained in this embodiment is 3.28 V at 400.0 °C, 3.21 V at 425.0 °C, 3.13 V at 450.0 °C, 3.04 V at 470.0 °C, and 2.91 V at 500.0 °C. Electrochemical impedance spectroscopy (EIS) was used to measure the impedance spectrum of the molten salt electrolyte in this embodiment at 500.0 °C, and the test results are as follows. Figure 10 As shown, the resistance of the molten salt electrolyte in this embodiment is 1.039 Ω.

[0036] The average solid and liquid specific heat capacities of the molten salt electrolyte in this embodiment were measured using differential scanning calorimetry and were found to be 0.37 J / (g·°C) and 0.73 J / (g·°C), respectively. The energy consumed by the molten salt electrolyte in this embodiment to heat from room temperature to 600.0 °C was calculated using formula (1). The results are as follows... Figure 11 As shown, the energy consumed by the molten salt electrolyte in this embodiment is 425.4 J / g.

[0037] (1) in H sum (J / g) represents the total heat required for molten salt electrolyte. T m It's the melting point. T a ( T a =25 ℃) is the initial heating temperature. C p (sol.) represents the specific heat capacity of the solid state. ΔH fusion (J / g) is the enthalpy of fusion. T b Operating temperature C p (liq.) represents the specific heat capacity of liquid.

[0038] The decomposition temperature of the molten salt electrolyte in this embodiment was tested using a simultaneous thermal analyzer (STA), and the results are as follows: Figure 12 As shown, the decomposition temperature of the molten salt electrolyte in this embodiment is 804.0 °C.

[0039] To verify the rationality and accuracy of the molten salt electrolyte composition proposed in this invention, the following comparative experiments were further conducted: Comparative Example 1 The pretreated 1.8 g of LiF, 24.2 g of LiCl, 62.0 g of LiBr, and 12.0 g of CsCl were weighed separately using an electronic balance (accuracy 0.1 mg). After thorough mixing, the mixture was placed in a glassy carbon crucible and then transferred to a high-temperature resistance furnace. The furnace was heated to 550.0 °C at a heating rate of 5.0 °C / min and held at this temperature for 6.0 h. During the holding period, the mixture was stirred with a glassy carbon rod to ensure uniform mixing. Finally, the liquid molten salt was poured out and cooled to room temperature to obtain the LiF-LiCl-LiBr-CsCl molten salt electrolyte of this comparative example. All these experimental operations were performed in a glove box containing a high-purity inert atmosphere.

[0040] The prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using a differential scanning calorimeter. The test results are as follows: Figure 5 As shown, the melting peak is not a regular single peak and exhibits segmentation, indicating that the molten salt in this comparative example is not a eutectic system. However, the initial melting temperature of this comparative example is as high as 376.0 ℃, and the enthalpy of melting is 84.9 J / g. The conductivity of the prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using the continuously varying cell constant method. The conductivity of the molten salt electrolyte in this comparative example at 500.0 ℃ was found to be 2.21 S / cm.

[0041] Comparative Example 2 The pretreated 1.7 g LiF, 19.4 g LiCl, 56.9 g LiBr, and 22.0 g CsCl were weighed separately using an electronic balance (accuracy 0.1 mg). After thorough mixing, the mixture was placed in a glassy carbon crucible and then transferred to a high-temperature resistance furnace. The furnace was heated to 550.0 °C at a heating rate of 5.0 °C / min and held at this temperature for 6.0 h. During the holding period, the mixture was stirred with a glassy carbon rod to ensure uniform mixing. Finally, the liquid molten salt was poured out and cooled to room temperature to obtain the LiF-LiCl-LiBr-CsCl molten salt electrolyte of this comparative example. All these experimental operations were performed in a glove box containing a high-purity inert atmosphere.

[0042] The prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using a differential scanning calorimeter. The test results are as follows: Figure 6 As shown, the melting peak is not a regular single peak and exhibits segmentation, indicating that the molten salt in this comparative example is not a eutectic system. However, the initial melting temperature of this comparative example is as high as 362.0 ℃, and the enthalpy of melting is 40.7 J / g. The conductivity of the prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using the continuously varying cell constant method. The conductivity of the molten salt electrolyte in this comparative example at 500.0 ℃ was found to be 2.11 S / cm.

[0043] Comparative Example 3 2.0 g of pretreated LiF, 8.7 g of LiCl, 60.3 g of LiBr, and 29.0 g of CsCl were weighed separately using an electronic balance (accuracy 0.1 mg). After thorough mixing, the mixture was placed in a glassy carbon crucible and then transferred to a high-temperature resistance furnace. The furnace was heated to 550.0 °C at a heating rate of 5.0 °C / min and held at this temperature for 6.0 h. During the holding period, the mixture was stirred with a glassy carbon rod to ensure uniform mixing. Finally, the liquid molten salt was poured out and cooled to room temperature to obtain the LiF-LiCl-LiBr-CsCl molten salt electrolyte of this comparative example. All these experimental operations were performed in a glove box containing a high-purity inert atmosphere.

[0044] The prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using a differential scanning calorimeter. The test results are as follows: Figure 7As shown, the melting peak is not a regular single peak and exhibits segmentation, indicating that the molten salt in this comparative example is not a eutectic system. However, the initial melting temperature of this comparative example is as high as 336.0 ℃, and the enthalpy of melting is 63.1 J / g. The conductivity of the prepared LiF-LiCl-LiBr-CsCl molten salt electrolyte was tested using the continuously varying cell constant method. The conductivity of the molten salt electrolyte in this comparative example at 500.0 ℃ was found to be 2.04 S / cm.

[0045] Comparative Example 4 The molten salt electrolyte used in this comparative example is the commonly used ternary LiF-LiCl-LiBr molten salt. Using an electronic balance (accuracy 0.1 mg), 12.0 g of pre-treated LiF, 36.5 g of LiCl, and 51.5 g of LiBr were weighed separately. After thorough mixing, the mixture was placed in a glassy carbon crucible and then transferred to a high-temperature resistance furnace. The furnace was heated to 550.0 °C at a heating rate of 5.0 °C / min and held at this temperature for 6.0 h. During the holding period, the mixture was stirred with a glassy carbon rod to ensure uniform mixing. Finally, the liquid molten salt was poured out and cooled to room temperature to obtain the LiF-LiCl-LiBr molten salt electrolyte of this comparative example. All these experimental operations were performed in a glove box containing a high-purity inert atmosphere.

[0046] The LiF-LiCl-LiBr molten salt electrolyte prepared above was tested using a differential scanning calorimeter. The test results are as follows: Figure 8 As shown, the melting point of this comparative example is as high as 321.0 ℃, and the enthalpy of fusion is 96.3 J / g. The conductivity of the prepared LiF-LiCl-LiBr molten salt electrolyte was tested using the continuously varying cell constant method, and the conductivity of the molten salt electrolyte of this comparative example at 500.0 ℃ was found to be 1.73 S / cm.

[0047] The electrochemical performance of this comparative molten salt electrolyte was measured using a three-electrode system. Cyclic voltammetry (CV) was used to measure the electrochemical window of the comparative molten salt electrolyte in the range of 400.0–500.0 °C. The scan rate was 0.1 V / s, and the scan potential range was -2.5 V to 1.8 V. Three repeated scans were performed, and the test results are as follows: Figure 9 As shown, the electrochemical window of this comparative example was 3.24 V at 400.0 °C, 3.18 V at 425.0 °C, 3.11 V at 450.0 °C, 2.99 V at 470.0 °C, and 2.80 V at 500.0 °C. Electrochemical impedance spectroscopy (EIS) was used to measure the impedance spectrum of the molten salt electrolyte of this comparative example at 500.0 °C, and the test results are shown below. Figure 10As shown, the resistance of this comparative example is 1.107 Ω.

[0048] The average solid and liquid specific heat capacities of the comparative molten salt electrolyte were measured using differential scanning calorimetry and were found to be 0.57 J / (g·°C) and 0.74 J / (g·°C), respectively. The energy consumed by the comparative molten salt electrolyte to heat from room temperature to 600.0 °C was calculated using formula (1). The results are as follows: Figure 11 As shown, the energy consumed by the molten salt electrolyte in this comparative example is 519.3 J / g. The decomposition temperature of the molten salt electrolyte in this comparative example was measured using a simultaneous thermal analyzer (STA), and the results are as follows. Figure 12 As shown, the decomposition temperature of the molten salt electrolyte in this comparative example is 764.0 °C.

[0049] The melting point and conductivity data of Examples 1-4, Comparative Examples 1-4, and LiCl-KCl (58.8-41.2 mol%) are shown in Table 1.

[0050] Table 1

[0051] In summary, the LiF-LiCl-LiBr-CsCl molten salt electrolyte proposed in this invention has a melting point of 269.0±2.0℃, a conductivity of no less than 1.89 S / cm at 500.0℃, and a decomposition temperature as high as 804.0℃. Its melting point is 84.0℃ lower than that of the classic molten salt electrolyte LiCl-KCl, while its conductivity is increased by at least 0.04 S / cm. Compared with the common LiCl-LiBr-KBr molten salt electrolyte, its melting point is reduced by 52.0℃, its conductivity at 500.0℃ is increased by at least 0.16 S / cm, its energy consumption is reduced by 93.9 J / g, its decomposition temperature is increased by 40.0℃, and its electrochemical window is broadened by at least 20.0 mV (400.0-500.0℃). This can effectively extend the working life of thermal batteries, shorten the activation time, and broaden the operating temperature range, making it a very promising candidate molten salt electrolyte. However, when the ratio of LiF, LiCl, LiBr, and CsCl is not within the range defined by this invention (see Comparative Examples 1-3), the melting temperature increases significantly. This not only increases the temperature difference between the inside and outside of the thermal battery, leading to an increase in the cost of the thermal insulation material required for the thermal battery, but also shortens the working life of the thermal battery.

Claims

1. A molten salt electrolyte, characterized in that, Its composition is: 3.0–6.0 mol% LiF, 5.0–15.0 mol% LiCl, 60.0–75.0 mol% LiBr, and 18.0–25.0 mol% CsCl.

2. The molten salt electrolyte as described in claim 1, characterized in that, Its composition is: 5.0 mol% LiF, 12.0 mol% LiCl, 63.0 mol% LiBr, and 20.0 mol% CsCl.

3. The molten salt electrolyte as described in claim 1, characterized in that, Its composition is: 4.0 mol% LiF, 9.6 mol% LiCl, 64.4 mol% LiBr, and 22.0 mol% CsCl.

4. The molten salt electrolyte as described in claim 1, characterized in that, Its composition is: 3.4 mol% LiF, 7.2 mol% LiCl, 65.4 mol% LiBr, and 24.0 mol% CsCl.

5. The molten salt electrolyte as described in claim 1, characterized in that, Its composition is: 3.4 mol% LiF, 6.5 mol% LiCl, 70.8 mol% LiBr, and 19.3 mol% CsCl.

6. The molten salt electrolyte according to any one of claims 1-5, characterized in that, The sample was prepared by the following method: after mixing the components evenly in proportion, it was heated to 450.0-650.0 ℃ at a heating rate of 2.0-9.0 ℃ / min under an inert atmosphere and held at that temperature for 0.5-9.0 h, and then cooled to room temperature.

7. The molten salt electrolyte as described in claim 6, characterized in that, During the heat preservation process, use a glass carbon rod to stir the mixture to ensure it is evenly mixed.

8. The application of the molten salt electrolyte as described in any one of claims 1-7 in the fields of thermal batteries and molten salt heat transfer energy storage.

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